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Scheduling of Furrow Irrigation Initiation on Soybean Yield and Net Returns

The majority of soybeans (Glycine max L. Merr.) grown in alluvial soils of the Mid-South USA are irrigated. The impact of delayed irrigation initiation of 0, 5, 10, and 15 days on soybean growth, yield, and economic returns was investigated for three seasons on two contrasting soils located 1,000-ft distance apart: silt loam and silty clay. Scheduling was determined using the Arkansas Scheduler, a deficit-driven program. On the silt loam soil, cultivars representing maturity groups (MG) 3, 4, and 5 were planted in 2007, 2009, and 2010. In 2007, delays of 15 days were omitted on the silt loam soil due to rain. On the silty clay, MG 4 was planted in 2008 and MG 5 in 2009 and 2010. Delays of 15 days reduced seed yields and net returns in 2 of 3 years on the silt loam for MG 3 and 4 cultivars but not for MG 5. On the silty clay, a 15-day delay reduced yields in all three seasons but had no effect on net returns. Irrigation initiation delays reduced plant heights and canopy cover at both sites and all seasons, especially for 15-day delays. Delays in irrigation initiation of 15 days increased risk for early maturing indeterminate cultivars more than later-maturing determinate cultivars in the silt loam soil and for all cultivars in the silty clay. However, delaying irrigation initiation by as much as 10 days for determinate cultivars can potentially reduce irrigation costs without sacrificing yield and net returns. S (Glycine max L. Merr) are the most common crop species grown on alluvial soils of the Mid-South USA. Increasingly, more of the production fields are irrigated using alluvial aquifer groundwater, and in most regions, unfortunately, the withdrawal of alluvial aquifer groundwater is occurring at unsustainable levels (Czarnecki et al., 2002). A critical groundwater shortage with devastating effects on the economic vitality of the region may result unless more sustainable methods of irrigation management occur. Irrigation of crops generally increases yield, improves yield uniformity, and reduces economic risk for the producer (Wesley et al., 1991). Efficient scheduling of irrigation events necessitates re-supply of soil moisture prior to crop extraction capabilities that would result in irreversible yield losses. Several methods of scheduling irrigation have been used such as deficit irrigation, simulation models (Cahoon et al., 1990; Payero et al., 2005), weather data– driven estimates of potential evapotranspiration (Ortega-Farias et al., 2004), soil moisture sensors (Leib et al., 2003; Bryant et al., 2017), atmometers (Gleason et al., 2013), and canopy temperature monitoring (Stockle and Dugas, 1992; Bockhold et al., 2011). Crop Forage Turfgrass Manage. 4:180033. doi:10.2134/cftm2018.05.0033 © 2018 American Society of Agronomy and Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711 All rights reserved. Published October 25, 2018