Soybean Response to Drainage and Subirrigation on a Claypan Soil in Northeast Missouri

Integrated water management systems using drainage plus subirrigation (DSI) have reduced nitrate-loading of drainage water flow and may increase soybean [Glycine max (L.) Merr.] yield. Shallow drain tile depths and narrow spacings are recommended for claypan soils. Field research (2003-2006) evaluated the effects of drainage (DO) and DSI on planting date and the effects of DO and DSI at 6.1 and 12.2 m spacings on soybean yield compared to nondrained (ND) and nondrained delayed planting (NDDP) controls on claypan soils. Soybean were planted up to 17 d earlier with DO or DSI systems. Plant populations were reduced 29 to 52% in the nondrained control due to poor drainage in 3 of the 4 yr. Grain yield, water applied through the DSI system, and water level depth were similar at a 6.1 or 12.2 m drain tile spacing. Average yield increase with DSI at 6.1 and 12.2 m spacings was 12 to 29% (410-910 kg ha(-1)) while DO at the same spacings increased yield 9 to 22% (300-710 kg ha(-1)) compared to ND or NDDP controls. In a dry year (2005), drainage plus subirrigation increased yield up to 1200 kg ha(-1) compared to DO. Plant population variability at harvest was lower with the DO or DSI systems compared to ND or NDDP controls. Yield variability over the 4 yr was lower with DSI compared with DO or ND controls, which was affected by the spring-summer precipitation regimes and is important to farmers for a more predictable soybean marketing strategy.