Project : USDA ARS

ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Water Management Research » Research » Research Project #441662

Research Project: Improving Soil and Water Productivity and Quality in Irrigated Cropping Systems

Location: Water Management Research

2024 Annual Report

Objectives
The San Joaquin Valley of California is one of the richest agricultural regions in the world. Crop production in this region relies on irrigation water, which is increasingly jeopardized by a substantial water crisis. This multidisciplinary project includes three main goals. Our first goal is to develop agricultural management strategies that enhance soil quality and water productivity. Secondly, our work will help optimize the efficiency of irrigation practices. Finally, this work helps maximize the potential for using low-quality water. Specifically, we will evaluate the impacts of soil conservation practices, cover crops, and whole orchard recycling in cropping systems dominant in the San Joaquin Valley. These strategies impact soil’s capacity to store and filter water. Next, through on-farm experimentation and remote-sensing modeling, we will identify ways to enhance irrigation efficiency. To achieve this, we will determine seasonal crop water demands, optimize irrigation timing and amounts, and evaluate if lower irrigation inputs impact nectarine, pomegranate, and citrus yield and quality. Further, salt, selenium (Se), and boron (B) laden drainage and groundwater sources will be considered for irrigation of many cropping systems. Salt and B tolerant crops utilize such poor-quality waters, manage trace elements residing in the soil from the use of these waters, and can serve as Se-enriched products of economic and nutritional value. Altogether, this systems-level approach thoroughly evaluates many tools that California growers and producers can use to manage their farms under increasing water limitations. This research is urgent and addresses the critical needs of growers and commodity boards. Moreover, these data can be used to address the goals of government and non-profit organizations to enhance agricultural sustainability within the decade. Objective 1: Identify benefits of conservation practices (cover crop, crop diversification, whole orchard recycling, organic soil amendment) for irrigated agriculture. • Sub-objective 1.A: Evaluate the capacity of conservation practices to enhance irrigation water productivity. • Sub-objective 1.B: Determine greenhouse gas emissions, understand N dynamics, and develop N management strategies in almonds orchards after WOR. • Sub-objective 1.C: Investigate interactive effects of organic and inorganic N fertilization and soil building conservation practices for improving soil and water quality in California almond orchards. Objective 2: Develop deficit irrigation strategies for perennial fruiting crops. • Sub-objective 2.A: Determine water requirement and deficit irrigation strategies in early-season nectarine. • Sub-objective 2.B: Develop deficit irrigation strategies for optimized water productivity in pomegranate. • Sub-objective 2.C: Determine watershed-scale crop water use and water savings using simulated deficit irrigation in commercially grown citrus. Objective 3: Develop sustainable agricultural water reuse systems with alternative crops to protect soil/environmental health of drainage impacted soils when using poor-quality water.

Approach
Sub-objective 1A: We aim to reveal impacts of cover crops on soil water holding capacity, soil biological diversity, berry yield and quality, and weed pressure in a table grape vineyard. Soil and vines will be analyzed to quantify soil microbial biomass and community compositions, soil carbon (C) and nutrients, and crop yield, quality, and water productivity. If cover crops fail to re-establish, we will re-seed. Sub-objective 1B: We aim to quantify GHG emissions, woodchip mineralization, and nutrient availability in orchard soils after whole orchard recycling (WOR). Using field plots, soil GHG emissions, nitrate leaching potential, and nitrogen (N) transformation and movement will be quantified. Lab experiments will evaluate impacts of woodchip sizes and soil moisture on similar soil properties. If field operations interfere with sampling, we will sample the field, once accessible. Sub-objective 1C: We aim to reveal impacts of compost with conservation practices on soil biological properties. Soil microcosms developed from WOR and cover crop almond orchards will be amended with compost or inorganic N fertilizer and evaluated for soil microbial properties, C, N, and nitrate. Grower selection of cover crop species will not impact the project. Sub-objective 2A: We hypothesize that postharvest deficit irrigation (DI) reduces consumptive water use in early-season nectarine without affecting fruit yield and quality. DI strategies will be applied to nectarine research plots and tree health and fruit yield and quality metrics will be determined. If the pre-selected DI rates are too high or too low, they will be adjusted. Sub-objective 2B: We hypothesize that regulated DI increases water use efficiency, water productivity, and economic returns in pomegranate. Field and laboratory measurements will evaluate effects of DI on soil water availability, pomegranate tree growth characteristics, fruit yield and quality, and water productivity. If lysimeters, used to guide irrigation scheduling fail, then water content and weather data will be used. Sub-objective 2C: We aim to determine consumptive water use in evapotranspiration (ET) of citrus crops under grower practice and simulated DI. At two citrus orchards, eddy-covariance towers with sensors will be used to calculate standardized reference ET, which will be compared to corresponding satellite pixel estimates and to local ground-based estimates. If data is not available from growers, we will use the field, remote sensing, and published data. Objective 3: We aim to develop agronomic systems tolerant to poor-quality water that can manage soil selenium; determine drainage water impacts on salt-tolerant crops in crop rotation; and reveal the effects of long-term saline irrigation in pistachio. Guayule, agretti, and pistachio crop yield, quality, and salt accumulation will be evaluated in field trials with poor-quality irrigation water. If cooperator field plots are no longer available, alternative sites will be used.

Progress Report
This report documents progress for project 2034-13000-013-000D, titled, “Improving Soil and Water Productivity and Quality in Irrigated Cropping Systems”, which started in January 2022. Under Sub-objective 1A, cool-season cover crop treatments were maintained in a table grape vineyard, including Tansy Phacelia or ‘Merced’ cereal rye cover crops, and a control with interrow spaces maintained bare using herbicide for weed control. The percent cover of the cover crop treatment or weeds were quantified demonstrating successful cover crop establishment of the Phacelia, but poor establishment of the rye. Overall, there were no significant differences based on treatment for infiltration in vine rows or interrow spaces. Soil samples collected in June 2023 revealed significantly higher soil microbial biomass, stable aggregates, and extracellular polysaccharides associated with the phacelia subplot soils. Soil samples collected in June 2024 are currently being analyzed. Grape quality and yield were determined in October 2023, revealing a detrimental impact of the rye cover treatment on yield and some cluster market quality parameters. In support of Sub-objective 1B, greenhouse gas (GHG) emissions and soil carbon (C) and nitrogen (N) in an almond orchard have been monitored in field plots since 2019 following whole orchard recycling (WOR) treatments. Variances in GHG emissions in response to WOR were documented, but the properties governing woodchip (WC) decomposition are unknown. Factors impacting WC decomposition in soils, such as WC particle size, GHG emissions, and N transformation, were assayed in laboratory incubation experiments. The first experiment was conducted for eight months by incorporating WC in four sieved sizes with and without N applications. All treatments with WC showed that carbon dioxide (CO2) emissions peaked within the first week, then decreased drastically afterward. The CO2 peak delayed as the WC size increased. Nitrogen application reduced total CO2 emissions by 1% in the smallest WC size and by 8–9% for those larger than 1.6 mm. The results imply that larger WC sizes may delay C mineralization and reduce initial N immobilization risks, but increased soil organic carbon was associated with the smallest WC size. A second laboratory experiment was conducted in early 2024 to evaluate the effects of different WOR woodchip sizes, soil water content, and temperature on GHG emissions and soil N changes. Two WC sizes were selected and incubated at three soil moisture levels and two temperatures. All treatment received the same amount of N twice during ~ three-month incubation. Data were collected as in the first incubation experiment. Most measurements and soil sampling have been completed. Samples are currently under processing and analyses. For Sub-objective 1C, a WOR field trial was leveraged to collect soil samples for microcosm experiments. Soils were brought to consistent soil moisture and incubated at 25°C or 35°C and monitored using a respirometer to capture continuous CO2 flux. Subsamples of soil were stored for microbial analyses to compare active soil microbial populations at the start and end of the incubation period when the most abundant portions of labile soil organic carbon (SOC) or passive SOC are present, respectively. From the incubation results we will model the temperature sensitivity of the SOC to decomposition (Q10), the SOC pool sizes for fast, slow, and passive SOC pools, and the decomposition rates for the fast, slow, and passive SOC pools. In tandem to this we will perform similar analyses to assess the impacts of cover crops on SOC decomposition kinetics. ARS researchers in Parlier, California, intended to use a cover crop trial in Kern County, however in both 2022 and 2023 weed pressure was too high. Weed surveys revealed that planted cover crops did not outcompete weeds and bare control plots were not significantly different from cover crop plots regarding the abundance and types of weeds present. We are now leveraging a cover crop trial in almonds at Univeristy of California (UC) at Davis and will collect field soils from this trial in Spring 2025. Interactive impacts of WOR and cover crop treatments with compost will be assayed in 2026. In support of Sub-objective 2A, deficit irrigation treatments were initiated after fruit harvest. The experiment contains five drip, five fanjet, and two furrow irrigation treatments with six replications or a total of 12 plots per block and 72 plots for the orchard. Drip 1, fanjet 1, and furrow 1 treatments received 100% irrigation for the entire postharvest season and was used as the control treatments. Drip 2 and fanjet 2 treatments received 100% irrigation in growth stages I and II then reduced to 75% irrigation in stage III. Drip 3 and fanjet 3 treatments received 100% irrigation in growth stages I, increased to 125% irrigation in stage II, then reduced to 75% irrigation in stage III. Because the nectarines are targeted for fresh market, 125% irrigation was used in stage II or the fruit ripening stage to determine the possibility for increasing fruit size. Drip 4 and fanjet 4 treatments received 100% irrigation for growth stages I and II then reduced to 50% irrigation in stage III. Drip 5 and fanjet 5 treatments received 100% irrigation in growth stages I, increased to 125% irrigation in stage II, then reduced to 50% irrigation in stage III. Similar to Drip 5 and fanjet 5, furrow 2 treatment received 100% irrigation in growth stages I, increased to 125% irrigation in stage II, then reduced to 50% irrigation in stage III. Nectarine bloom and fruit set counts were measured in the spring. Leaf stomatal conductance readings were taken monthly. Fruits were harvested to determine weight per tree and total number of fruits per tree. Two fruits were taken from each tree to analyze for pH, soluble solids, skin color, and flesh firmness for one and three days of shelf life and after cold storage at 4°C for one and four weeks, respectively. Under Sub-objective 2B, the pomegranate orchard was irrigated using a surface drip irrigation system with separate flow controls for achieving individual irrigation treatment. Four irrigation treatments were used to evaluate responses to mild and severe water stress conditions. Rate of water application was based on crop evapotranspiration requirements determined from early phases of the project. Leaf stomatal conductance values were measured using a portable porometer 10 times during the growing season at day of year 130, 144, 172, 200, 228, 256, 265, 272, 279, and 286, respectively. Fruit yield and quality were determined during and after harvest in October. Total marketable fruits included both prime and superficial fruits. Fruit quality determined were external fruit surface and internal juice colors, aril size, and juice Brix and pH values. For Sub-objective 2C, a new eddy covariance (EC) tower system was established in a trellised citrus orchard at a commercial orchard near Visalia, California. The trellised citrus represents the newest production system by citrus growers in the central valley of California. It is believed that the fruit yield can be increased 300 to 400% times of the conventional citrus systems. However, it is not known how much more water would be needed. The new EC tower system will generate new data to help answer the question on water demand by the trellised citrus. Using remote sensing images, an effort was made to compare a new water and energy balance model with OpenET ensemble models for predicting citrus water use. Model predictions were evaluated against measurements with in-situ EC towers for conventional orchard systems. A manuscript was submitted and is under peer-review by the scientific journal. Under Objective 3, to evaluate physiological and yield responses to irrigation with high saline water, salt and boron (B) tolerant varieties of broccoli, lettuce, citrus varieties, cactus, agretti, guayule, perennial grass species, hybrid poplars, and young and mature pistachio trees, were grown and evaluated. Real - time changes in soil salinity with saline irrigation (ranging from 6 to 14 dS/m) and soluble B (ranging from 6 to 14 mg B/L) were measured using soil sensors. Uptake and speciation of selenium (Se), and accumulation of B, sodium (Na) and chloride (Cl) in all edible tissues, as well as the effects of salinity and B on yield (including pistachio nut and prickly pear fruit), nutritional quality, total phenolics, latex and rubber production were investigated. Tested plant species accumulated Se ranging from two to 12 mg Se/kg dry weight (DW) in plant tissues, including the seleno-amnio acid selenomethionine, and produced bio-based products, e.g., rubber, resin, edible selenium enriched plant tissues, nuts and fruit. Additionally, measurements were made to determine the amount of Se removed from soil via plant uptake and Se volatilization. For guayule grown in field tiles, Se volatilization rates were as high as 125 ug/m2/ 24 hr during the year. The highest Na accumulation among the plant species was measured in agretti at 7%, while guayule contained less than 100mg Na/kg DW. Nut yields for mature pistachio trees irrigated with saline water ranged from 300 to 2500 lbs/acre, while younger trees (six years old) produce measurable amounts of nuts. The excessive accumulation of B, Na, and salinity in soils after irrigation with saline water significantly contributed to slight decreases in yields in most crops, except in agretti and in young pistachio trees (after five years of saline irrigation). Increased soil salinity reduced the uptake of B and Se by all plants. Net losses (10-18%/year) of soluble soil Se primarily occurred at 0-45 cm in micro plots planted with grasses, guayule, poplar trees and agretti. Most of the removed Se (up to 20%) was by plant uptake, while losses of Se (~10%) also occurred due to volatilization and excessive precipitation in 2023.

Accomplishments
1. Table grape vineyard water dynamics, soil health, and vine vigor were enhanced by cover crop. Cover crops are commonly used for fallow grounds and their environmental benefits in grapes are largely unknown. To assess the utility of cover crops in table grape production in Mediterranean climates, ARS researchers in Parlier, California, compared Phacelia and Merced Rye, which are cool season cover crops, to a control consisting of vineyard alleys maintained as bare ground. Phacelia, a forb with low carbon to nitrogen ratio in plant tissues, had enhanced benefits with respect to improvements in soil microbial biomass, soil aggregate stability, and water savings. Overall, cool season cover crops increased soil health properties as well as vineyard water dynamics, but these impacts diverged based on cover crop plant traits.

2. Increased understanding of carbon (C) and nitrogen (N) dynamics with different sized woodchips. Incorporating large amounts of woody biomass into soil can promote carbon sequestration, nutrient recycling, and ecosystem health in agricultural fields. ARS researchers in Parlier, California, investigated greenhouse gas (GHG) emissions and changes in soil C and N affected by woodchip (WC) sizes and interaction with N fertilizers in an eight-month incubation experiment by incorporating WCs in four sizes with and without N applications. Results showed that the smallest WC emitted the highest level of carbon dioxide (CO2) initially, which then decreased drastically as compared to higher, maintained CO2 emissions from larger size WCs. Nitrogen fertilization triggers nitrous oxide (N2O) emission with or without WC. The smallest WC size produced the lowest N2O emissions, which suggests substantial N immobilization occurred. These findings imply that larger WC sizes may delay C mineralization and reduce initial N immobilization risks while the smallest WC size may have stabilized and increased soil organic carbon faster.

3. Whole orchard recycling (WOR) increased soil water retention and reduced nitrate leaching.. WOR is an emerging orchard removal strategy that incorporates large amounts of woody biomass back into the soil system with many potential benefits to maintain soil health and crop production sustainability. ARS researchers in Parlier, California, applied a soil hydrological model (HYDRUS-1D) to evaluate the seasonal effects of WOR on water movement and nitrogen (N) retention for a newly established almond orchard across five growing seasons (2018 to 2022). An increase in soil moisture content in the WOR treatments within the zone of application (top six-inch soil depths) and reduced N leaching was observed when compared to the unamended control. These results suggest that with WOR, irrigation can be reduced by up to 20% during the tree establishment stage with minimal effect on root water uptake. This reduction in applied water can increase farm water use efficiency, reduce operational expenses, minimize N leaching, and lessen orchard environmental impacts. These positive effects imply that WOR can potentially be a profitable strategy for orchard turnover.

4. Evaluation of crop commodities suitable for saline growing conditions. Biobased products were obtained from plants grown under saline growing conditions in field plots located in the westside of the San Joaquin Valley of California. These products included selenium-enriched pistachio nuts, prickly pear fruit, edible agretti, animal forage, and resin and rubber. These results demonstrated that young pistachio trees (6 years old) on UCB-1 and PG-1 rootstocks can be safely irrigated with saline (12 dS/m) and boron laden water (6 mg/L) for at least five years, while long-term saline irrigation with 4-6 dS/m water of mature pistachio trees on PG-1 rootstock reduced overall nut yields by 10-15% after 10 years of saline irrigation. Additionally, rubber composition in guayule and agretti yields increased with saline irrigation. Findings with young and older pistachios are significant and especially important for pistachio growers on over 550,000 acres in California, and findings from alternative salt tolerant crops like guayule, agretti, salt grass and prickly-pear are important for drought-stricken Central California when irrigation with poor quality is important to sustain irrigated agriculture.

U.S. DEPARTMENT OF AGRICULTURE

Water Management Research: Parlier, CA