Technological innovations to improve water management in alfalfa and forage crops

Authors: Evett, Steven - Steve; Oshaughnessy, Susan; ANDRADE, MANUEL - Orise Fellow; Colaizzi, Paul

Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 11/11/2018
Publication Date: 11/14/2018
Citation: Evett, S.R., O'Shaughnessy, S.A., Andrade, M.A., Colaizzi, P.D. 2018. Technological innovations to improve water management in alfalfa and forage crops [abstract]. Second World Alfalfa Congress, November 11-14, 2018, Cordoba, Argentina. p. 1.

Interpretive Summary: In the Southern High Plains, as in the rest of the U.S. Western states, water for irrigation is increasingly scarce due to declining well yields, drought and competition for water resources. Farmers can adapt by changing crops grown, tillage practices and irrigation application and management methods. Alfalfa has an undeserved reputation as a high water consuming crop, where in reality it exhibits high crop water productivity (yield per unit of water consumed), can be deficit irrigated while still maintaining profitable yields (unlike corn), and can withstand cessation of irrigation later in the season. Thus, alfalfa is a profitable crop choice under water scarcity. Further improvement in alfalfa productivity can be obtained using subsurface drip irrigation, which reduces evaporative losses and maximizes crop water productivity. Deficit irrigation of up to 20% can be practiced with little yield reduction if well managed. USDA ARS scientists and engineers at Bushland, Texas, devised a variable rate irrigation (VRI) center pivot system that allows managed deficit irrigation with little labor. The system relies on wireless soil and plant sensor systems also devised by the Bushland scientists and developed into commercial products through cooperation with manufacturers in Texas and Idaho. These sensors have been integrated into an automated VRI center pivot decision support system that allows farmers to apply irrigations according to a prescription at the click of an icon, reducing farmer labor to a minimum while making the best use of scarce water resources.

Technical Abstract: In the US, 40% of crop market value is produced by irrigation on only 7.5% of cropped lands, but progress is frustrated by present and likely future water shortages. To sustain and improve agricultural productivity requires increases in irrigation efficiency and crop water productivity (CWP), also known as water use efficiency. Irrigation efficiency is the ratio of water consumed by the crop through evapotranspiration (ET) to the irrigation water applied. Reducing runoff and deep percolation losses are ways in which to increase irrigation efficiency. Water use efficiency (WUE) or crop water productivity (CWP) is defined as the economic yield obtained per unit of water consumed by the crop: CWP = Y/(E + T) = transpiration efficiency/(E/T + 1); where Y is economic yield, E is evaporation, T is transpiration, and the transpiration efficiency is Y/T. Ways to change CWP include choice of crop and variety (affects Y/T), irrigation scheduling and amount, irrigation method and management, fertility management, tillage management and soils and climate. Timing of water supply has a large effect on CWP. An otherwise well-watered crop that is short of water during a critical growth period will suffer decreased yield and CWP. Irrigation method can influence WP by affecting the ratio of evaporative loss to crop transpiration. Irrigation methods that reduce soil and crop wetting, and thus evaporative losses, include subsurface drip irrigation and low-energy-precision-application (LEPA) applicators on sprinkler irrigation systems. Forage yields are as reliant on a stable water supply for increases in yield and CWP as are yields of grain crops. In the western US (largely west of the 95th meridian), non-irrigated forage yields are roughly 1 ton/acre less than those in the eastern states. However, in the western states where >31% of forage lands are irrigated, yields are roughly three times greater than those achieved on non-irrigated lands and considerably larger than those achieved in the eastern US where most forage is not irrigated. Sprinkler systems equipped with low-elevation-precision-application (LEPA) and low-elevation-spray-application (LESA) devices can reduce evaporative loss from wetted canopies and to some extent from soil surfaces when used in every other crop interrow, but can cause runoff problems. Subsurface drip irrigation (SDI) eliminates losses from canopy wetting and most losses due to evaporation from the soil surface, resulting in increased crop water productivity and allowing high yields with less water pumped. In some cases, yields are larger with SDI than are possible even with full irrigation using gravity methods. Advanced irrigation systems utilizing wireless sensor systems to automatically determine crop water stress have been shown to improve crop water productivity and allow well-regulated deficit irrigation with little user effort. When used with variable rate irrigation systems, these advanced supervisory control and data acquisition (SCADA) systems can allow spatially varying application of irrigation water to avoid flooding low lying areas and to respond to water stress where it occurs in the field. Combined with ever improving wireless plant and soil water sensing systems, SCADA control is poised for rapid commercialization and application in producer fields.