Soybean irrigation initiation in Mississippi: Yield, soil moisture, and economic response

Authors: PRINGLE, H - Mississippi State University; FALCONER, L - Mississippi State University; Fisher, Daniel; KRUTZ, L - Mississippi State University

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2018
Publication Date: 1/19/2019
Citation: Pringle, H.C., Falconer, L.L., Fisher, D.K., Krutz, L.J. 2019. Soybean irrigation initiation in Mississippi: Yield, soil moisture, and economic response. Applied Engineering in Agriculture. 35(1):39-50.

Interpretive Summary: Irrigated acreage is expanding and groundwater supplies are decreasing in the lower Mississippi Delta, and conservation efforts are needed to sustain groundwater resources. Determining at what point in the growing season to initiate irrigations can help prevent over- or under-irrigation, which can lead to moisture stress and reductions in crop yield and economic return. Researchers with Mississippi State University and the USDA ARS Crop Production Systems Research Unit at Stoneville, MS, undertook a four-year study to develop irrigation initiation recommendations for soybean grown in the Mississippi Delta region based on plant growth stage, soil-moisture measurements, and estimates of soil-water deficit. These parameters were evaluated to determine which better predicted when to initiate irrigations to avoid moisture stress and reduce water use, and determine impacts on yield and economic return. A wide range of soil-moisture and soil-water deficit values over the four-year period at which irrigation initiation occurred indicated that a single threshold value is not sufficient to optimize irrigation scheduling and maximize soybean yield with the least amount of water every year. These results suggest that additional plant-based or atmospheric information may be needed in conjunction with soil-moisture or soil-water deficit data to better predict the timing of irrigation initiation of soybean in this region.

Technical Abstract: Irrigated acreage is expanding and ground water supplies are decreasing in the Mississippi Delta, USA. Efficient irrigation scheduling of soybean [Glycine max (L.) Merr] will aid in conservation efforts to sustain ground water resources. The objective of this study was to develop irrigation initiation recommendations for soybean grown on Mississippi Delta soils. Field studies were conducted on a deep silty clay (SiC) in 2012, 2013, 2014, and 2015 and on a deep silty clay loam (SiCL) and deep silt loam (SiL) or loam (L) soil in 2013, 2014, and 2015. Irrigation was initiated at multiple times and soybean yield and net return were determined. Growth stage, soil water potential (SWP), and soil water deficit (SWD) were compared at these initiation timings to determine which parameter or combination of parameters consistently predicted the resulting greatest yields and net returns. Stress conditions that reduce yield can occur at any time from late vegetative stages to full seed on these deep soils. The wide range of trigger values found for SWP and SWD to increase yields in different years indicates that monitoring soil moisture by itself or use of a single trigger value may not be sufficient to optimize irrigation scheduling to maximize soybean yield with the least amount of water every year on these soils. Other parameters (ex: leaf water potential, canopy temperature, air temperature, humidity, solar radiation, and wind) may need to be monitored in conjunction with soil moisture to directly or indirectly quantify the abiotic stresses on the plant to better define when a yield reducing stress is occurring.