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

Location: Water Management Research

2023 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
Under Sub-objective 1A, a table grape vineyard with two alleyway cover crop treatments and a bare alley control were established in 2019 at the USDA-ARS San Joaquin Valley Agricultural Sciences Center in Parlier, California. To address California growers’ concerns that table grape vineyard cover crops compete with vines for soil water and nutrients and become weedy, we quantified soil water infiltration, soil biological and chemical properties, weed pressure, and grape quality and yield. There was not a significant impact of cover crops in alleys or vine rows on water infiltration. During most seasons the weed percent cover was also not impacted by cover crops, with the exception of one spring season, when weeds were significantly lower in alleys of both cover crop treatments compared to the bare alley control, and in one summer season when the introduced cover treatment plots had higher weed coverage in vine rows. The Lacy Phacelia cover crop treatment had higher soil microbial biomass in vine rows and in alleyways than did the ‘Merced’ rye cover. Vine vigor estimates also demonstrated positive benefits of the Phacelia cover with potential negative benefits of the Merced Rye on trunk diameter and dry pruning weight. Marketable yield of table grapes was not significantly impacted by cover crop treatments, nor were most quality indicators, except for berry shatter, a detrimental market trait, that was reduced in the Phacelia cover cropped plots. Therefore, planting cover crops can potentially benefit table grape production. In support of Sub-objective 1B, greenhouse gas (GHG) emissions and soil carbon (C) and nitrogen (N) dynamics in two almond orchards were monitored. Orchards were established following whole orchard recycling (WOR) treatments. WOR refers to a new practice of turning all tree biomass into woodchips and incorporating them into soil following orchard removal. WOR can sequester carbon, improve soil properties, and return nutrients as well as reduce immediate GHG emissions as opposed to burning or hauling to cogeneration plants, which has been the most used practice in orchard waste disposal for decades. There were many unknowns on WOR that needed to be addressed to maximize its benefits. This research focuses on better understanding of C and N dynamics. One of the orchards was a commercial field and GHG emissions were measured since early 2018 after its establishment. The other orchard at University of California Kearney Agricultural Research and Extension Center (UC KARE) in Parlier was monitored similarly since establishment in early spring 2019. Both fields included high woodchip incorporation rate at 60-80 t/ac and control plots without woodchips for comparisons. In the UC KARE field, different N fertilizer application rates were also included. Three major GHG emissions including carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) were measured year-round in two different locations: tree rows and alleyways. Results showed significantly higher CO2 and N2O emissions from woodchip treatments than no-woodchip control. CO2 and N2O emissions were most dynamic and influenced by different factors or field activities while CH4 emissions remained extremely low in both orchards at all times. CO2 emissions were the highest following woodchip incorporation and reduced significantly with time. Estimation from the first three years of data showed CO2-C emissions were about 40% and the emissions were significantly higher from irrigated tree rows than in alleyways (between tree rows). N2O emissions were largely impacted by fertilization events and woodchips enhanced the emission process. Temporal and spatial variations observed due to irrigation, precipitation, and fertilizer application or fertigation demonstrated challenges in the accuracy in estimating total GHG emissions from the orchards. Field monitoring continues to address the temporal and spatial variations in GHG emissions. Under Sub-objective 1C, cover crops were seeded in the interrow spaces of an almond orchard in McFarland, California, in October 2022 and established in late winter/early spring. However, native vegetation was dense in the unplanted control plots and cover crop treatments. Hence, we collected soil samples for baseline analysis. Soil analysis will be done next year after all the samples are collected. Soil from a second orchard, wherein woodchips were incorporated into soil in 2017 as part of a WOR study, will be used to evaluate interactive impacts of soil carbon building practices and compost (e.g., “stacked practices”). Spring and summer sampling of the WOR field site will be deferred to occur when compost is typically applied in Central Valley orchards. To expand on this project, samples were collected in the spring from the WOR site and were incubated at either 25 or 35°C with continuous measurement of soil respiration. Data collected from the study will enable modeling of estimated soil organic carbon (SOC) decomposition parameters and temperature sensitivity of SOC in WOR treated and non-treated plots. In support of Sub-objective 2A, a SoilVue time domain reflectometry (TDR) system was installed in one of the six replications of the nectarine orchard at the USDA-ARS San Joaquin Valley Agricultural Sciences Center in Parlier, California. The irrigation schedule was based on TDR soil moisture sensor readings by maintaining 18 to 25% volumetric water content in the tree root zone. Water was applied uniformly through furrow, micro-sprinkler, and drip irrigation systems. Nectarine bloom and fruit set counts were taken by irrigation treatment in the spring. Periodic leaf stomatal conductance readings were taken using a portable porometer. Fruit harvest was made to determine weight per tree and total number of fruits per tree. Sub-samples of fruits were taken to analyze for pH, soluble solids, and fruit firmness after cold storage at 4 degrees Celsius for one and four weeks, respectively. Data analysis is ongoing and results will help farmers to optimize irrigation management to improve water use efficiency, fruit yield and quality. In support of Sub-objective 2B, four irrigation treatments were initiated to evaluate pomegranate response to mild and severe water stress conditions. Rate of water application is based on crop evapotranspiration (ETc) requirements determined from early phases of the project. A computer algorithm was created to obtain daily reference ET from a nearby weather station and compute ETc for the pomegranate trees. The entire orchard is irrigated using a surface drip irrigation system with separate flow controls for each treatment. Soil moisture sensors were also used to monitor soil water content in the plant root zone in real-time. Leaf stomatal conductance values were measured using a portable porometer at pre-selected phenological growth stages of the trees. Fruit yield and quality will be determined in late October or November. Similar to the previous year, the orchard was pruned minimally this year following recommendations by our stakeholders. The goal is to maximize canopy size and tree volume for potential higher yield in subsequent seasons. Under Sub-objective 2C, models in the OpenET ensemble were compared for accuracy in estimating citrus ET. The cropland data layer from the National Agricultural Statistical Service or NASS was imported into OpenET to obtain spatial data for citrus within the study region. Average citrus ET was the lowest from November to February with a mean value of about 30 mm per month, and highest from May to August with a mean value of about 125 mm per month. Predicted ET from the five models in OpenET was also comparable. The preliminary findings demonstrated that the satellite-based models can provide reasonable ET estimate for citrus. In support of Objective 3, research continues successfully on evaluating salt and boron (B) tolerant varieties of cactus, agretti, guayule, perennial grass species, hybrid poplars, and young and mature pistachio trees, for physiological and yield responses to irrigation with high saline water (ranging from 6 to 14 decisiemens per metre (dS/m)), and soluble B (ranging from 6 to 14 milligrams per liter (mg B/L)). In collaboration with other ARS and university researchers, we are evaluating effects of saline irrigation water on latex and rubber production and quality in guayule and in pistachio nuts. The tested plant species accumulated selenium (Se) ranging from 2 to 8 mg Se/kg and produced bio-based products, e.g., rubber, edible Se enriched plant tissues, including nuts and fruit. Additionally, measurements were made to determine the amount of Se removed from soil via plant uptake and Se volatilization. For guayule, volatilization rates were as high as 100 micrograms per meter squared per 24 hour period. Among the plant species, agretti accumulated sodium (Na) concentration as high as 5 percent (%), while mature pistachio leaves contained B and Na as high as 5000 and 7000 mg/kg, respectively. Nut yields for mature pistachio trees irrigated with saline water ranged from 500 to 2200 lbs/acre. The excessive accumulation of B and Na in the soil contributed to slight decreases in yields in most crops, except in agretti; salinity stimulates yield by as much as 15%. Interestingly, in all studies, the higher the soil salinity the lower the accumulation of B in the plants. Importantly, net losses of soluble soil Se at 0-45 cm ranged from 5-15% one year in micro plots planted with grasses, guayule, poplar trees and agretti; 15% of the lost Se was accounted for in harvested plant material, while more than 10-15% was assumed lost by leaching with excessive precipitation in 2022. These results showed that the tested plant species can be grown under saline conditions with high concentrations of Se and B.

Accomplishments
1. Soil biochar application affects microbes and nitrogen retention. Soil amendment with biochar increases carbon storage but effects on microbial community and nitrogen dynamics are less understood. ARS researchers in Parlier, California, evaluated the impact of biochar soil incorporation on nitrogen (N) transformation processes and underlying microbial mechanisms. They revealed that soil moisture was a critical factor affecting N transformation processes and biochar offered some pH buffering potential, a benefit for reducing soil acidification associated with some N fertilizers. However, co-application of biochar with manure composts enhanced nitrification, which may be undesirable. Therefore, soil moisture plays a vital role in reducing fertilizer N losses in biochar and manure compost amended soils. Policy makers and growers aiming to improve soil N retention and reduce nitrate leaching using biochar soil amendment should consider all soil environmental conditions prior to scheduling fertilization.

2. Salt tolerant rootstocks for pistachios. Increased demand and production of pistachios in California rely on irrigation, but saline water may be used due to lack of fresh water, and there is a need to know the degree of tolerance to salinity by newly planted pistachio trees. Pistachio growers on over 350,000 acres in California need to know when and how long they can safely apply other sources of water. An ARS researcher from Parlier, California, demonstrated that young pistachio trees (less than five years old) on UCB-1 and PG-1 rootstock could be safely irrigated with saline and boron-laden water for at least three years, while long-term saline irrigation of mature pistachio trees reduced overall nut yields by 10-15 percent. These findings clearly demonstrate that California pistachio growers can safely irrigate their trees with saline and boron water without significantly impacting the establishment of the young trees or nut yields of the mature trees.

Review Publications
Banuelos, G.S., Placido, D.F., Zhu, H., Centofanti, T., Zambrano, M., Heinitz, C.C., Lone, T.A., McMahan, C.M. 2022. Guayule as an alternative crop for natural rubber production grown in B- and Se-laden soil in Central California. Industrial Crops and Products. 189. Article 115799. https://doi.org/10.1016/j.indcrop.2022.115799.
Hale, L.E., Hendratna, A., Scott, N.M., Gao, S. 2023. Biochar enhancement of nitrification processes varies with soil conditions. Science of the Total Environment. 887. Article 164146. https://doi.org/10.1016/j.scitotenv.2023.164146.
Silva, M.A., Ferreira De Sousa, G., Banuelos, G.S., Amaral, D., Brown, P., Guimaraes Guilherme, L.R. 2023. Selenium speciation in Se-enriched soybean grains from biofortified plants grown under different methods of selenium application. Foods. 12(6). Article 1214. https://doi.org/10.3390/foods12061214.
Wen, T., Ding, Z., Thomashow, L.S., Hale, L.E., Yang, S., Xie, P., Liu, X., Wang, H., Shen, Q., Yuan, J. 2023. Deciphering the mechanism of fungal pathogen-induced disease-suppressive soil. New Phytologist. 238(6):2634-2650. https://doi.org/10.1111/nph.18886.
Bolan, S., Hou, D., Wang, L., Hale, L.E., Egamberdieva, D., Tammeorg, P., Li, R., Wang, B., Xu, J., Wang, T., Sun, H., Padhye, L.P., Wang, H., Siddique, K., Rinklebe, J., Kirkham, M., Bolan, N. 2023. The potential of biochar as a microbial carrier for agricultural and environmental applications. Science of the Total Environment. 886. Article 163968. https://doi.org/10.1016/j.scitotenv.2023.163968.
Hall, J.A., Bobe, G., Filley, S.J., Pirelli, G.J., Bohle, M.G., Wang, G., Davis, T.Z., Banuelos, G.S. 2023. Effects of amount and chemical form of selenium amendments on forage selenium concentrations and species profiles. Biological Trace Element Research. 201:4951-4960. https://doi.org/10.1007/s12011-022-03541-8.
Hall, J.A., Bobe, G., Filley, S.J., Pirelli, G.J., Bohle, M.G., Wang, G., Davis, T.Z., Banuelos, G.S. 2023. Effects of amount and chemical form of selenium amendments on forage selenium concentrations and species profiles. Biological Trace Element Research. 201:4951-4960. https://doi.org/10.1007/s12011-022-03541-8.
Wang, M., Zhou, F., Cheng, N., Chen, P., Ma, Y., Zhai, H., Qi, M., Liu, N., Lui, Y., Meng, L., Banuelos, G.S., Liang, D. 2022. Soil and foliar selenium application: Impact on accumulation, speciation, and bioaccessibility of selenium in wheat (Triticum aestivum L.). Frontiers in Plant Science. 13. Article 988627. https://doi.org/10.3389/fpls.2022.988627.