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.