Growth stage scheduling criteria for sprinkler-irrigated soybeans

Abstract

Soybean [Glycine max (L.) Merr.] producers in the Great Plains region usually employ either a seasonal soil water balance approach, or a growth stage sensitivity approach, relative to scheduling sprinkler irrigation events. We conducted an empirical evaluation of the response of six soybean cultivars to three irrigation strategies. One was an irrigation scheduling (IS) system based solely on maintaining a soil water content in the root zone between 50% and 80% of the total plant available soil water capacity. The other two strategies involved the same depletion criterion for triggering irrigation events, except that the first irrigation was intentionally delayed until the flowering (FL) stage, or the mid-pod elongation (PD) stage. The total water amount applied during each season was approximately similar for the IS, FL, and PD strategies. Thus, the primary difference among the three strategies was the time frame during which irrigation events were scheduled. In the 1983 test, the yields attained in the IS, FL, and PD treatments were not significantly different from each other (i.e. 4.08, 4.08, and 4.04 Mg/ha, respectively), and were nearly double the yield obtained in the nonirrigated (NI) check treatment (2.29 Mg/ha). In the 1984 test, the yields of the IS, FL, and PD treatments were again not significantly different (2.02, 2.05, and 2.22 Mg/ha, respectively). However, the 1984 yield response to irrigation was also not significant relative to the NI check (1.90 Mg/ha), primarily because of low plant populations and a shorter growing season. Thus, this two-year experiment indicated that delaying irrigation until the FL or the PD stages of soybean reproductive development could be just as effective (i.e. 1983 data), or at least no more ineffective (i.e. 1984 data), in enhancing soybean yield compared to the IS strategy (Fig. 1). The soil water balance and soybean growth stage sensitivity approaches, when combined, could thus constitute an effective strategy of soybean sprinkler irrigation management in the Great Plains region.