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

Location: Water Management Research

Project Number: 2034-13000-013-000-D
Project Type: In-House Appropriated

Start Date: Jan 29, 2022
End Date: Jan 28, 2027

Objective:
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.