Location: Water Management and Systems Research
2018 Annual Report
Objectives
1. Improve water use efficiency (WUE) by identifying plant traits, mechanisms, and agronomic practices that increase productivity per unit of water used by the crop.
2. Develop simple and accurate methods to quantify evapotranspiration (ET) in agricultural systems under limited water availability to improve the efficiency of irrigation scheduling.
3. Create Water Production Functions (WPF, yield per ET) for alternative crops under limited water availability.
Approach
Increased productivity of cropping systems as well as yield stability is vital to meet the challenge of expanding human populations and increased needs for food and fiber. Effective management of cropping systems and irrigation water will depend on our ability to maximize crop water productivity (yield per unit water used by the crop). This, in turn, requires a better understanding and evaluation of complex plant traits, better management of interacting agricultural inputs, and better tools to more efficiently manage agricultural water supplies, especially in the face of greater competition and less water availability. Finally, there is increased efficiency at the farm scale that can be realized with better farm-scale decision making. The overarching goal of this research is to improve the sustainability of irrigated farming systems for agronomic producers in semi-arid and arid regions. These producers vary both in control over the timing and amount of irrigation, and in methods of irrigation; thus multi-faceted solutions are required. Solutions are in three parts: 1) increasing the knowledge base of plant traits, mechanisms and agronomic practices related to crop productivity under limited water; 2) developing tools to assist with real-time decision making for irrigation management; and 3) developing information and tools for farm-scale decision-making regarding crop selection, land area partitioning among crops, and within-farm irrigation distribution. This research will lead to better understanding of crop physiology needed to improve germplasm, increased productivity of cropping systems, and improved irrigation management.
Progress Report
Objective 1: Six sorghum lines that varied in growth under drought were grown in the greenhouse under either full water or drought to examine physiological mechanisms underlying their growth responses to water availability. The lines were assessed for growth, photosynthesis, respiration, stomatal conductance, electron transport, cell membrane stability, root pressure, and xylem cavitation. Results suggest that root pressure was actively regulated by the plants and increased by drought treatment. Further analysis of the data is ongoing. Eight maize genotypes varying in drought tolerance and yield stability under drought were planted in the field across three irrigation treatments, with each genotype by irrigation treatment replicated four times. Treatments are being implemented. We will assess root pressure as a mechanism for sustaining plant turgor during anthesis and increasing productivity under drought. 125 accessions of winter wheat were evaluated in the field for growth rate, photosynthesis, and stomatal conductance under well-watered and deficit conditions. Xylem tissue was sampled from leaves and is currently being processed for vessel diameter, vessel number, and the calculated rate of theoretical conductance. In addition, 100 inbred maize genotypes were evaluated for the same performance and xylem traits as listed above for winter wheat. These two experiments will help evaluate the proposed phenotypic and genetic links between water transport traits and improved performance under deficit irrigation. An experiment on maize with three levels of nitrogen and two levels of water availability was established in the field and instrumented to examine root growth, soil emissions, and leaching. Measurements are underway to assess plant responses, nitrogen losses, and interactions with the soil microbial community.
Objective 2: Analyzed remote sensing imagery with an unmanned aircraft system for 8 maize genotypes under three levels of water availability from 2017 and collected similar data in 2018. A hex-copter integrated with a multispectral camera and a thermal camera was used to collect 6-band multispectral and thermal imagery one or two days before the scheduled irrigation day from each plot. We processed multispectral imagery to get canopy cover within 24 hours to assist in determining irrigation amount. Canopy temperature measured by thermal imagery and vegetation indices from multispectral imagery will be used to explain the response of different maize genotypes to water treatment. Data processing was streamlined, and variation and abnormities among sampling dates managed to enable bi-weekly data analysis.
Objective 3: A field experiment with sorghum under five levels of water availability from fully irrigated to rain-fed was established. Data collection of crop development, water use, and yield is in progress.
Accomplishments
1. Determined effects of strategic deficit irrigation on maize grain yield and assessed the economic impacts. In arid areas where agriculture is dependent on irrigation, various forms of deficit irrigation management have been suggested to achieve high yields with less water. ARS scientists in Fort Collins, Colorado, showed water savings of 15-17% with little impact on yield by applying moderate deficit during the late-vegetative stage (prior to flowering). Importantly, these late-vegetative deficits prevented dramatic yield losses if water shortages occurred at the end of the season. Economic modeling found little benefit to producers of intentionally applying deficit irrigation under current average grain and water prices, but that deficit irrigation during the late-vegetative stage would be economical in some regions with high demands on water and rising lease prices. Thus, while strategic deficit irrigation showed some, but limited, benefit for producing yield with less water, the most important benefits to producers resided in protecting crops against yield losses in response to late-season water shortfalls. These results benefit producers by indicating the conditions under which deficit irrigation may be desirable. These results benefit water conservation districts and policy makers by providing the economic thresholds for policies that can be implemented to balance agricultural and municipal water interests.
2. Improving water transport and drought tolerance in the leaves of crop species. Improving the capacity of crops to transport water is critical to improving crop performance because plants must transport water to leaves for growth to occur. However, it is poorly understood which specific water transport traits achieve this outcome. ARS scientists in Fort Collins, Colorado, used an existing dataset that reported water transport traits in the leaves of 36 plant species growing under varying water availability. They discovered that natural selection resulted in vessel traits that delivered maximal hydraulic conductance for a given amount of material and energy invested in the vascular network. Importantly, the size and number of vessels scaled similarly with plentiful and limited water conditions, but greater conductance was achieved in all cases (wet or dry) via fewer but wider vessels at the base of leaves. This suggests that plant breeding programs aimed at increasing hydraulic conductance per unit leaf area will need to increase the diameter of vessels in petioles, but that the scaling of vessel size and number from the petiole to the sites of photosynthesis will need to adhere to a very specific scaling coefficient. Results are being incorporated into breeding programs to improve germplasm for both winter wheat and maize.
Review Publications
Zadworny, M., Comas, L.H., Eissenstat, D.M. 2018. Linking fine root morphology, hydraulic functioning, and shade tolerance of trees. Annals of Botany. 122(2):239-250. doi:10.1093/aob/mcy054.
Comas, L.H. 2017. Exploring plant root traits and fungal interactions governing plant community structure: Re-focusing long standing questions. New Phytologist. 216:963-964.
Trout, T.J., Dejonge, K.C. 2018. Crop water use and crop coefficients of maize in the US Great Plains. Journal of Irrigation and Drainage Engineering. 144(6):04018009. doi:10.1061/(asce)ir.1943-4774.0001309.
