Improvements in irrigation water productivity constitute an ongoing effort globally. In California, growers are under regulatory pressure to stabilize groundwater levels and reduce nitrate leaching, partially, by further improvements in irrigation optimization. Evapotranspiration (ET)-based methods can inform crop water requirements and boost irrigation efficiency, but in practice, they can be challenging for farmers to implement, especially in vegetable systems. Irrigation field trials were conducted near Salinas CA in 2018 and 2019 to evaluate the crop coefficient model employed by the CropManage ET-based irrigation decision support system (DSS) for summer cauliflower (Brassica oleracea var. botrytis cv. Symphony) and investigate potential water savings through improved irrigation scheduling. Overhead sprinklers were used for crop establishment, and surface drip was used subsequently. A randomized complete block design was used to administer treatments near 50, 75, 100, and 150% of crop evapotranspiration (ET) during the drip period with an added treatment at 125% in 2019. Water requirement for the 100% treatment was determined by the CropManage DSS model based on crop coefficients derived from fractional canopy cover. Deliveries to remaining treatments were scaled proportionally. The total yield and irrigation productivity were maximized by the 100% treatment both years with total applied water ranging from 275 to 300 mm. At present, the reported water application for summer cauliflower averages 465 mm in the region. Hence, implementing ET-based irrigation scheduling, administered through the CropManage DSS, could reduce water use in summer cauliflower by an average of 30% relative to current practices and serve to enhance groundwater management while maintaining crop returns.

Subsurface drip irrigation (SDI) is defined as a low-pressure, high-efficiency irrigation system that uses drip tubes or drip tape with microirrigation emitters and is installed below the soil surface to apply water to meet crop water requirements. When compared with other irrigation systems, SDI has advantages and disadvantages that should be carefully considered. There are many design and management aspects that are similar to surface drip irrigation (DI), but there are also some unique differences that can potentially affect water application uniformity, operation, and system longevity. SDI can potentially provide a more consistent soil water and nutrient environment for optimizing crop growth and production than other irrigation methods, but it can also present some challenges depending on the climate, soil type, and crop, such as plant establishment, salinity management, soil water redistribution, and the application of agrochemicals. This chapter provides background for making decisions on the design, maintenance, and operation of SDI systems and reviews research on adapting SDI to a range of crops and field conditions. With attention to design and proper management and maintenance, SDI can often improve water and nutrient use efficiency and, in many instances, crop yield responses.

Vegetable growers on the central coast of California are under regulatory pressure to reduce nitrate loading to ground and surface water supplies. California also implemented legislation that limits agricultural pumping in regions such as the central coast where the aquifers have been over-extracted for crop irrigation. Growers could potentially use less N fertilizer, address water quality concerns, and conserve water by improving water management and matching nitrogen applications to the N uptake pattern of their crops. Two tools available to growers, the soil nitrate quick test (SNQT) and reference evapotranspiration (ETo) data have been previously shown to improve the management of water and fertilizer nitrogen in vegetable production systems. However, adoption of these practices has not been widespread. These techniques can be time consuming to use, and vegetable growers often have many crops to manage. To address such time constraints, the CropManage online application (cropmanage.ucanr.edu) was developed to facilitate implementation of the SNQT and evapotranspiration-based irrigation scheduling. CropManage additionally helps growers account for plant available N from background levels of nitrate in irrigation water. Trials were conducted in commercial vegetable fields in the Salinas Valley during 2012–2019 to evaluate CropManage fertilizer and irrigation recommendations relative to the grower practice. Results demonstrated that in many cases fertilizer or irrigation reductions could be attained by following CropManage recommendations without jeopardizing yield. In lettuce, the total fertilizer N applied under CropManage guidance was reduced by an average of 31 % compared to the grower standard practice. Lettuce yield within the CropManage treatment averaged 107 % of the grower practice. CropManage guidance in broccoli reduced N and applied water by 24 % and 27 %, respectively, compared to the grower standard practice, while average yield was similar between treatments. Management tools such as CropManage can support operational efficiencies and compliance with regulatory targets designed to improve groundwater quality.

Organic cool-season vegetable growers on the Central Coast face challenges in applying nitrogen (N) to balance yields with new environmental regulations. It is hard to time fertilizer applications while calculating N mineralization of soil organic matter and organic fertilizers to plant-available N. Organic fertilizers with high phosphorus (P) to N ratios may elevate P levels and harm surface water quality. In this study, we evaluated (1) mineralization of soil organic matter and fertilizers, (2) effectiveness of residual soil nitrate-N tests and (3) long-term impacts of organic fertilizers on P levels and soil microbial activity. We found that mineralization of N from soil organic matter provided limited N to leafy green vegetables. Soil tests were more reliable in heavier than sandier soils. Application rates of 4-4-2 were calculated to meet N demands, resulting in an oversupply of P. However, only 9% to 17% of fertilizer P solubilized without elevating available soil P levels. While it's difficult for organic vegetable growers to use cover crops, organic fertilizers increased carbon levels, resulting in higher levels of soil microbial activity.

Cool season vegetables require adequate soil moisture to assure that maximum yield and quality are achieved. On California’s central coast, where the majority of cool season vegetables are produced in the US, long-term overpumping of irrigation water has reduced groundwater levels and led to environmental degradation. Two evapotranspiration (ET) based irrigation field trials were performed near Salinas CA (USA) to determine if ET-based irrigation scheduling could conserve water while producing romaine lettuce (cv. Sun Valley) of commercially viable yield. Sprinklers were used for seed germination and crop establishment. Four drip irrigation treatments were then imposed using a randomized complete block design with six replications. The CropManage decision-support model was used to estimate the full (100%) crop water requirement based mainly on ET replacement. Other treatments included 50% 75% and 150% of the full water requirement. The 100% treatment received 185 mm of water in 2015 and 247 mm in 2016, both of which were well below prior guidance and grower reports. Yields from the 100% and 150% treatments were not significantly different and were similar to industry average, while yields were significantly lower for the 50% and 75% treatments. The 100% treatment had the highest water use efficiency, and the 100% and 150% treatments together had the highest nitrogen recovery efficiency. Irrigation of romaine near the 100% ET replacement level can potentially reduce environmental impacts associated with nitrate leaching and surface runoff.

Neonicotinoid insecticide use has increased over the last decade, including as agricultural seed treatments (application of chemical in a coating to the seed prior to planting). In California, multiple crops, including lettuce, can be grown using neonicotinoid treated seeds or receive a direct neonicotinoid soil application (drenching) at planting. Using research plots, this study compared pesticide runoff in four treatments: (1) imi-dacloprid seed treatment; (2) clothianidin seed treatment; (3) imidacloprid drench and an azoxystrobin seed treatment; and (4) a control with no pesticidal treatment. Neonicotinoid and azoxystrobin concentrations were measured in surface water runoff during six irrigations events in the 2020 growing seasons. Results showed runoff concentrations up to 1308 (& PLUSMN;1200) ng L-1 for imidacloprid drench treatment, 431 (& PLUSMN;100) ng L-1 for clothianidin seed treatment, 135 (& PLUSMN;60) ng L-1 for imidacloprid seed treatment, and 13 (& PLUSMN;10) ng L-1 for azoxystrobin seed treatment (treatments averaged). The percent of applied mass in runoff over the entire sam-pling period varied by compound; the imidacloprid seed treatment and drench were similar (0.015 and 0.019%, respectively) to the clothianidin seed treatment (0.036%) while the azoxystrobin seed treatment was much higher (15%). Although the proportion of imidacloprid in runoff was similar for imidacloprid treatments, the mass applied during soil drench was > 4x the amount applied from the imidacloprid seed treatment. Surface soils were collected before planting and at the end of the trial. The neonicotinoids were detected in soil throughout the study and average maximum concentrations were 9-13 ng g-1; azoxystrobin was detected in only two soils at concentrations up to 0.57 ng g-1. These results elucidate the comparative mass runoff resulting from planting treated seed and soil drench applications and highlight the value of additional work to characterize off-site transport from the many commodities that may be utilizing treated seeds.

Pyrethroid and neonicotinoid pesticides control an array of insect pests in leafy greens, but there are concerns about the off-site movement and potential water quality impacts of these chemicals. Effective on-farm management practices can eliminate aquatic toxicity and pesticides in runoff. This project evaluated an integrated vegetated treatment system (VTS), including the use of polyacrylamide (PAM), for minimizing the toxicity of imidacloprid and permethrin pesticides in runoff. The VTS incorporated a sediment trap to remove coarse particles, a grass-lined ditch with compost swales to remove suspended sediment and insecticides, and granulated activated carbon (GAC) or biochar to remove residual insecticides. Runoff was sampled throughout the VTS and analyzed for pesticide concentrations, and aquatic toxicity using the midge Chironomus dilutus and the amphipod Hyalella azteca. In simulated runoff experiments, the VTS reduced suspended sediment load by 88%, and imidacloprid and permethrin load by 97% and 99%, respectively. In runoff events from a conventionally grown lettuce field, suspended sediment load was reduced by 98%, and insecticide load by 99%. Toxicity was significantly reduced in approximately half of the simulated runoff events, and most of the lettuce runoff events. Integrated vegetated treatment systems that include components for treating soluble and hydrophobic pesticides are vital tools for reducing pesticide load and occurrence of pesticide-related toxicity.

Nitrogen (N) and irrigation water must be effectively used in mineral soils to produce carrots with high yield and minimal environmental impact. This study attempts to identify optimal N and irrigation management practices for low desert carrot production in California by investigating consumptive water use and N uptake and removal rates in fresh market and processing carrots. Field experiments were conducted at the University of California Desert Research and Extension Center and nine farmer fields during two growing seasons. The actual evapotranspiration (ETa) was measured using the residual energy balance method with a combination of surface renewal and eddy covariance equipment. Crop canopy coverage, actual soil nitrate-N from multiple depths as well as total N percentage, dry matter, and fresh biomass in roots and tops were measured over the growing seasons. The length of the crop season had a wide range amongst the experimental sites: from a 128-day period in a processing carrot field to as long as 193 days in a fresh market carrot field. The seasonal ETa varied between 305.8 mm at a silty loam furrow irrigated processing carrot field and 486.2 mm at a sandy clay loam sprinkler irrigated fresh market field. The total N accumulated at harvest ranged between 205.4 kg ha−1 (nearly 52% in roots) and 350.5 kg ha−1 (nearly 64% in roots). While the mean value of nitrogen removed by carrot roots varied from 1.24 to 1.73 kg N/Mg carrot roots, it appears that more N was applied than was removed by carrot roots at all sites. Within the range of N application rates examined at the experimental sites, there was no significant relationship between carrot fresh root yield and N application rate, although the results suggested a positive effect of N application on carrot yield. Sufficient soil N availability over the growing season and the lack of significant yield response to N application illuminated that optimal N rates are likely less than the total amounts of N applied at most sites.

The impact of plant development, environmental conditions at the time of inoculation, and inoculum concentration on survival of attenuated BSL1 Escherichia coli O157:H7 strain ATCC 700728 on field-grown romaine lettuce was evaluated over 3 years. E. coli 700728 was inoculated onto 4- and 6-week-old romaine lettuce plants in the Salinas Valley, CA, at night or the next morning with either low (5 log) or high (7 log) cell numbers per plant to simulate a single aqueous contamination event. At night, when leaf wetness and humidity levels were high, E. coli cell numbers declined by 0.5 log CFU/plant over the first 8-10 h. When applied in the morning, E. coli populations declined up to 2 log CFU/plant within 2 h. However, similar numbers of E. coli were retrieved from lettuce plants at 2 and 7 days. E. coli cell numbers per plant were significantly lower (P < 0.05) 7 days after application onto 4-week-old compared to 6-week-old plants. E. coli 700728 could be recovered by plating or enrichment from a greater proportion of plants for longer times when inoculated at high compared with low initial concentrations and after inoculation of 6-week-old plants compared with 4-week-old plants, even at the low initial inoculum. A contamination event near harvest or when leaf wetness and humidity levels are high may enhance survivability, even when low numbers of E. coli are introduced.

Robustness is the measure of the ability to perform well across multiple environments. The genetics of robustness in lettuce (Lactuca sativa L.) under changing nitrogen (N) application was studied by two parameters obtained from linear regression analysis. Robustness in changing water application was assessed by two parameters: relative efficiency component (REC) and susceptibility component (SC). The efficiency, sensitivity, and the effect of reduced irrigation on these parameters was assessed for 50 lines of lettuce in 2011. Efficiency, sensitivity, and plant N uptake and utilization were important traits in robustness under changing N application. Eight cultivars were re-evaluated in 2012, 2014, and 2016 under high- and low-N treatments in order to estimate the repeatability of efficiency and sensitivity. Repeatability was greater for efficiency than sensitivity. In addition, the genetics of efficiency, sensitivity, REC, SC, nutrient concentration, nutrient content, dry-to-fresh biomass percentage, bolting, and shoot biomass production were studied by quantitative trait locus (QTL) analysis of a recombinant inbred line (RIL) population derived from the cultivars Grand Rapids and Iceberg. The population was phenotyped in three experiments and genotyped by sequencing. Major clusters of QTL for these traits were identified in linkage groups (LGs) 3, 7, and 9. Minor-effect QTL for sensitivity were identified in LGs 3 and 4. Intermediate-effect QTL for SC were identified in LGs 4 and 7. These results provide evidence that the components of robustness under changing N (efficiency and sensitivity) and water (REC and SC) availability are genetically independent and can be improved through breeding.

The main objective of this study was to explore the viability of drip irrigation for organic spinach production and the management of spinach downy mildew disease in California. The experiment was conducted over two crop seasons at the University of California Desert Research and Extension Center located in the low desert of California. Various combinations of dripline spacings and installation depths were assessed and compared with sprinkler irrigation as control treatment. Comprehensive data collection was carried out to fully understand the differences between the irrigation treatments. Statistical analysis indicated very strong evidence for an overall effect of the irrigation system on spinach fresh yields, while the number of driplines in bed had a significant impact on the shoot biomass yield. The developed canopy crop curves revealed that the leaf density of drip irrigation treatments was slightly behind (1–4 days, depending on the irrigation treatment and crop season) that of the sprinkler irrigation treatment in time. The results also demonstrated an overall effect of irrigation treatment on downy mildew, in which downy mildew incidence was lower in plots irrigated by drips following emergence when compared to the sprinkler. The study concluded that drip irrigation has the potential to be used to produce organic spinach, conserve water, enhance the efficiency of water use, and manage downy mildew, but further work is required to optimize system design, irrigation, and nitrogen management practices, as well as strategies to maintain productivity and economic viability of utilizing drip irrigation for spinach.

D roughts are a frequent phenomenon of the Californian climate, recurring every 5 to 15 years and lasting for 1 to 4 years.Because most of the developed water in California is needed for growing crops, droughts have far-reaching consequences for the agricultural industry.As the state population continues to grow and more water is needed for sustaining wildlife habitat, less irrigation water may be available for farmers than in the past.Contingency for drought should be part of every grower's business plan in California.This publication outlines a range of strategies to consider for growing vegetables under a limited water supply. Evaluate Options for Maximizing Production and ProfitabilityWhen water supplies are limited during a drought, options to maximize production and profitability need to be considered.Producing crops that are most profitable per unit of applied water is an important consideration, as well as growing crops during periods when prices are higher than normal.Because yield and quality of vegetable crops usually decline when underirrigated, it is often better to reduce the acres planted than to spread a limited water supply over too large of an area.For some warm season vegetables such as tomatoes and some melons, water stress may increase brix and other flavor qualities if timed during fruit maturation and ripening, but yield may also decline.UC ANR Drought Tip 8632 covers how to estimate vegetable crop water needs and the acres that can be irrigated when water supplies are limited (Cahn 2019).If it is necessary to reduce planted acreage due to a limited water supply, then consider planting on the most productive land.This should be land with soils most suited for vegetable production, such as uniform, deep soils or land in the best climatic zone.Avoid land with soils that have high salinity, impermeable and compacted layers, or excessive slope.

Over the last 20 years, subsurface drip irrigation has been widely adopted for processing tomato (Solarium lycopersicum L.) production in California. Subsurface drip irrigation allows application of water and nitrogen (N) fertilizer throughout the season. As a result, optimal N fertilization approaches are likely different than for furrow-irrigated systems. A project was initiated to develop and validate an N fertilization budget with site specific input for drip-irrigated processing tomatoes. Nitrogen partitioning in the aboveground biomass was determined in ten commercial fields. At harvest, the N concentration in the fruit averaged 1.5 g N kg(-1), which accounted for 64% of the total N in the aboveground biomass. A budget, which considered residual soil mineral N, nitrate in the irrigation water and N mineralized from soil organic matter, was implemented in a replicated field trial with three application rates ranging from 152 to 306 kg ha(-1). Average yields reached 130 and 140 Mg ha(-1) in 2017 and 2018, respectively. Nitrogen application rates had no significant effect on yield. However, across both years the total N in the aboveground biomass increased significantly by 0.875 kg kg(-1) of additional N. Nitrogen mineralization of residues incorporated after the tomato harvest was slow during the winter, with soil nitrate levels in the top 60 cm of the profile not being different from soil where the residues had been removed after the tomato harvest.