Project : USDA ARS

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Research Project: Optimizing Water Use Efficiency for Environmentally Sustainable Agricultural Production Systems in Semi-Arid Regions

Location: Wind Erosion and Water Conservation Research

2020 Annual Report

Objectives
Obj 1: Quantify the environmental factors that affect the degree of crop drought stress. Sub-obj 1A Assess the effects of rising atmospheric CO2 concentration on crop coefficients used in deficit irrigation scheduling systems. Sub-obj 1B Relate seasonal plant stress and water use efficiency responses of crop plants to irrigation scheduling techniques using stable carbon isotope discrimination. Sub-obj 1C Identify active root areas under sub-surface irrigation to determine optimal cultivar for dryland management. Obj 2: Develop crop management strategies that enhance water use efficiency. Sub-obj 2A Quantify the effects of wind speed, tillage management, and irradiance on surface water evaporation. Sub-obj 2B Identify changes in microbial and chemical characteristics that may impact water availability and productivity in dryland production. Obj 3 Develop a framework of methods and models for quantifying and studying the risks associated with water from rainfall for dryland agriculture over the Southern High Plains and other dryland agricultural regions. Sub-obj 3A Evaluate the ability of current weather generator configurations to reproduce the distributional characteristics of Southern High Plains summer weather variability. Sub-obj 3B Run calibrated and validated cotton and sorghum crop models with both observed and stochastically generated weather inputs to generate simulated dryland yield outcomes. Sub-obj 3C Convert modeled yield outcomes generated with simulated weather data into net profit outcomes to form corresponding profit distributions for dryland cotton and sorghum production. Obj 4: Evaluate management practices that prevent soil degradation by soil erosion in semiarid cropping and rangeland systems. Sub-obj 4A Investigate soil redistribution & dust emissions from agro-ecosystems including rangelands & native plant communities under the stressors resulting from climate change. Sub-obj 4B Evaluate management systems in terms of multi-decadal erosion rates estimated from radioisotope inventories. Obj 5: Evaluate management practices to increase soil water availability and contribute to higher water and nutrient use efficiencies. Sub-obj 5A Partitioning of evapotranspiration to water evaporation from soil & crop surfaces for dryland & irrigated cropping systems across different N fertilizer management strategies. Sub-obj 5B Investigate changes in groundwater quantity & quality that may affect cropland production in semiarid & arid regions. Obj 6: Develop management practices that contribute to maintaining microbial diversity and functions needed to improve soil health, ensure ecosystem sustainability, and maintain crop productivity under a changing climate. Sub-obj 6A Compare the effects of different management practices in semiarid regions on soil health indicators including the microbial community size, diversity & functions. Sub-obj 6B Characterize the effects of climatic events on soil health & the effects of future climate change (CO2, temperature and rainfall) on agro-ecosystems by measuring root biomass, soil microbial diversity & soil organic matter pools.

Approach
Sustainable agriculture, with emphasis on conservation of natural resources, is a challenge in the semiarid climate of the Southern High Plains (SHP). Of concern is developing cropping systems that cope with climate change, depletion of aquifers used for irrigation, and growing seasons characterized by frequent droughts and erratic rainfall. Climate change is expected to impose general global challenges but, clearly, solutions to these problems will be site specific. Within a framework to quantify and study the risks associated with dryland agriculture, we need sustainable agricultural systems that optimize productivity, conserve water, control soil erosion and improve soil health for agricultural production in semiarid regions and in a changing climate. We will continue long-term research that identifies management practices that impact water availability in dryland farming vs. lands in the Conservation Reserve Program. Our goal is to provide agricultural producers with tools to manage limited water resources in the semi-arid environment of the SHP. New technologies for exposing crops in the field to elevated levels of atmospheric CO2 concentration will be used to monitor hourly and daily whole canopy water use efficiency by simultaneously measuring the ratio of net CO2 assimilation to evapotranspiration. Optimum irrigation scheduling techniques will be determined from stable carbon isotope discrimination while optimal cultivars for dryland agriculture will be selected by identifying and comparing active rooting areas. This multifaceted research program will provide the knowledge base for optimizing the use of scarce water resources in arid and semi-arid regions where ground water resources are being depleted.

Progress Report
Our team made considerable progress in studies related to: data management and modeling; soil and dust samplings; and in greenhouse experiments. For example, within Objective 1, two complete growing seasons studying the effects of elevated atmospheric carbon dioxide (CO2) concentration on peanut and cotton were completed. Results from these experiments will provide information on the effects of rising CO2 concentration on crop coefficients used in deficit-irrigation scheduling systems. Twenty-five diverse cotton isolines with dates of introduction spanning a century were grown in the field under controlled deficit irrigation. In addition, genetically modified cotton with selected traits thought to affect water use efficiency were grown. Leaves were processed for stable carbon isotope analysis. We will continue with the extraction of cotton seed oil and the processing of cotton leaves and seeds from a single cultivar grown under several irrigation regimes when we return to work. Additionally, we built a prototype instrument to measure soil water content with a circular array of sensors. This is part of studies to identify active root areas under sub-surface drip irrigation to determine an optimal cultivar for dryland management. We modified polyvinyl chloride pots with 3-D printed ports that can be inserted into the pot at varying heights. Various 3-D printed ports were designed and tested to allow free water flow through the end of the port without allowing the sand and fritted clay to enter and clog the port. A 2 x 5 cm filter paper was found to be the smallest size that would absorb enough water for the isotopic extraction and analysis. We were able to determine that the minimum time to achieve full extraction of the water collected was 30 minutes. This is an important finding as the fast extraction time will facilitate processing the large number of samples that will result from these experiments. Accordingly, as we return to work we will resume the greenhouse and laboratory experiments from this objective. Within Objective 2, studies to identify changes in soil microbial and chemical characteristics that impact water availability in dryland production could not proceed as originally planned and were modified. For example, weekly measurements of soil water content measured with neutron probes that were going to be used to establish linkages to water infiltration were discontinued. These measurements are taken throughout the growing season in producer’s fields and are laborious. Thus, we shifted to quantify the spatial variability between water isotopes and microbial activity, and to establish a covariance of these measurements that could lead us to identify how they are related to each other. We made significant progress in completing the laboratory analyses of previously collected soil samples from two of the three fields that were part of this experiment. As part of Objective 3, we used crop simulations of the U.S. Southern High Plains (SHP) dryland sorghum and cotton production, a profit and risk analysis based on the resulting climate-representative yield distributions were converted into corresponding profit distributions reflecting 2005–2019 Texas commodity prices and 2018 production costs. Profitability of the two crops was compared in terms of median profits and loss probability, through a stochastic dominance analysis that assumed a slightly risk-averse producer. During fiscal year 2020 collaborative research efforts resulted in modeling effects of temperature and humidity on cattle mortality in SHP feedlots. The results of a second collaborative effort focused on the simulated water balances of two major SHP soil types. Other collaborative research during the fiscal year simulated the effects of soil organic matter on soil water capacity and dryland cotton yields using the Decision Support System for Agrotechnology Transfer Crop Grow (DSSAT CROPGRO)-Cotton crop model. For Objective 4, our analysis of dust emission data from a field campaign sampling cropped and native range soil surfaces in five Southwestern states using a portable wind erosion instrument, i.e., Portable In-Situ Wind ERosion Lab (PI-SWERL) was accomplished during the first 4 weeks of telework. This data, including critical parameters of threshold wind speed, maximum dust emissivity, and supply limitations, which was disseminated to two teams of university scientists working on dust emission models using remotely sensed aerodynamic roughness estimates. Maximized telework precluded the travel to the study site (Sevilleta National Wildlife Refuge) to collect samplers in the shrubland plant community and post-fire re-installation of sampler masts in the grassland. Within this objective, as part of a multi-location ARS study of soil change, researchers are preparing, extracting and scheduling chemical analysis of anthropogenic radioisotopes to estimate decadal scale soil redistribution that may be causing the changes in soil properties in the last 7 decades. One of our scientists was selected as an expert in a scientific advisory panel of the National Academies of Science, Engineering, and Medicine by a court mandated to arbitrate a dispute between two governmental parties with responsibility to remediate Owens Dry Lake, at one time North America's largest single dust source. To accomplish Objective 5, there are different studies related to partitioning of evapotranspiration to water evaporation from soil and crop surfaces for dryland and irrigated cropping systems across different N fertilizer management strategies. For one of the studies, we established numerous groundwater and surface water sampling sites east of the SHP. Samples were collected each month for laboratory analysis and in-situ measurements of temperature and dissolved oxygen, and additional chemical data were obtained from the Texas Commission on Environmental Quality (TCEQ). In addition, we measured spring flow rates and water chemistry at Dickens Springs and at Silver Falls in Crosby County. A new stock pond (cattle tank) study at the Yellow House Ranch in Hockley County, Texas revealed that water quantity and quality vary seasonally and is influenced by rainfall and runoff in the watershed. We also have studies, as part of Objective 5, to improve the use of rainfall for crop production by quantifying each element of the water balance to maximize the amount of rainfall that can be stored in the soil and to minimize runoff. This analysis was done using a mechanistic model applied to a bare soil with no crop and for three rainfall scenarios (below average, average and above average) for two major soil types of the SHP (Amarillo and Pullman series). Results showed that for years with average and above average (wet) rainfall, only soils in the Pullman series could store water. However, in the Amarillo soils, storage could be enhanced using furrow dikes, minimum tillage along with cover crops that minimize evaporative losses of water from the soil surface. We continue to develop mechanistic models to quantify the process of rainfall storage in the soil. Within Objective 6, frequent samplings from several producer’s sites across the SHP are providing us with an opportunity to evaluate different management practices including a transition to no-tillage. For example, we identified 13 sites, representing more than 10,000 acres, through a producer will provide a comparison of different combinations of cover crops and no-tillage. Additionally, sampling every year since 2011 at five producer's fields in Lamb County under similar cotton-management enable us to quantify the effect of climate on the soil microbial community. Our frequent samplings showed decreases in the community during 2016, which was a very warm year. Subsequent samplings in 2017, 2018 and 2019 demonstrated a remarkable resilience of the soil microbial communities in these semiarid soils.

Accomplishments
1. Dryland sorghum production may be a profitable alternative to dryland cotton production in the U.S. Southern High Plains. During 2012-2018 an average of 64% of planted cotton acres on the U.S. Southern High Plains (SHP) were not irrigated and that fraction may increase as the Ogallala aquifer continues to decline. Because of the region’s risky agricultural production conditions and increasing reliance on rainfall to maintain profitability, producers need to know which rainfed crops and management practices are best for the SHP summer climate and environment. To determine best practices for the region’s two leading rainfed crops – cotton and sorghum – an ARS scientist from Lubbock, Texas, used Texas Tech University Mesonet weather data and crop simulation models to determine the crop’s best planting dates and compare their profitability under rainfed conditions. The highest average cotton lint yields resulted from April 24 planting dates, while July 1 planting produced the highest average sorghum yields. Although sorghum is normally a secondary crop for SHP rainfed producers, these model simulations suggest that it may be more profitable and less risky than cotton under certain sorghum price conditions. As a result, SHP rainfed cotton farmers might consider planting sorghum, or combining cotton with sorghum production, to stay profitable without irrigation.

2. Spring discharge investigation reveals seasonal patterns of irrigation. In the late 19th century, many large cattle ranches were established in West Texas along the breaks at the eastern edge of the Llano Estacado. These ranches were located near spring-fed streams that provided a reliable supply of water in a region with otherwise limited water resources. Large-scale irrigation has altered hydrological conditions across the High Plains region, which has influenced the flow of springs along the eastern edge of the Llano Estacado. ARS scientists from Lubbock, Texas, obtained measurements of spring flow rates over a period of seven years. These measurements did not show an appreciable reduction of spring discharge associated with the depletion of the Ogallala aquifer, as might be expected. However, spring discharge was found to follow a seasonal pattern of declining flow during the summer growing season followed by a recovery starting in late fall and reaching maximum discharge during winter and early spring. This result suggests that irrigation of cropland on the high plains of the Llano Estacado can influence the flow of ephemeral streams in the ranchlands to the east of the Llano Estacado. These seasonal effects can reduce the amount of water available to cattle ranches located downstream of the Southern High Plains.

3. Pullman soils are suited for dryland production as they can store rainfall in years with average and above average rainfall. Dryland production continues to increase in the Texas High Plains (THP) due to a decline in irrigation-water from the Ogallala aquifer. A strategy to minimize the impact of the decline on crop yields across the region is to maximize the use of rainfall by reducing runoff and increasing storage of water in the soil. The end result from this transition to more dryland production is the increased dependency of crop yields on the amount of rainfall captured and stored in the soil profile. Scientists from Lubbock, Texas, used a simulation model to evaluate the daily water balance and the impact of a dry (7 inches), an average (18 inches) and a wet (26 inches) year of rainfall for two major soil types of the THP, Pullman in the north and Amarillo in the south. Results showed that for an average and wet year the Pullman soils can store water from the rainfall. However, this was not the case for the Amarillo soils. Nevertheless, management practices such as minimum tillage and ground cover residue can be used to enhance the capture of rainfall and assure adequate soil water to successfully grow crops. This has important implications for dryland production in the THP and shows the importance of minimizing evaporative losses of water from the soil by using residue covers, particularly in the southern region of the THP.

4. Biological indicators of soil health showed remarkable resilience after an extreme drought. Soil health and conservation initiatives agree that higher microbial abundance and activity are indicative of a healthier soil following the “more-is-better” model. Scientists from ARS in Lubbock, Texas, and Agriculture and Agri-Food Canada in Harrow, Ontario, assessed the effect of climate variability on different biological indicators of soil health (e.g., microbial community size and enzyme activities involved in nutrient cycling). The five-year study evaluated five sites under continuous cotton from the Texas High Plains semi-arid region. The sites differed in irrigation practices (drip, pivot and dryland), and soil textural class (e.g., from sandy loam to clay). Soil health indicators declined at all sites in response to decreased precipitation and increased temperatures from 2015 to 2016. However, as conditions improved, the evaluated indicators showed increasing trends within 1-2 years demonstrating a remarkable resilience. Our study highlights the need for implementing sustainable agricultural systems that optimize productivity, and conserve water to maintain soil health in a changing climate.

U.S. DEPARTMENT OF AGRICULTURE

Wind Erosion and Water Conservation Research: Lubbock, TX