This year's CCA of the Year winner was Allan James, technical services agronomist at Mid Valley Agricultural Services and CCA of eight years.
The 2023 Crop Consultant Conference, hosted on September 27 and 28 in a collaborative effort by JCS Marketing Inc. and Western Region Certified Crop Advisers (WRCCA), saw another year of record attendance and provided the opportunity for crop consultants, industry suppliers, researchers and others to network and learn.
In addition to CCAs, PCAs and growers receiving much-needed continuing education credits during the Conference’s established dual education track, WRCCA also presented its fourth-annual Crop Consultant of the Year award and Allan Romander Scholarship and Mentor Awards.
Karl Wyant, Ph.D., director of agronomy at Nutrien and WRCCA Board Chair, presented the awards.
CCAs, PCAs, growers and industry professionals congregated on the tradeshow floor during mornings and afternoons.
CCA of the Year
The CCA of the Year award recognizes a CCA in the western region (North Valley, South Valley, Coast and Desert) of the U.S. who has shown dedicated and exceptional performance as an advisor. The ideal candidate leads others to promote agricultural practices that benefit the farmers and environment in the western region. Selection criteria includes a peer nomination process, a scope of the CCA work, special skills and abilities, professional involvement and mentorship and community involvement.
This year’s CCA of the Year winner was Allan James, technical services agronomist at Mid Valley Agricultural Services. James is from Linden, Calif. and received his bachelor’s degree, master’s degree and doctorate at Iowa State University. He’s been consulting crops for over 35 years and a CCA since 2015.
“One of the great things about Allan is the expertise, having that experience really allows him to advise on crops, water and pest issues,” Wyant said.
This year’s CCA of the Year winner was Allan James, technical services agronomist at Mid Valley Agricultural Services and CCA of eight years.
James shared some words about what being a CCA means to him.
“I started out 43 years ago as a technical agronomist with a company out of Ripon, Calif.,” James said. “And I remember about three months after it started, I went home and told my wife, ‘This is the job I’ve been looking for.’
“I love the challenge of answering questions, solving the problem,” he continued. “Sometimes you say, ‘I can’t, I don’t know.’ And that’s really the joy of working in this business.
“Growers are exceptional, they have more backbone than anyone out there, our staff is exceptional. I couldn’t do what I do without them.”
Attendees had access to 8.0 DPR hours and 12.0 CCA hours as well as CDFA FREP and Arizona PCA hours.
Mentor Awards
Tracey Emmerick Takeuchi, plant science lecturer at California Polytechnic State University, Pomona; Richard Rosecrance, Ph.D., plant science professor at California State University, Chico; and Matthew Grieshop, Ph.D., director, Grimm Family Center for Organic Production and Research, California Polytechnic State University, San Luis Obispo were this year’s mentor award recipients. They were each nominated in the South Valley, North Valley and Coastal regions, respectively.
Takeuchi plans to use the award funds to support a student learning farm with both conventional and organic production through the purchase of a small, portable rototiller and high tunnel covers. Rosecrance plans to purchase temperature/light data, enabling students to conduct empirical investigations on dynamics of these within diverse orchard settings. Grieshop plans to support undergraduate and graduate student engagement in ongoing activities being managed by the Grimm Family Center at Cal Poly.
Western Region CCA Board Chair Dr. Karl Wyant posing with the 2023 CCA of the Year and Allan Romander Scholarship and Mentor Award recipients.
Scholarship Awards
Curtis Lefler of Hanford, Calif.; Matt Young of Modesto, Calif.; Sarah Ramirez of Morgan Hill, Calif.; and Isidro Lizarraga of Yuma, Ariz. were this year’s scholarship award recipients. All had excellent track records of awards, leadership and community service as well as internship experience. They were each nominated in the South Valley, North Valley, Coastal and Desert regions, respectively.
Lefler plans to become a CCA and achieve a master’s degree in an agronomy-related field. Young plans to become a CCA this year, achieve a master’s degree in soil science and become a Certified Professional Agronomist. Ramirez also plans to become a CCA this year and pursue a position as a soil conservationist with USDA-NCS in American Somoa. Lizarraga plans to achieve a master’s degree in agronomy.
Attendance for the Crop Consultant Conference broke records again with over 600 attendees.
The recipients of this year’s scholarship and mentor awards play a vital role in the development of CCAs in the western region and will continue to educate growers and prospective CCAs in the future.
On behalf of the JCS Marketing Inc. team and Progressive Crop Consultant magazine, the editor would like to thank all that attended this year’s Crop Consultant Conference in Visalia. The conference was a huge success with another record-breaking attendance year of over 600 that enjoyed the valuable seminars, exhibitors, food and entertainment.
An educational panel on DPR’s Pesticide Roadmap for the state was a crowd favorite at the conference.
Figure 1. Next season’s grape crop from budbreak to flowering relies solely on stored carbohydrates. Early shoot and root development, flowering and even fruit set are linked to those stored carbohydrates from the postharvest period (photo by Sean Jacobs, Agro-K.)
Studies and best practice examples corroborate it: When it comes to tree and vine postharvest fertilization, including fertigation is fundamental to ensure next season’ s crop success. It is that time of year to remind ourselves the season is not over after harvest.
Why Postharvest?
Fertigating at this stage is good for the roots. After the fruits have been collected, studies show, roots become the stronger sink for carbohydrates to fuel their growth, and access to readily available essential macronutrients and micronutrients such as nitrate and potassium can boost their development.
It may seem like nothing is happening with the grapevines after the grapes are harvested, the reality is different. After the harvest, vines continue to allocate resources; from the soil, grapevines are taking up nutrients and minerals, and with the process of photosynthesis, they create carbohydrate reserves and store them in permanent wood structures (roots and trunks). Therefore, the postharvest period is one of the most important periods for nutrient uptake, and carbohydrate reserves are used by vines for respiration during dormancy and for fueling new growth the following season. Next season’s grape crop from budbreak to flowering relies solely on stored carbohydrates. Early shoot and root development, flowering and even fruit set are linked to those stored carbohydrates from the postharvest period.
Figure 1. Next season’s grape crop from budbreak to flowering relies solely on stored carbohydrates. Early shoot and root development, flowering and even fruit set are linked to those stored carbohydrates from the postharvest period (photo by Sean Jacobs, Agro-K.)
Nutrient storage is important in all permanent crops. After heavy fruit and nut loads, the tree’s nutrient reserves are significantly reduced. Postharvest fertilizer, provided leaves are still photosynthetically active, will assure the tree can reload nutrient reserves to be well prepared to support next season’s early development. Tree crops grown in cooler climates with low temperatures during dormancy in winter will be faced with low soil temperature in early springtime and therefore limited root activity, even if ambient temperature is mild. In these conditions, tree crops and grape vines mainly rely on stored nutrients in the stem and roots.
Figure 2. Seasonal nitrogen uptake in a 13-year-old Nonpareil/Monterey almond orchard (cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/N_Almonds.html).
In the case of many tree fruit and nut crops, postharvest applications through foliar or fertigation could also reduce the “on-off” years incidence, where one year of heavy fruit load is followed by a year of low fruit yield. This phenomenon may be related to depleted nutrient stocks in the tree after heavy fruit load and nutrient export with harvested fruits from the orchard, rendering the tree crops unable to support a consecutive year of abundant fruit yield.
At the early bloom and fruit initiation stage, the tree fully depends on nutrient reserves, stored in the tree itself. The most important nutrients needed to top off at this period are nitrogen (N) and potassium (K), and up to 30% of total annual application of N and K should be applied. It is important to select readily available nutrient sources such as potassium nitrate, which will provide immediately available N in the form of nitrate, while tree crops need to be replenished with K as significant amounts of K are exported with the harvested fruits from the orchard.
Figure 3. Seasonal nitrogen distribution in a 13-year-old Nonpareil/Monterey almond orchard (cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/N_Almonds.html).
In the case of almonds, nitrogen can be applied any time after hull split up until a few weeks postharvest. In earlier harvested varieties and ‘Nonpareil,’ N can be applied shortly after harvest with the first postharvest irrigation. With later varieties like ‘Monterey’ or ‘Fritz,’ the application can be made post-hull split prior to harvest. This timing matches bud development that tends to occur about two weeks after ‘Nonpareil’ harvest for most varieties. Postharvest K applications may be a reasonable strategy if you are on soil that is able to hold the K. In sandy soils, K can be leached out of the rootzone, which may create a situation of deficiency in the following year.
In the case of grapes, the period after harvest but before leaf fall is one of the best times of the season for the uptake of N and K which the vine needs along with carbohydrates to provide for the period of rapid shoot growth in the spring after budbreak. This is encouragement to deliver these macronutrients after harvest when excessive growth and the K content of the fruit is not a concern. Replacing minerals is important as they are transported off-site in the crop. Even if some of these are recycled back into the soil like with leaves or canes, that recycling is slow and inadequate to provide the needed plant nutrients.
Figure 4. The period after grape harvest but before leaf fall is one of the best times of the season for the uptake of N and K.
In Research
There are two main stages of root growth. In a rhizotron study conducted in Chile in 1993 with two table grape varieties (Flame Seedless, Muscatel), it was shown that the first (and larger) peak root growth stage takes place from budbreak to petal fall/fruit initiation. The second (and smaller) peak root growth stage takes place after fruit harvest until leaf fall (postharvest). Root development is linked to the competition for carbohydrates between roots and developing fruits. Developing fruits are stronger sinks for carbohydrates produced in the leaf than roots. Therefore, root growth and development are suppressed during fruit development growth stages. Once the fruits have been harvested, roots become the stronger sink for carbohydrates to fuel their growth. Access to readily available essential macronutrients and micronutrients, applied with fertigation during postharvest, is equally essential to support root development. The recommended dose rate of nutrients in fertigation is to be decided by plant-soil-water diagnostics.
References
“Balanced soil fertility management in wine grape vineyards.” Grant, S. Practical Winery May/June 2002.
“Best Management Practices for Nitrogen Fertilization of Grapevines.” Peacock, B., Christensen, P. and Hirschfelt, D. University of California Cooperative Extension.
“Foothill Vineyard Post Harvest Activities: FERTILIZING: Information summarized from ‘Grapevine nutrition and fertilization in the San Joaquin Valley.’” Christensen, P., Kasimatis, A. and Jensen, F. UC ANR pub. 4087 (the “black book”) now out of print.” L.R. Wunderlich, UCCE Farm Advisor. Foothill Vineyard News, Issue 9, October 2013.
“Post-harvest Vineyard Management: Growers Guide for Riverina Vineyards.” Edited by Hackett, S. and Bartrop, K.. Riverina Wine Grapes Marketing Board. March 2011.
Resources
Almond Nutrients and Fertilization: fruitsandnuts.ucdavis.edu/crops/almond
Tree Fruit Soil Fertility and Plant Nutrition in Cropping Orchards in Central Washington: treefruit.wsu.edu/orchard-management/soils-nutrition/fruit-tree-nutrition/
Potassium and Potatoes: Understanding Fertilizer-Crop Interactions
Potatoes require high levels of potassium and nitrogen to achieve optimum yields. Potassium (K) is commonly applied as potassium chloride (KCl) while nitrogen (N) is applied both preplant and in season through fertigation. Crop N is managed in season through tissue testing of potato petioles for nitrate. Petiole nitrate levels are then used as a diagnostic tool for in-season N fertilizer applications based on extension recommendations.
Methods
This research was conducted in the Columbia Basin in Hermiston, Ore. Soils in this area are sandy, which increases leaching potential for nitrate and other anions, like chloride (Cl). Previous research found that petiole nitrate levels decreased as petiole Cl increased. There was concern that there was an antagonism in uptake of nitrate and Cl and that if in-season fertilizer recommendations based on petiole nitrate levels did not consider petiole Cl, growers might be applying more N than was required for crop demand. In other words, there was a concern that petiole nitrate levels might be lower not because of low soil N, but rather because of high Cl uptake following KCl application. This project was designed to understand Cl dynamics in potato production systems.
In this project, source and timing were included as treatments while rate and placement were consistent for all treatments. Three K sources (potassium chloride (KCl); sulfate of potash, K2SO4 (SOP); and K2SO4*2MgSO4 (KMag)) were applied at 200 lb K per acre at three different times in the season. The timing of the treatment applications were 206 days prior to planting (fall preplant), 14 days prior to planting (spring preplant) and 35 days after planting (layby). Russet Burbank potatoes were planted on April 11. After planting, beds were tilled by moving soil from between the rows into the potato rows. Potato plants had emerged but not closed canopy at the time of the layby fertilizer application.
Potato petioles were collected two times in the growing season (70 and 97 days after planting) to coincide with extension recommendations for in-season fertilizer management decisions. Soil samples were collected 68 to 70 days after planting. Aboveground whole plant biomass was collected 116 days after planting and potato tubers were harvested 21 days later. Potato yield and quality metrics including specific gravity were evaluated for all treatments. These plant and soil measurements were designed to understand how much Cl plants were taking up, where in the plant the Cl was going and how Cl uptake was impacting plant N levels.
Figure 1. Effect of K fertilizer source and timing on soil (0 to 8 inches depth) extractable Cl (a), SO4-S (b) and K (c) at 70 days after planting.
Source by Timing Interaction Revealed
Soil Cl concentrations revealed a source by timing interaction. When KCl was applied in the fall, soil Cl levels were similar to those in zero K control as well as KMag and SOP treatments; however, when KCl was applied in spring or during the growing season, soil Cl was greater with KCl compared to other treatments. Plant Cl measurements followed the same pattern as soil measurements. The most likely explanation for these results was greater leaching of Cl below rooting depth with fall fertilizer application as compared to spring or in-season fertilizer applications.
Despite being in a low-rainfall area, several factors favored overwinter leaching of Cl below the root zone. First, the soil texture is sandy loam with a low water-holding capacity. Second, the timing of field operations and bed preparation relative to fall fertilizer application facilitated Cl exclusion from beds. In the fall, fertilizers were applied to flat ground. Prior to potato planting in spring, beds were created from the top 2 to 4 inches of the soil present on flat ground. Therefore, overwinter leaching of Cl below a depth of approximately 4 inches would be sufficient to move it below the potato beds. Cumulative rainfall between fall preplant fertilizer application and planting in spring was 4.25 inches, though daily precipitation was never more than 0.4 inches. From February 1 to March 18 (date of spring preplant fertilizer application), cumulative rainfall was 2 inches as compared to cumulative estimated ET of 0.83 inch, which indicates a potential for leaching. In contrast, during the interval between spring preplant fertilizer application and planting (March 28 to April 11), cumulative rainfall was 0.3 inches as compared to cumulative estimated evapotranspiration (ET) of 0.43 inches. Therefore, little or no leaching was expected between spring preplant fertilizer application and planting. Following potato planting, irrigation plus precipitation did not leach out Cl.
Figure 2. Effect of K fertilizer source and timing on petiole NO3-N (a) and Cl (b) at 70 days after planting.
Petiole nitrate concentrations were similar for all treatments at both sampling dates. Higher Cl levels in petioles with spring preplant or layby KCl application did not reduce petiole nitrate. For example, at 70 days after planting, petiole Cl was increased twofold with spring preplant or layby KCl application as compared with fall application. In contrast, petiole nitrate concentrations were similar regardless of the timing of KCl application. At harvest, crop N concentrations were similar across all treatments.
K fertilizer source and timing did not impact total or marketable potato yield. There were no significant differences for specific gravity by treatment. However, among KCl treatments, the values for specific gravity and potato yield were as follows: Fall Preplant > Spring Preplant > Layby. This suggests that higher soil and plant Cl during the growing season may have delayed tuber initiation or growth. Typically, specific gravity increases with tuber maturity.
Figure 3. Effect of K fertilizer source and timing on petiole NO3-N (a) and Cl (b) at 97 days after planting.
This experiment was designed to minimize yield differences between treatments so that nutrient movement could be evaluated without regard to plant nutrient partitioning and physiological source-sink relationships. These results indicate potato plants accumulate large concentrations of Cl when available due to KCL being applied later in the growing season. Fall KCl applications, which allowed for overwinter leaching below the root zone, resulted in the lowest soil and plant Cl concentrations when compared to other application times.
In this research, aboveground biomass and tubers were collected three weeks apart and the Cl concentration in aboveground biomass was higher than in tubers. Peak nutrient uptake in potatoes occurs during times of significant aboveground growth. Photosynthates are then translocated into potato tubers during tuber bulking, which subsequently increases water uptake into tubers. As a result, Cl concentration in the tubers is diluted and decreases as a proportion of tuber weight during this bulking stage. Standard grower practice is to leave desiccated vines in the field after harvest. The majority of plant Cl is in the aboveground biomass at the end of the season and thus Cl is added back into the soil.
In this project, we did not measure an antagonism in crop update between nitrate and Cl. Our experimental design likely minimized the interaction between N and Cl because N was applied at lower rates during peak uptake to meet crop demand. Total N concentration in aboveground biomass and potato tubers as well as nitrate in petioles were generally unaffected by K source or time of K application. In this research, petiole Cl levels were affected by K source and time of application. Concentrations increased when KCl was the K source, and as KCl was applied closer to petiole sampling date. In this project, Cl levels were always higher in petioles collected later in the year, which indicates potatoes continue to accumulate Cl throughout the growing season. Petiole nitrate levels, by contrast, were consistently lower among all treatments for the second petiole collection date. Although Cl is an essential micronutrient, it is not metabolized into plant compounds, and high concentrations of Cl are maintained in aboveground plant tissue including petioles throughout the growing season.
Figure 4. Effect of K fertilizer source and timing on Cl concentration in aboveground biomass (tops) collected at 116 DAP (a) and in tubers at harvest (b). Aboveground biomass Cl uptake (kg ha-1; right axis in “a”) was estimated based on average biomass (2780 kg ha-1). Tuber Cl uptake (kg ha-1; right axis in “b”) was estimated based on average tuber dry matter (179 g kg-1) and average tuber total yield (64 Mg ha-1).
Though there were significant differences in petiole Cl concentrations by treatment, the antagonism in uptake between N and Cl in petioles that had been documented by other researchers was not measured in this study. In this project, N was applied weekly at a uniform rate to all treatments during periods of peak uptake throughout the growing season and was thus replenished and available for plant uptake. This application method likely allowed the Cl uptake and movement to be unaffected by N availability.
Potato plants can take up Cl when it is available, and that Cl accumulates in plant tissue (particularly aboveground biomass) until harvest. Higher concentrations of petiole Cl from preplant or in-season KCl application did not affect petiole nitrate when N was applied via fertigation throughout the growing season. Fall-applied Cl was not taken up by the crop because of the opportunity to leach out of the soil used to form potato beds prior to planting. Even in a low-rainfall area, sufficient leaching of Cl below the rootzone is possible if KCl is applied far in advance of planting.
This project was funded by United States Department of Agriculture: National Institute of Food and Agriculture and Compass Minerals. Dan Sullivan worked on data analysis and publication of results. Dr. Don A. Horneck proposed this research project and died before the completion of this project. He is missed.
Figure 5. Effect of fertilizer source on S concentration in petioles (pet), tubers and aboveground biomass (tops). Petioles sampled during tuber bulking growth stage (70 and 97 days after planting), aboveground biomass at 116 days after planting, tubers at harvest. Error bars indicate standard error of the mean (n=15).
Alkaliweed (Cressa truxillensis) is a perennial herb (Figure 1a) native to California. Generally, it is found growing in natural areas, field margins and ditch banks. However, in recent years, it has been observed in agricultural areas. Alkaliweed was first reported as a problematic weed to the UCCE Fresno County in 2016. It is now being widely observed in tree nut orchards, agronomic crops, fallow fields, ditch banks and roadsides. It is more noticeable in young pistachio orchards in the southern Central Valley (Figure 1b). Standard orchard floor management practices such as between-row cultivation and herbicide applications have failed to control this species, and very little information is available on the biology, ecology and management of this species.
Figure 1. a) An alkaliweed plant and b) heavy infestation of alkaliweed in a Kings County pistachio orchard in late spring (all photos courtesy A. Shrestha.)
Common herbicides registered for use in orchards, such as glyphosate, glufosinate, salflufenacil, paraquat, 2-4 D, halosulfuron, carfentrazone, rimsulfuron and oxyfluorfen, only seem to suppress the plants for approximately 30 days before the plant starts regrowing. Treatments in pistachio orchards in Kings County showed the herbicide-treated plants regrew from new stems emerging from extensive underground root and/or shoot systems and from the aboveground parts of the treated plant. Similar observations were made in plants that had been cultivated with mechanical equipment. Such observations led us to suspect alkaliweed persists because of its dense aboveground and belowground plant parts (Figure 2a) and rhizome-like structures (Figure 2b).
Figure 2. a) Belowground plant parts and b) rhizome-like structures of alkaliweed.
While flowers (Figure 3) and seed are produced, very little is known about their contribution to invasion and spread. Also, very little is known about the germination ecology of its seeds, specifically in response to environmental stresses caused by soil pH, salinity and moisture that occur in the Central Valley. The populations in Kings County were observed in moderately alkaline and saline soils prone to summer drought.
Figure 3. Reproductive structures of alkaliweed.
Alkaliweed is stated to be a shade-intolerant plant (USDA-NRCS 2023). Our observations from 2016-18 showed it seemed to prefer and grow better in full sunlight than in shaded conditions. Plants were seen growing throughout young orchard floors that had very little canopy shading, but in older orchards they were observed mainly in the row middles and along unshaded areas of adjacent roadsides and canal banks. Therefore, we believed it was important to assess the shade tolerance ability of alkaliweed because such information could be beneficial in mitigating population spread and in the development of management strategies for this species. If flower and seed production are influenced by shaded conditions in this species, then more options become available in developing management practices to limit its sexual reproduction that contribute to seedbanks.
Although propagation of alkaliweed is primarily stated to be by seed (USDA-NRCS 2023), field observations have shown sprouting ability by underground plant parts that resemble rhizomes or stems as shown in Figure 2, see page 20. However, it is not known for certain what the reproductive potential of these structures are in alkaliweed and this needs to be studied, because limiting both seedbanks and bud banks may be necessary to effectively manage this species.
Therefore, we undertook a study on alkaliweed to 1) assess the germination of its seeds in response to environmental stresses such as pH, salinity, and moisture; 2) assess the impact of different levels of shade (full sunlight, 70% of full sunlight and 30% of full sunlight) on its aboveground growth and morphology; and 3) assess the effect of postemergence herbicides on its suppression.
Seed Germination
Seed germination experiments were conducted in a controlled-environment growth chamber at California State University, Fresno. Seed germination was tested under a range of pH solutions (5, 6, 7, 8 and 9) prepared using sodium hydroxide (NaOH) and hydrochloric acid (HCl) proportions. Germination was also tested in a range of salinity solutions measured by electrical conductivity (EC) of 0, 2.5, 5, 10, 15 and 20 dS/m (1 dS/m = 1 mmho/cm) that were prepared using laboratory-grade sodium chloride (NaCl). Furthermore, germination was tested under a range of water potential (ψ) solutions (0, -0.51, -1.88, -2.89, -4.12 and -5.56 MPa) prepared using polyethylene glycol (PEG 6000) to assess the drought tolerance of seeds for germination.
Effect of Shade on Alkaliweed Growth and Reproduction
An alkaliweed-infested roadside alongside the top of a ditch bank in Stratford, Calif. adjacent to a seven-year-old pistachio orchard infested with alkaliweed was used to study the effects of full sun and shade on alkaliweed morphology and growth. Shade tents (Figure 4) were constructed with PVC pipe frames and fitted with shade clothes representing 30% shade (70% of full sun) and 70% shade (30% of full sun). The shade tents were set up before alkaliweed plants emerged from the soil. Each treatment was replicated four times in a randomized complete block design. The photosynthetically active radiation (PAR) inside and outside the tents was taken every week between 11:00 a.m. and 1:00 p.m. using a hand-held quantum sensor. The number of plants and number of plants with flowers in the treatments were counted at the onset of flowering. The plants were harvested once five plants within a random area in each treatment plot had flowered. The plants were clipped at the soil surface, put into paper bags, and transported to the lab at Fresno State. In the lab, fresh weight of the five plants per treatment were taken, and the number of flowers and internodes on each plant were counted. The internode length on each plant was measured and recorded. The total leaf area on each plant was measured using a leaf area meter. The parts of the five plants were put together in separate paper bags for each treatment and placed in a forced-air oven and the dry weights were recorded after three days. The experiment was conducted from April to August 2019.
Figure 4. Layout of the shade study on the roadsides of the pistachio orchard in Stratford, Calif.
Postemergence Herbicides on Alkaliweed
The effect of postemergence herbicides on alkaliweed was tested by spraying actively growing plants on the edge of the road outside a pistachio orchard in Stratford on April 11, 2018. Since the plants had more of a semi-prostrate growth habit, the plants were approximately 1 to 1.5 inches tall and 6 inches in diameter at the time of the spray. The herbicide treatments included one-time applications, sequential applications and tank mixtures of herbicides (Table 1). Adjuvants were added to the herbicide treatments as recommended by each herbicide label and the solutions in all the treatments were buffered to a pH of 5.5 using BioLink® acidifier (Westbridge Agricultural Products, Vista, Calif). The herbicides were applied with a two-nozzle (Turbotwinjet 11004, Model TTJ60) spray boom using a CO2 backpack sprayer calibrated to spray 34.6 gallons/acre at 3 miles/hour. The spray pressure and spray height were maintained at 30 psi and 18 inches above the plant, respectively. Each treatment plot was 30 feet long and 3.3 feet wide. The experimental design was a randomized complete block with four replications of each treatment. The alkaliweed plants were evaluated at weekly intervals up to 28 days after treatment (DAT) for mortality on a scale of 0 to 100 where 0 was considered completely healthy without necrotic symptoms and 100 was considered entirely dead with no green tissue remaining.
Data for each of the experiments above were analyzed using analysis of variance (ANOVA) and when the analysis showed a significance at α=0.05, the means were separated using Fisher’s Least Significant Difference tests. Regression analysis was also used for the germination studies.
Effect of Environmental Factors on Seed Germination
Alkaliweed seeds were moderately drought-tolerant as germination was 68.5% at -0.51 MPa and 12% of the seeds germinated at a fairly high negative water potential of -1.09 MPa. There was no germination beyond water potential values of -1.09 MPa. The water potential level that reduced seed germination by 50% was estimated as -0.78 MPa. For comparison, in field bindweed (Convolvulus arvensis), another plant of the Convolvulaceae family, the water potential that reduced germination by 50% was estimated as -0.4 MPa (Tanveer et al. 2013). Therefore, it appears alkaliweed seeds are more tolerant to water potential stress than field bindweed during germination, enabling it to germinate in the semiarid regions of the Central Valley under fairly dry conditions.
Alkaliweed seeds were very tolerant to salinity (sodium chloride) stress at germination as approximately 24% of the seeds germinated at a very high EC level of 20 dS/m, although percent germination was significantly lowered at EC levels higher than 10 dS/m. The salinity level that reduced seed germination by 50% was estimated as 15.3 dS/m. Again, there are no studies that have reported the effect of salinity levels on alkaliweed, but in field bindweed Tanveer et al. (2013) reported similar tolerance to salinity stress. Therefore, alkaliweed can germinate in the high-salinity regions of the westside of the Central Valley.
Unlike water potential and salinity, germination of alkaliweed seeds was not affected by the range of the pH levels tested. Germination was similar at all pH levels (5 to 9) and ranged from 76% to 84%, indicating this species has a wide range of adaptation to pH levels during germination. Although more than 80% of the seeds germinated at a pH level of 5, it is not known if the plants would grow and reproduce at this pH level because the optimum pH range for growth of this species is reported as 6.8 to 9.2 (USDA-NRCS 2023). Again, there are no published studies on the germination of alkaliweed seed in response to pH, but Tanveer et al. (2013) reported that field bindweed germinated at a pH range of 4 to 9 but the optimum pH was 6 to 8. Therefore, it appears that alkaliweed can germinate in the alkaline and acidic soils of the Central Valley.
Effect of Shade on Growth of Alkaliweed
Shade levels influenced the morphology, growth and reproductive potential of alkaliweed plants. The PAR taken close to noon in the treatment plots during the experiment, on average, ranged from 1700 to 2000, 1000 to 1300 and 500 to 700 µmol m-2 s-1 in the full sun, 30% shade and 70% shade, respectively. Although the total aboveground biomass and number of internodes on the stem were not affected by shade level, other morphological characters showed that this species was not a shade-tolerant plant and that plants exhibited efforts to adapt to shade. For example, the length of internodes on the stem increased as the level of shade increased. The average length of the internodes in the plants growing in the full sun was approximately 1.3 inches whereas at 70% shade it was approximately 3.5 inches. Similarly, the total leaf area per plant was higher in the plants grown in the shade than in the full sun. Leaf thickness was not measured in the study. However, it is suspected that leaves on the plants growing in the shade were comparatively thinner than on those growing in the full sun because thin leaves are an adaptation strategy of shade-intolerant plants when growing under shade (Glime 2017). Similar results were reported in field bindweed where internode length and total leaf area were lesser in plants grown in the full sun than those grown under shade (Gianoli 2001). However, field bindweed is more of a viny plant than alkaliweed.
Although the plants growing in the shade had similar aboveground biomass as those in the full sun, none of the plants in either the 30% or the 70% shade treatments produced any flowers for the duration of this study. Therefore, it appears that reproduction can be severely inhibited in alkaliweed by shade, and use of shading strategies may be an effective management method to reduce sexual reproduction of this species.
Effect of Postemergence Herbicides on Alkaliweed
Plant mortality differed between the herbicide treatments at each evaluation date (Table 2). Initially, saflufenacil (alone) and the tank mix of glyphosate + saflufenacil + glufosinate looked promising as more than 80% of the plants showed injury symptoms at 7 DAT and the plants appeared to be dying. However, by 28 DAT, the plants regrew, and the mortality was reduced to 50% and 53%, respectively, for the two treatments. This level of control would not be considered acceptable to a grower managing alkaliweed. None of the herbicide treatments provided acceptable control as the mortality rate was 20% or less in most cases. It was expected that the sequential application treatments would work better but it was not the case. Sequential applications of glyphosate and carfentrazone provided 43% control whereas that of glyphosate and paraquat provided only 15% control. Although appropriate adjuvants were applied in all the treatments, the postemergence herbicides failed to control the plants which is perhaps due to reduced contact, retention and absorption of the herbicides because of the hairiness of the alkaliweed plants as observed under a microscope (Figure 5). Even the leaves of small plants were observed to be hairy. Also, it is not known if the regrowth is because of adequate levels of stored carbohydrates or growth of new stems (aboveground or belowground) as discussed earlier. Therefore, alkaliweed control may not be feasible using postemergence herbicides alone. It has been reported that 2,4-D can provide some level of control but in-season use of this herbicide in orchards could be a concern due to phytotoxic effects on the trees.
Our study showed alkaliweed seeds could germinate in moderate drought and high salinity conditions under a range of soil pH. The species was not very shade-tolerant, and no reproductive structures were observed in the plants growing in the 30 and 70% shade levels. None of the postemergence herbicides provided adequate control of the plants. Therefore, an integrated management plan which includes multiple tactics needs to be developed for managing alkaliweed in Central Valley orchards. Complete details on this study are available at mdpi.com/2392752.
Figure 5. Microscopic images showing the presence of hairs on the leaves of alkaliweed.
We would like to thank Mr. Kevin Brooks, PCA, for the wealth of information provided on alkaliweed.
References
Gianoli E. 2001. Lack of differential plasticity to shading of internodes and petioles with growth habit in Convolvulus arvensis (Convolvulaceae). Int J Plant Sci 162:1247–1252. https://doi.org/10.1086/322950.
Glime J. 2017. Light: Adaptations for Shade. In: Glime, J. M. Bryophyte Ecology. Volume 1. Physiological Ecology. 9-2-1, http://digitalcommons.mtu.edu/bryophyte-ecology.
Tanveer A, Tasneem M, Khaliq A, et al. 2013. Influence of seed size and ecological factors on the germination and emergence of field bindweed (Convolvulus arvensis). Plant daninha 31(1) https://doi.org/10.1590/S0100-83582013000100005.
USDA-NRCS, 2023. Conservation plant characteristics, Cressa truxillensis Kunth, spreading alkaliweed, CRTR5. https://plantsorig.sc.egov.usda.gov/java/charProfile?symbol=CRTR5.
Mechanical Leaf Removal is More Effective than Regulated Deficit Irrigation to Improve Fruit Quality While Maintaining Yield
Berry sugar and anthocyanin accumulation are key factors in determining the fruit quality of red wine grapes in the San Joaquin Valley (SJV), where >70% of California wine grapes are grown (California Grape Crush Report 2022). Hot climates are not ideal for red Bordeaux cultivars such as Cabernet Sauvignon and Merlot as anthocyanin accumulation is inhibited (Figure 1).
Figure 1. Overly vigorous vine due to abundant winter precipitation and overirrigation (all photos courtesy G. Zhuang.)
However, fruit quality might be improved with certain management practices, including deficit irrigation and leafing. Previous research in the SJV demonstrated that moderate irrigation deficits can improve grape yield and quality in addition to saving water (Williams 2012). Mild or moderate irrigation deficits promote yield formation due to increased bud fruitfulness and decreased fungal disease pressure. Sustained deficit irrigation (SDI) of 70% to 80% evapotranspiration (ETc) was found to balance economically sustainable yield, fruit quality and water-savings goals (Williams 2010). Abundant winter precipitation and overirrigation cause grapevines to grow excessively, shading the fruit, directly reducing quality and favoring the development of fungal diseases (Mendez-Costabel et al. 2014) (Figure 2).
Figure 2. Heavy powdery mildew infestation on Chenin Blanc (top) and botrytis bunch rot on Pinot Gris (bottom).
Years like 2023 might remind growers that managing water and canopy size to improve canopy microenvironment and enhance spray coverage will reduce fungal disease pressure (Figure 3). However, severe water deficits pre-veraison significantly impair grapevine vegetative and reproductive growth, photosynthesis and fruit maturity (Levin et al. 2020).
Figure 3. Leaf removal around grape cluster (top). Spray coverage increases with leaf removal (bottom).
Removing leaves in the fruit zone is another beneficial practice growers may do to improve fruit quality. Leafing increases fruit exposure which may directly improve fruit quality, create a microenvironment that discourages powdery mildew and bunch rots, and improve spray coverage (Austin and Wilcox 2011) (Figure 4). Leaf removal is most practiced in cool climates as overexposure can easily reduce fruit quality in a hot climate. However, studies on leaf removal in a hot climate also showed similar benefits as reported in cooler climates (Cook et al. 2015). As with deficit irrigation, the timing and intensity of fruit zone leaf removal determines the potential impact on grapevine yield and fruit quality at harvest. In a cool climate, basal leaf removal prior to bloom may reduce berry set, thus lowering yield (Acimovic et al. 2016). Effects on berry set depend on the extent of leaf removal and the weather (Frioni et al. 2017). In hot climates, mechanical fruit zone leaf removal prior to bloom had no effect on berry set or yield (Cook et al. 2015). In addition to the potential to reduce set in cool climates, leaf removal prior to bloom can increase berry total soluble solids, anthocyanin content and berry aroma compounds (Ryona et al. 2008). Recently, mechanical fruit zone leaf removal has gained popularity due to labor shortage and increased labor cost in California (Kurtural and Fidelibus 2021). Years like 2023 which came with abundant winter precipitation, delayed harvest and cool temperatures might require additional fruit-zone leaf removal to open the canopy and increase spray coverage to help control fungal diseases.
Figure 4. Clemens roll-over leaf plucker with a sickle-bar sprawl clipper (top) and mechanical leaf removal at full bloom of Cabernet Sauvignon (bottom).
Three-Year Field Study
Aiming to find the “sweet spot” of water management and leaf removal on yield, sugar and anthocyanin accumulation of red wine grape in hot climates, we conducted a three-year field study on Cabernet Sauvignon grown in Madera as Cabernet Sauvignon is believed to be one of the most challenging varieties to be grown in the SJV due to lack of berry color at harvest.
The experiment was conducted in a commercial vineyard located in Madera on fine sandy loam soil. 10-year-old Cabernet Sauvignon vines on Freedom rootstock with 4’ ´ 10’ spacing and Northeast-Southwest row orientation were used for the experiment. The grapevines were quadrilateral cordon trained with a 24-inch cross-arm to 48-inch height above vineyard floor with a pair of catch wires above the cordons. A two (deficit irrigation) × three (leaf removal) factorial split-plot design was applied for three seasons: 2018 through 2020. Two irrigation treatments were applied: 1) sustained deficit irrigation (SDI): water was maintained at 80% of weekly crop evapotranspiration (ETc) through the growing season; 2) regulated deficit irrigation (RDI): water was maintained at 50% ETc from berry set to veraison then switched back to 80% ETc until harvest. ETc was calculated using the equation of ETc = ETo × Kc (Williams 2010). On top of irrigation treatments, we applied three timings of mechanical leaf removal: 1) bloom, 2) berry set and 3) no leaf removal. Leaf removal was applied to both sides of the canopy using a roll-over leaf plucker with a sickle-bar sprawl clipper adapted for a sprawling-type canopy (Model EL-50, Clemens Vineyard Equipment, Woodland, Calif.).
Results and Discussion
RDI reduced yield by 15% compared to SDI mainly due to smaller berries and clusters (Tables 1 and 2). Leaf removal did not significantly affect yield. Our result confirms that severe water deficit, like 50% ETc, pre-veraison, can result in significant yield loss. Contradictory to the previous field observation, bloom leaf removal had no effect on yield, and growers should be less worried about yield loss due to bloom leaf removal than severe deficit irrigation.
Berry soluble solids (Brix) were affected mainly by irrigation treatments in our study. RDI consistently reduced soluble solids each year (Table 2). Interestingly, we found that the effect on Brix depended on the interaction of leaf removal and water management (Table 3). Leaf removal increased Brix when vines were not water stressed or mildly stressed like when SDI was applied whereas leaf removal reduced Brix when vines were severely water stressed like when RDI was imposed. This implies to growers that if sugar is your biggest concern, you should water vines maintaining mild or moderate vine water stress and remove fruit-zone leaves.
Berry anthocyanin content is critically important for red wine grapes. RDI increased berry anthocyanins by 14% in comparison of SDI, and bloom and berry set leaf removal increased anthocyanins by 19% and 13%, respectively, compared to no leaf removal control (Table 2). This means the 14% increase in anthocyanin concentration from the RDI treatment is proportional to the decrease in berry weight and yield. So, there is no net gain of anthocyanins per berry associated with the RDI irrigation treatment. Bloom leaf removal increased anthocyanins by nearly 20% with no yield reduction and that means bloom leaf removal provides a net gain of anthocyanins per berry.
Bloom leaf removal was more effective than pre-veraison RDI at improving berry Brix and anthocyanins without adversely affecting yield. Given the significant reduction on yield from severe deficit irrigation and the low economic return per ton of fruit in the SJV, bloom mechanical leaf removal coupled with SDI of 80% ETc could be a useful practice for SJV growers.
References
Acimovic, D., Tozzini, L., Green, A., Sivilotti, P., and Sabbatini, P. (2016) Identification of a defoliation severity threshold for changing fruitset, bunch morphology and fruit composition in Pinot Noir. Australian Journal of Grape and Wine Research, 22: 399– 408. doi: 10.1111/ajgw.12235.
Austin, C and Wilcox, W. (2011) Effects of Fruit-Zone Leaf Removal, Training Systems, and Irrigation on the Development of Grapevine Powdery Mildew. Am J Enol Vitic. June 2011 62: 193-198.
Cook, M., Zhang, Y., Nelson, C., Gambetta, G., Kennedy, J., Kurtural, K. (2015) Anthocyanin Composition of Merlot is Ameliorated by Light Microclimate and Irrigation in Central California. Am J Enol Vitic. 66: 266-278.
California Sustainable Groundwater Management Act (SGMA) 2014 Sustainable Groundwater Management Act (SGMA) (ca.gov)
California Grape Crush Report 2022, USDA National Agricultural Statistics Service (NASS). USDA – National Agricultural Statistics Service – California – Grape Crush Reports
Frioni, T., Zhuang, S., Palliotti, A., Sivilotti, P., Falchi, R. and Sabbatini, P. (2017) Leaf Removal and Cluster Thinning Efficiencies Are Highly Modulated by Environmental Conditions in Cool Climate Viticulture. Am J Enol Vitic. 68: 325-335.
Kurtural, K and Fidelibus, M. (2021) Mechanization of Pruning, Canopy Management, and Harvest in Winegrape Vineyards. Catalyst: Discovery in Practice. 5: 29-44.
Levin, A., Matthews, M., and Williams, L. (2020) Effect of Preveraison Water Deficits on the Yield Components of 15 Winegrape Cultivars. Am J Enol Vitic. 71: 208-221.
Mendez-costabel, M., Wilkinson, K., Bastian, S., Jordans, C., Mccarthy, M., Ford, C., and Dokoozlian, N. (2014) Effect of increased irrigation and additional nitrogen fertilisation on the concentration of green aroma compounds in Vitis vinifera L. Merlot fruit and wine. Australian Journal of Grape and Wine Research. 20:80–90.
Ryona, I., Pan, B., Intrigliolo, D., Lakso, A., and Sacks G. (2008) Effects of Cluster Light Exposure on 3-Isobutyl-2-methoxypyrazine Accumulation and Degradation Patterns in Red Wine Grapes (Vitis vinifera L. Cv. Cabernet Franc). Journal of Agricultural and Food Chemistry 56 (22), 10838-10846.
Williams, L. (2010) Interaction of rootstock and applied water amounts at various fractions of estimated evapotranspiration (ETc) on productivity of Cabernet Sauvignon. Australian Journal of Grape and Wine Research. 16:434–444.04
Williams, L. (2012) Interaction of applied water amounts and leaf removal in the fruiting zone on grapevine water relations and productivity of Merlot. Irrig Sci. 30: 363-375.
Williams, L. (2014) Effect of Applied Water Amounts at Various Fractions of Evapotranspiration on Productivity and Water Footprint of Chardonnay Grapegrapevines. Am J Enol Vitic. 65: 215-221.
Timely and Efficient Nutrient Management for Strawberry
Production on the Central Coast
Strawberry yields have been higher in California than most other parts of the U.S. since the early 1950s. Strawberries are a high-value, highly perishable fruit, and as such, the industry developed around large populations such as Los Angeles and Orange counties, near San Francisco and Sacramento, and the San Joaquin Valley where the berries could easily be distributed. The mild climate allows for strawberry harvests to extend over a long period of time (April until November). In recent years, with a multitude of early varieties, the harvest has begun as early as late January.
After World War II, strawberry production in California increased rapidly. This allowed the Salinas Valley to become the largest commercial strawberry producing area in the world, with successful production and marketing of frozen strawberries being a primary factor in California’s dominance. Strawberry production acreage continues to grow each year, with fresh strawberries being 75% of the production and the other 25% being frozen and processed berries. Currently, Watsonville, Salinas, Santa Maria, Oxnard and Orange County contain the most strawberry acreage in production (Figure 1). Growth stages of strawberry plants are illustrated in Figure 2, ranging from preplant to harvest.
Figure 1. Watsonville, Salinas, Santa Maria, Oxnard and Orange County contain the most strawberry acreage in production.
Preseason
Prior to the strawberry growing season, it is always important to take a representative soil test to determine soil type, electrical conductivity (ECe), pH, cation exchange capacity (CEC), quantity of exchangeable cations and organic matter content. Local labs provide this service and can be contracted to take samples, run tests and provide recommendations to growers. Here is where the CCA training comes into play. Knowing the types of nutrients essential for plant growth and in what quantities is an important skill acquired through CCA stewardship. Similarly, you will want to request laboratory tests for nitrate (NO3-N), dissolved solids, salts, bicarbonates, pH and ECe for the irrigation water that will be applied to the crop during the season.
Figure 2. Growth stages of strawberry plants from preplant to harvest.
Many growers use preplant applications of fertilizer applied at bed shaping to ensure the newly transplanted plants have adequate nutrients. Controlled/slow-release fertilizers release nutrients gradually into the soil as the plant needs them as opposed to conventional fertilizers which are available immediately upon application. The timing of preplant applications is important as studies have shown most of the nitrogen (N) applied at preplant was released before the plants were large enough to utilize the available N. Phosphorus (P) and potassium (K) are much less mobile than N and are better utilized when applied during bed shaping.
At Planting
At planting, it is essential to maintain a large enough reservoir of exchangeable N, P and K within the soil to allow for optimal growth of the newly transplanted strawberry plant. The young plants have a limited root system and will not require large amounts of nutrients at this point in the season. A soil test value for nitrate developed by T.K. Hartz shows that a value of 20 mg/L is adequate to supply NO3-N to the young plant. Phosphorus is an essential element in plants as it is a component of nucleic acids (Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)), energy-containing molecules (adenosine triphosphate (ATP)) and nicotinamide adenine dinucleotide phosphate (NADP)) and cell structure (phospholipids). Phosphorus availability is essential for root growth and cell multiplication as the new transplants take root in the soil. Mycorrhizal fungi applications have been shown to increase phosphorus supply to the plants through a symbiotic relationship where the plant essentially trades sugars for phosphorus. This is of course a very complex process and not as simple as it sounds.
Figure 3. Nitrogen deficiency in strawberry plants. If not enough N is applied, the canopy will not grow large enough to protect the fruit from the sun.
Early Season
As the season progresses and the strawberry plants grow larger, a continuous supply of N, P and K must be maintained. While the plant is still in a vegetative state, additions of N need to be monitored closely. Not enough N and the plant will show deficiency symptoms similar to (Figure 3). If not enough N is applied, the canopy will not grow large enough to protect the fruit from the sun. Too much N and the plant will continue vegetative growth and continue to produce leaves and only small fruit. If the canopy is too large, more nutrients are required to maintain the plant’s structure and the plant will have a difficult time providing adequate-sized fruit for harvest.
Phosphorus applications are essential to allow for crown split, which aids in the determination of the plant’s berry production. Phosphorus deficiency in strawberries begins with a slight purple discoloration which can be mistaken for twospotted spider mite infestation, so monitoring and tissue testing is critical. As the P deficiency progresses, we see reddening of the lower leaves (Figure 4). The crown of the strawberry plant is the short, thick stem which has many growing points slightly above the ground. It is the base of the plant from which leaves, fruit, runners and roots all grow. The more crowns, the more potential berries. Potassium is also essential as it controls stomatal apertures and allows the plant to regulate the transpiration occurring.
Figure 4. Advanced phosphorus deficiency in strawberry. Symptoms begin with a slight purple discoloration which can be mistaken for twospotted spider mite infestation.
Mid to Peak Season
As flowers begin to develop and the plants move out of vegetative growth, it is important to continue to supply N, P and K in larger quantities. Flower and fruit development will require P for cell multiplication and energy as the fruit develops rapidly. Phosphorus will also be important to plants for continued root growth as well as inducing new flowers to be produced within the crown. Calcium (Ca) concentrations available to the plants become more important as the cell wall strength of fruit relies heavily on both Ca and K to provide firmness of the strawberry fruit. A significant portion of the fertilizer budget for the season is taken up by the plants from April to mid-September, reaching approximately 1 lb N/acre per day. This can be used to determine rough application rates of N, but keep in mind that the plant is only one of the intermediate destinations of nutrients in the soil. Microbial populations can take nutrients into their biomass, essentially removing them temporarily from the available nutrient pool. In addition, exchange sites on soil particles and organic matter can further limit nutrient availability. A more descriptive guideline for fertilization of California strawberries can be found at Geisseler.ucdavis.edu/Guidelines/Strawberry.html, which is a collaboration between California Department of Food and Agriculture (CDFA), the Fertilizer Research and Education Program (FREP) and UC Davis. Be advised that a routine soil test such as a saturated paste extract is a good reference point for an in-season fertilizer assessment but will require interpretation on a field-by-field basis. Similarly, routine tissue testing is essential to ensure optimal uptake of macronutrients and micronutrients.
Late Season
As the season progresses and fruit is harvested from the field, N, K and Ca become more essential to functions like stomatal opening and firmness of the fruit. As the plant ages and the season progresses, more salt builds up near roots, the plant is much larger than at the beginning of the season and environmental conditions such as wind and sun take a toll on the plant. Additions of potassium and some seaweeds have shown to aid the stress of the plant. Ca additions keep cell walls from become weak and flaccid. Monitoring of harvest speeds toward the end of the season is used to ensure profitability of strawberry production, especially as quality of fruit declines and diseases such as botrytis and mildew increase.
Overall, every season has its highs and lows, booms and busts in the market and environmental effects that are out of a grower’s control. The aspects that must be focused on are timely and efficient applications of the correct nutrients and pesticides, from the right source, with the right quantities at the correct growth period (right nutrient sources, right rate, right place, right time).
Dates (Phoenix dactylifera L.), one of the world’s oldest cultivated fruits, originated in the Middle East, with its distribution extending to the U.S. in the last century. The geographical distribution of commercial date production is limited to arid and semi-arid regions where there is not abundant water supply. The low desert of California with nearly 11,000 acres of date palms is the major date production area within the U.S. followed by Arizona (Montazar et al. 2020). Since the date industry is currently economically successful and robust in California, date production is expected to increase as many new groves have been planted in recent years and more are currently being planted.
The date palm is drought tolerant; however, more accurate irrigation scheduling and water management during its flowering and fruiting season is critical for healthy date palms and high-quality fruit production. Date palm growers have started to adopt the use of microirrigation, but in many instances, irrigation management is based upon data developed decades ago in flood-irrigated orchards.
Figure 1. A drip irrigated date palm (top) and an integrated drip-flood irrigated date palm (bottom) in the Coachella Valley.
An irrigation study was conducted to acquire relevant information on crop water consumption and develop more accurate crop coefficients values for date palms in California. Extensive data collection was carried out in six mature date palm orchards in the Coachella and Imperial valleys over a three-year period. The experimental orchards represent various soil types and conditions, irrigation management practices, canopy features and the most common date cultivars in the region (‘Medjool’ and ‘Deglet Noor’). The orchards have relatively heterogeneous soil; however, the dominant soil texture varies from sandy loam to silty loam and silty-clay loam. A combination of surface renewal and eddy covariance equipment (flux tower, Figure 2) was utilized to measure actual crop evapotranspiration (ETa) at each site. This article provides some effective irrigation and water management tips in California date palms based on the findings of this study.
Recent Advances in Date Palm Water ManagementFigure 2. Flux tower set up at one of the experimental sites located in Thermal, Calif. An aerial view of the tower from a distance (top) and a ground view of the tower (bottom).
Both micro/drip and flood irrigation are common practices in the low desert region, and some growers, who have installed microirrigation systems in their orchards irrigate their date palms through an integrated micro-flood irrigation system (Figure 1). The results of our recent date palm irrigation management survey demonstrated 31% of grower responders use only flood irrigation, 19% use only microirrigation and 50% follow an integrated micro-flood irrigation management approach. The survey also illustrated drip irrigation systems dominate microirrigation systems, with nearly 88% of grower responders reporting using drip irrigation and 12% using microsprinkler irrigation.
Consumptive Water Use in Date Palms
The results of this study demonstrated considerable variability in date palm consumptive water use (Figures 3 and 4). The cumulative date palm water use over a 12-month period across the six sites ranged from 51.7 in. (site 5) to 59.1 in. (site 3) with a mean daily ETa of 0.28 in d-1 in June-July and 0.04 in d-1 in December at the site with the highest crop water consumption.
Figure 3. Cumulative date palm actual evapotranspiration or consumptive water use (ETa) at the experimental sites over a 12-month study period (May 2019 to April 2020).
The results revealed clearly that water consumption of date palms varies significantly depending upon site-specific conditions. Various factors may influence date palm crop water use including irrigation management practices, salinity and/or soil differences, groundwater table and ground shading or canopy cover (and tree height), this last providing a good estimation of canopy size/volume and the amount of light that it can intercept. For instance, the cumulative consumptive water use over the 12-month period was 58.8 in. in a non-salt-affected sandy loam soil date palm under flood irrigation (site 4) with an average density of 50 trees per acre and an average canopy cover and tree height of 81% and 36.1 ft., respectively. In comparison, the cumulative annual consumptive water use was determined to be 51.7 in. in a silty clay loam saline-sodic date palm (site 5 under an integrated microsprinkler/flood irrigation system) with an average canopy cover of 55%, density of 60 trees per acre and tree height of 24 ft.
Figure 4. Daily actual evapotranspiration at sites 3 and 5 over the 12-month study period (May 2019 to April 2020).
Crop Coefficient Values for Date Palms
The results indicate that there is substantial difference in crop coefficient (Ka) values of date palms, both spatially and temporally (Figure 5). For instance, at site 4, the average monthly crop coefficient value varied between 0.64 in December and 0.88 in June. Date trees at this site experienced mild to moderate water stress during July, but soil moisture was maintained at a desired level during the remainder of the study period.
Figure 5. Calculated monthly actual crop coefficient (Ka) values at the experimental date palms over the 12-month study period. The observed daily actual evapotranspiration (ETa) and Spatial CIMIS reference evapotranspiration (ETo) in each of the experimental date palms were used to compute the monthly Ka values.
The soil types and conditions at sites 2, 3 and 4 were similar, and the canopy features were relatively similar as well. Both sites 3 and 4 had a density of 50 plants ac-1, whereas the density was 52 plants ac-1 at site 2. All three sites had the ‘Deglet Noor’ date cultivar. Slight differences were found among the monthly crop coefficient values of these orchards that were likely related to irrigation management differences. An integrated irrigation system consisting of drip and flood irrigation was used at sites 2 and 3. Both sites are considered fully irrigated orchards over the study period with the water applied of 7.7 ac-ft/ac at site 2 and 7.9 ac-ft/ac at site 3, with relatively high soil water availability the entire season. The average Ka values for the 12-month period were 0.81, 0.82 and 0.81 at sites 2, 3 and 4, respectively. Within the year, the monthly range of values was from 0.63 (December) to 0.90 (June) at site 3. These values likely represent the ‘potential’ Kc values for the date palms since the applied irrigation water in these orchards were 50% to 60% higher than the measured ETa and both soil moisture and canopy temperature data suggested that no water deficit occurred over the 12-month period.
Figure 6. Whole-soil-profile representations of mean ECe (electrical conductivity of the saturation extract) distribution of observed values at six experimental date palm sites (left) and the relationship of seasonal actual evapotranspiration and mean annual actual crop coefficient (Ka) versus electrical conductivity of the saturation extract (ECe) (right). The average ECe of the entire soil profile (4 ft. depth) from the whole soil samples at each date palm site were used to represent the average ECe of crop root zone in each of the experimental sites.
The monthly Ka value varied from 0.62 in November to 0.75 in June at site 5. This orchard is regularly irrigated by micro-sprinkler and occasionally flood irrigated to leach out heavy salt accumulation in the entire soil profile. Across the six sites, sites 3 and 5 had the highest and lowest Ka values averaged over the 12-month period, respectively. An average 12-month Ka value of 0.70 was obtained at site 5, which is nearly 17 % lower than the average 12-month Ka value of site 3. These sites have the same date cultivar (Deglet Noor); however, site 5 had a higher planting density and smaller trees. The reduction of tree growth at site 5 is likely associated with the physiologic adjustment of trees to the long exposure to high salinity-sodicity environments.
Soil Salinity and Date Trees’ Growth
Soil salinity varied considerably amongst the experimental sites (Figure 6, see page 12). The mean ECe (soil electrical conductivity) at the experimental sites showed that while the entire soil profile is saline at the site close to the Salton Sea (site 5, average ECe of the top 4 ft. of the soil > 12 dS m-1), relatively low values of ECe (average ECe of the top 4 ft. of the soil < 5 dS m-1) were observed within the crop root zone at the other experimental sites. The soil particle size distribution at site 5 has higher clay content below the topsoil than the other sites, which along with a high content of soluble salts and high soluble sodium resulted in both water penetration and subsurface drainage problems.
To quantify the impacts of salinity on date palm crop water use, the relations of cumulative ETa and mean annual actual crop coefficient as a function of ECe were derived. Inverse relationships were found between the seasonal actual ET and ECe; and between the mean annual Ka and ECe (Figure 6b). The average ECe of the entire soil profile (4 ft. depth) from the soil samples at each date palm site were used in this analysis to represent an average ECe for the corresponding orchards. As was mentioned, other drivers are involved in ETa and Ka values including canopy features and cultivars, soil types and irrigation management practices. These parameters do not directly contribute to the observed linear relationships; however, they indirectly influence the results. For instance, the reduced vegetative growth at site 5 may have resulted from salinity and drainage issues and the soil properties. The soil is categorized as “silty loam” with silt content greater than 50% at the top 1.2 m, and therefore, it has a very low infiltration rate. Average weight of date fruits was 31% lower at site 5 in compared with site 4 (both are ‘Deglet Noor’ cultivar).
Earlier studies indicated all aspects of date palm vegetative growth may negatively respond to salinity including the rate of production of new leaves and the size of the leaf canopy Zapata and Martinez-Cob 2002; Tripler et al. 2007). The percentage of light interception was 30% lower in the date palm irrigated by saline water (15.0 dS m-1) in a recent study (Al-Muaini et al. 2019).
Recommendations
Date palms need variable amounts of irrigation water depending on time of year, canopy cover percentage and tree height, soil types and conditions, and irrigation management. To sustain date production in the desert region, growers need to integrate microirrigation and flood irrigation together. It helps to fill the soil profile for this deep-rooted tree crop specifically at the time that drip irrigation does not have the capacity to accomplish this. During mid-June to early July, one might need to apply more than 100 gallons per day per tree. Depending on the capacity of the microirrigation system, it would be beneficial to have one flood irrigation during this period. Another flood irrigation during early season (March) is also recommended. We need to keep in mind that effective irrigation management in the desert environment is different than other regions. In the desert environment, irrigation needs to maintain crop water needs and soil salinity at the same time even for an adapted and stress-tolerant crop such as date. The two or three flood irrigation events (depending on the soil types and conditions) integrated with drip irrigation can maintain crop water needs and salinity and optimize the economic benefits of date production in the low desert region.
Growers may use the crop coefficient values developed by this study along with CIMIS ETo data to calculate crop water needs in different times of year. It is highly recommended that growers monitor soil moisture at least at the depth of 1 to 2 ft. Soil moisture at the depth of 1 to 2 ft. is a good indicator of soil water availability to date palms under microirrigation (a threshold of 25 to 30 centibar could be considered for the sandy loam soils in the Coachella Valley.)
References
Montazar, A., Krueger, R., Corwin, D., Pourreza, A., Little, C., Rios, S., Snyder, R.L. 2020. Determination of Actual Evapotranspiration and Crop Coefficients of California Date Palms Using the Residual of Energy Balance Approach. Water, 12 (8), 2253.
Zapata, N., Martínez-Cob, A. 2002. Evaluation of the surface renewal method to estimate wheat evapotranspiration. Agric. Water Manage., 55(2), 141–157.
Tripler, E., Ben-Gal, A., Shani, U. 2007. Consequence of salinity and excess boron on growth, evapotranspiration and ion uptake in date palm (Phoenix dactylifera, L., cv. Medjool). Plant and Soil, 297:147–155.
Al-Muaini, A., Green, S., Dakheel, A., Abdullah, A., Abou-Dahr, W., Dixon, S., Kemp, P., Clothier, B. 2019. Irrigation management with saline groundwater of a date palm cultivar in the hyper-arid United Arab Emirates. Agric. Water Manage., 211 (1): 123-131.
Figure 1. Utilizing products or a blend of multiple products that provide soil health-like properties for specific soil and crop responses is a newly emerging idea.
Tank mixing, the process of combining multiple crop protection chemicals, adjuvants or fertility products into the same tank, is a well-known practice. We all understand the benefits of reduced passes across the field, increasing efficiency of your applications and saving precious time. However, it’s time to shift our mindsets and tanks into applying old techniques to new concepts. The concept I am referring to is soil health. You may be thinking, ‘This is not a new concept’; however, utilizing products or a blend of multiple products that provide soil health-like properties for specific soil and crop responses is a newly emerging idea (Figure 1).
Figure 1. Utilizing products or a blend of multiple products that provide soil health-like properties for specific soil and crop responses is a newly emerging idea.
For this article, I will refer to products currently classified as biostimulants, biologicals and carbon-based products as “soil health” products. Products tailored for impacting specific soil health properties are more readily available than ever, and, frankly, this flooding of the marketplace creates much confusion among end users on performance expectations. From my own experience, I have encountered frustrated growers with numerous concerns such as, ‘These products don’t work for me’, ‘There is too much variability,’ or ‘I am unsure of what products I need.’ These are valid concerns; however, there may be some very simple solutions to addressing these problems (how we mix them in the tank or apply them to the field). When incorporating these soil health products, addressing a few basic points before getting started can help ensure the results we hope to achieve in the field. These include:
How can I understand the mode of action or the primary function of the product?
What is the soil health problem or challenge/s in your field?
Which soil health or blend of soil health products are available for my desired results?
How do I ensure my soil health blend is properly stored and tank mixed to achieve optimum success in the field?
Soil Health Products
Simply put, soil health products are inputs that provide soil health-like properties. To help break this down, let’s separate these products into two categories: living biologicals and non-living soil health products. Living biologicals are just what you think they are: The products that contain living fungi and/or bacteria that can be applied to the soil. Non-living soil health products encompass things such as enzymes, humic substances, microalgae and other microbial foods, macroalgae like seaweeds and kelps, and biochars to name a few. Keep in mind that while we can break them into two simple categories, it doesn’t mean these products are the same within each category. On the contrary, each of these products has a different mode of action and provides a different outcome when applied to the soil. To help demonstrate this, Table 1, shows a condensed list of products with their corresponding mode of action. When we think of these products, we usually think of them as a standalone application or a single addition into our ag chemical tank mixes; this is where things are about to get shook up (pun intended).
Table 1
As the presence of soil health products grows in the marketplace with a predicted 10% increase over the next eight years, there have been increasingly more research studies evaluating the synergies or complementary effects of combining products. The main takeaway from this research reveals that mixing these different products together can give growers the benefit of multiple different modes of action that optimize results. These findings demonstrate the right combination of products achieves better or higher results than acting alone. However, this information should be taken with caution; just as adding modes of action with ag chemicals improves herbicide control rates, the wrong mix of chemicals can also create antagonism and cause a disaster. The same can be seen when tank mixing soil health products. This antagonism may not express itself as you may see in pesticide tank mix but could be just as devasting to your crop or act in a way to impede the mode of action of the products you mixed. Understanding a soil health product’s mode of action and how it interacts with other products are critical components to achieving tank mix or “blend” success.
Start with a Solution in Mind
Before you can get started blending soil health products, you must decide what you want to utilize in your operation, which can be a daunting step in this process due to the confusion in the marketplace. Thus, the first question to ask is what are you trying to achieve? You need to start with an end goal in mind. I would suggest you evaluate what is the yield limiting factor in your field. For example, is soil compaction leading to poor soil drainage and water holding capacity issues? Is your soil sample showing adequate nutrient levels, but nutrients aren’t seeming to move into the plants? Are nutrients not staying in your soils and leaching away? You may find that you have more than one issue. Once you can identify the main issue/s you are having in your field you can begin to select the correct mode of action/s to address the problems. Table 2 will walk you through a few common scenarios that are encountered in many fields that would benefit from soil health products and examples of products that would be a solution to those problems.
Table 2
Building Your Soil Health Blend for Success
Now that we understand mode of action solution-based approaches, we can now begin to build a soil health blend. The next step are things to consider such as incompatibilities or antagonisms between products or in the field. Just like pesticide tank mixes physical, biological and chemical incompatibilities can occur with soil health products. Table 3, is a soil health blend checklist of questions you should ask while evaluating and building your soil health blend. The questions outlined in Table 3, not only encompass the mixing of the products but also bring to light other considerations such as shelf-life, viability and storage and handling requirements that may be different from other inputs we are more commonly used to.
Table 3
Soil health blends are the future of unlocking higher yields, more effective nutrient use, and improved crop quality. Understanding product mode of action and seeking sound advice from your retailer, CCA, or trusted advisor is key. To continue to improve our outputs we must be focused on our inputs. I challenge all of you to start thinking on how soil health blends can be utilized as a tool for success. If we think in terms of nutrient inputs, we would never consider only applying one standalone nutrient to a crop, and the same holds true for adding soil health inputs. Diversifying our inputs based on product mode of action, environmental needs and adopting the principal of blending soil health products will increase our chances of success in the field.
Table 4
Resources
Tank mixing guide: https://ag.purdue.edu/department/extension/ppp/ppp-publications/ppp-122.pdf-
Research on combining biostumulants: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6243119/
Figure 1. Microbial shift following decline of citrus trees caused by Huanglongbing (Ginnan et al. 2020).
The world population is projected to reach about 10 billion individuals by 2050. As a result, the agricultural sector needs to produce more food despite several looming challenges, including the shrinking of arable land, erratic and extreme weather patterns and pest and disease outbreaks. Higher agricultural outputs per surface basis is one key element to solve the equation of a growing demand, which inevitably results in an increase of agrochemical inputs (pesticides, fertilizers). The global agrochemical market size is valued at $235.2 billion in 2023 and is expected to reach $280 billion by 2028, growing at a compound annual growth rate (CAGR) of 3.7% during the forecast period. The major driving force behind this uptrend comes from the organic sector. Hence, the global agricultural biologicals market (biopesticides, biostimulants and biofertilizers) is projected t
grow at a CAGR of 13.8% to reach $27.9 billion by 2029 from $14.6 billion in 2023.
There is a growing consumer demand for organically grown and safe agricultural products. There is also a collective awareness of the potential risks associated with pesticide use, including impact on human health (e.g., increase of cancers linked to pesticide use), contamination of environmental resources (e.g., leaching of chemicals in groundwater) and non-target side effects on wildlife (e.g., bee population collapse). This has led to a tightening of policies by governments and regulatory agencies for conventional chemical use and chemical residue limits and the phasing out of harsh synthetic agrochemicals. Growers are at the forefront of the sustainable ag movement and have adapted their farming practices to meet both consumer and agency demands. Replacing synthetic chemicals with organic products or biologicals in their agrochemical arsenal can be challenging because of the limited scientific information on their mode of action and range of efficacy. In this article, we will mostly focus the discussion on sustainable strategies to control diseases with biopesticides, the discovery pipeline within the framework of my research and the prospects for the future.
In Integrated Pest Management
Fostering sustainable farming practices that promote and enhance agroecosystem health and increase biodiversity are instrumental to our long-term success. Integrated pest and disease management programs (IPM or IPDM) have been central to this philosophy. The framework of IPM programs is to reduce synthetic agrochemical inputs and rely first on alternative strategies, such as adapted management practices, use of resistant/tolerant plant varieties and deployment of organic agrochemicals and biologicals. IPM programs were at times challenging to implement to manage certain crop diseases because of the lack of relevant alternatives to synthetic agrochemicals. Organic agrochemicals suffer from a short window of activity and under high disease pressure they must be applied often. Also, those products are not free of environmental risks. For example, the copper-based Bordeaux mixtures have been used for over a century in viticulture and are known to impoverish vineyard soil biota and affect aromas in wine.
Biologicals also often suffered from a lack of credibility because of their inconsistency to control diseases. From a grower standpoint, there is too much economical risk to rely on uncertainty. However, recent scientific discoveries and technological advances have helped strengthen IPM programs in many ways. First, they have and continue to improve the formulations of agrochemicals (conventional, organic and biological) and, most importantly, their deliveries to target pests and pathogens. Scientific reports indicated that only 0.1% to 1% of sprayed material reaches its target depending on the system. Thus, increasing delivery efficiency will reduce leaching of chemicals in the environment. Second, the advent of ‘omics’ technologies and affordability of sequencing costs have allowed industry to identify biological candidates in a quick and reliable manner. This has revolutionized the field of microbiology (among others) that traditionally used ancestral culturing techniques to single out biological agents from environmental samples, which equated to finding a needle in a haystack. In today’s era, we can generate large-sequence datasets that capture not only entire microbial communities associated with plants or environments but also shed light on their biological functions. To be able to see in a high-throughput manner ‘who does what’ has streamlined the discovery of biological products.
Finding Beneficial Microbes for Diseased Systems
My lab has been using omics tools to identify beneficial organisms inhabiting citrus and grapevine that could be leveraged to manage Huanglongbing (HLB) and Pierce’s disease (PD), respectively. Both diseases are caused by bacterial pathogens transmitted by insect vectors following feeding on the plant host. In citrus HLB, the bacterium (Candidatus Liberibacter asiaticus) lives in the phloem tissues that transport sugars downwards, from leaves to fruits and roots. In grapevine, the bacterium (Xylella fastidiosa) lives in the xylem tissues that transport water and nutrients upwards from roots to leaves. In both pathosystems, the buildup of bacteria in the hosts’ vasculature leads to disruption of channel transport to a point that becomes detrimental to the plant. Citrus and grapevine decline can happen in as quickly as two years, but in some cases, the hosts can sustain the infection for several years. Our hypothesis is the microbial communities living with the host provide protection against the pathogens with the goal of leveraging their benefits for crop protection.
Figure 1. Microbial shift following decline of citrus trees caused by Huanglongbing (Ginnan et al. 2020).
A survey of citrus orchards in Florida and sequencing of the microbial communities associated with roots of trees with a range of disease symptoms revealed interesting information on the disease etiology (Figure 1). Our results showed there was an initial decline of keystone taxa (native organisms that play a role in the stability of an ecosystem) and symbionts such as mycorrhizae fungi for trees that contracted the disease (Phase I). This was followed by a microbe-mediated response to infection, with enrichment of several beneficial organisms that have the capabilities to stimulate the tree immune response or provide direct antibiosis to pathogens (Phase II). In the late phase of the infection (Phase III), we measured an increase of soilborne parasites and pathogens (Fusarium, Phytophthora) and saprophytic fungi that decompose decayed roots. Those findings indicate either HLB made trees more vulnerable to root pathogens or vice versa, but in either case, this synergistic effect caused trees to decline at a faster pace. This research led to the pursuit of two strategies that are now being evaluated to combat HLB. The first strategy is to re-introduce into the system beneficial microbes or microbial natural products isolated from Phase II and verify these can support tree immunity. The second strategy is to identify cultural practices like soil amendments that support the keystone and symbiotic communities.
Similar to citrus, we surveyed vineyards and profiled the microbiome of grapevine with a range of Pierce’s disease symptoms (Figure 2). Here, we found interesting data when looking at the vine lignified shoot tissues (canes). In comparison to the root system, there are very few microbes living in the plant vasculature and even more so in annual tissues like canes that are pruned off every year. This is a perfect environment for the pathogenic bacterium to thrive due to the limited microbial competition. Our results showed that, just like in citrus roots, there was a microbial-mediated response to infection and that two bacteria that also inhabit the vascular system correlated negatively with the pathogen Xylella fastidiosa. In other words, when those two beneficial bacteria were present and abundant, the pathogenic bacterium was low, and vines were healthy. Our group further re-isolated those beneficial bacteria and confirmed in greenhouse bioassays that when they were inoculated to grapevine, they provided protection against Pierce’s disease. These biological control agents are currently being evaluated at UC Davis in field trials. UC patented those technologies, and we are partnering with the private sector to develop injectable or sprayable products that could be commercialized for Pierce’s disease management.
Figure 2. Microbial mediated response to grapevine Pierce’s disease (PD) infection. A) Mild PD infection; B) intermediate PD infection; and C) severe PD infection. Bottom panel shows the bacterial response to infection in intermediate PD infection (Deyett and Rolshausen 2019).
There is a push from agricultural commodities to replace synthetic agrochemicals with environmentally friendly solutions. There are a lot of incentives for agrochemical companies to develop bio-based products, including an easier path to EPA registration. The lower residual toxicity levels of biopesticides make them the perfect choice to meet stringent environmental standards and address food safety and quality. However, biologicals still suffer from higher production costs because they are not produced and distributed in high volumes like their synthetic chemical counterparts. Increasing scalability and improving consistency in efficacy are two major hurdles for biopesticides to gain larger market share in the future.
References
Ginnan et al. 2020. Phytobiomes. https://doi.org/10.1094/PBIOMES-04-20-0027-R
Deyett and Rolshausen 2019. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2019.01246
Understanding vine nutrient status and determining their nutrient needs are as important as fertilization itself (all photos by T. Tian.)
Proper nutrition management allows vines to grow healthy canopies and produce fruit with desirable quality. Fertilization is used to correct nutrient deficiency and improve vine productivity. Even in vines without foliar symptoms, growers may fertilize as a routine practice to compensate nutrient loss at harvest and prevent nutrient deficiency. As a result, sometimes managing vine nutrition simply means applying fertilizers. I would argue that understanding vine nutrient status and determining their nutrient needs are as important as fertilization itself.
Grapevines have lower fertilization requirements than many agricultural crops.
Overfertilization does not offer many benefits from economic or vine productivity points of view. Instead, it could compromise vine balance, decrease fruit quality and negatively affect the environment. Let’s use nitrogen (N) as an example here. Excessive N additions lead to jungle-like canopy with limited light penetration and air circulation, increase disease pressure and negatively affect fruit quality. Excessive amounts of nitrate in the soil also increase the risk of groundwater and surface water contamination.
Supplying vines with ample but not excessive nutrients is easier said than done. In this article, I will start the story with summarizing previous work on whole vine nutrient budget and then extend the discussion to determining vine nutrient requirements and fertilization.
In terms of macronutrients, annual growth is a strong sink for nitrogen, phosphorus, potassium, calcium and magnesium between bud break and veraison.
Whole Vine Nutrient Budget
Studies were conducted under field conditions in California and Oregon and in potted systems in South Africa to track nutrient uptake, movement and distribution among vine organs at different phenological stages.
In terms of macronutrients, annual growth is a strong sink for N, phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) between bud break and veraison. Required nutrients of shoots, leaves and clusters can be obtained from two pools: nutrients remobilized from permanent organs and those taken from soil. In mature vines, up to 50% of N and P in new growth can be supplied by the stored reserve in trunks and roots. On the other hand, less than 15% of K, Ca and Mg are remobilized from the reserve, since only a small percentage of those nutrients can be recycled during leaf fall. Clearly, nutrients obtained from the soil still account for a large portion of required nutrients, even in the mature vines. Young vines have less nutrient reserve than older vines, and thus rely more on nutrients supplied by root systems. Nitrogen uptake peaks between bud break and bloom, while uptake of other macronutrients usually reach the max between bloom and veraison. Nutrient uptake also takes place after harvest when nutrients are available in the soil and weather conditions are favorable.
Even if the tissue nutrient concentration of a vineyard is slightly below the given normal range, it does not mean vines surely experience nutrient deficiency.
The uptake and distribution of micronutrients is less understood as compared to macronutrients. Dr. Paul Schreiner, scientist at USDA-ARS, studies the budget of micronutrient in young and older ‘Pinot noir’ vines in Oregon’s Willamette Valley. In young vines, boron, zinc, manganese and copper were taken between bud break and harvest, with the peak of uptake occurring between bloom and veraison. The uptake and allocation of micronutrients appears less consistent in mature vines.
Please note that research findings reflect vine nutrient budget under specific conditions and should be interpreted with caution. Factors like soil nutrient availability, irrigation practices, rootstock and scion combination and weather conditions have large impacts on nutrient uptake and allocation. Clearly, vine nutrient demand varies between vineyards. So, how should one determine whether fertilization is needed at a specific site?
Determine Nutrient Requirement of Vines
Nutrient analyses of leaf blades and leaf petioles at bloom and veraison are indicators of vine nutrient status. Many testing labs provide the comparison of leaf nutrient concentration to the normal range for each nutrient.
We recommend growers not relying solely on numbers on lab results to make fertilization decisions. First, variability in vine nutrient requirement is expected between vineyards and across seasons. Even if the tissue nutrient concentration of a vineyard is slightly below the given normal range, it does not mean vines surely experience nutrient deficiency. Second, normal ranges of leaf nutrients are estimated in experiments where vines received a specific nutrient at different rates and had its concentration over a wide range of leaf tissues. Given the difference in experimental setup, the normal range determined can vary between studies. Thus, the normal range for nutrients should be used only as references when it comes to interpreting vine nutrient requirements. Historical nutrient data, vine growth and production goals are important to consider. For example, fast-growing canopies may have lower leaf N concentration, especially in newly expanded leaves, but does not mean that vines require N fertilization. Instead, rapid shoot growth often indicates ample N and water availability in the soil.
Fertilization
In vineyards where fertilization is needed, growers and CCAs often ask me about the amount, formula and application timing of fertilizer. Rather than providing generalized answers for those questions, I would like to share some tips. Please feel free to reach out for questions related to your vineyards.
About 3 lb N, 0.5 lb P and 5 lb K are removed from a vineyard with each ton of harvested fruit. Many would use those numbers to calculate how much fertilizer is needed to compensate the loss during harvest. In reality, supplementing vines only with nutrients removed from the vineyard may not be sufficient. For instance, data from western Oregon showed that young ‘Pinot noir’ vines acquired 12.5 lb N, 3 lb P and 25 lb K per acre via uptake with the crop level at 2.0 ton/acre.
Compost is an affordable, slow-releasing fertilizer. Applying compost in the spring supplements vines with nutrients, boost soil microbial activity, improves soil water penetration by aggregation and enhances water holding capacity. Increasing soil organic matter is good practice for soil health in general.
Soil pH plays key roles on nutrient availability. Most nutrients become more available in soils with neutral pH. Regular soil sampling and testing can help with managing and adjusting soil pH if needed.
If nutrient deficiency is observed late in the season, immediate fertilization may not alleviate the symptoms. It is because the period when nutrient deficiency becomes evident would not be coincident with the period when nutrient uptake peaks. Making applications at the right timing in the following season may be more effective on correcting deficiency.
Even though vines obtain nutrients mainly from the soil by roots, foliar application can be an additional tool to supplement vines with nutrients. In the past, we successfully increased fruit N at harvest in wine grapes by applying urea to foliage between fruit set and veraison. Foliar application of P and Mg was found to reduce leaf symptoms in wine grapes. Some PCAs suggest foliar Ca and Mg sprays between bloom and veraison can increase berry firmness and reduce powdery mildew occurrence in table grapes.
Applying fertilizers in small doses may improve fertilization efficiency in vineyards with shallow root systems. Theoretically, frequent fertilization with lower doses allows roots to better catch nutrients and reduce leaching.
References
Araujo FJ and Williams LE. 1988. Dry matter and nitrogen partitioning and root growth of young field-grown Thompson Seedless grapevines. Vitis 27:21-32.
Conradie WJ. 1980. Seasonal uptake of nutrients by Chenin blanc in sand culture: I. Nitrogen. S Afr J Enol Vitic 1:59-65.
Conradie WJ. 1981. Seasonal uptake of nutrients by Chenin blanc in sand culture: II. Phosphorus, potassium, calcium and magnesium. S Afr J Enol Vitic 2:7-14.
Schreiner RP, Scagel CF and Baham J. 2006. Nutrient uptake and distribution in a mature ‘Pinot noir’ vineyard. HortScience 41:336-345
Schreiner RP. 2016. Nutrient uptake and distribution in young Pinot noir grapevines over two seasons. Am J Enol Vitic 67:436-448
