Drainage and Subirrigation of Soybean In Northeast Missouri.

Integrated water management systems using drainage plus subirrigation (DSI) have reduced nitrate-loading of drainage water flow and may increase soybean yield. Shallow drain tile depths and narrow spacings are recommended for claypan soils. Field research (2003 to 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 non-drained (ND) and non-drained 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 non-drained control due to poor drainage in three of the four years. 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 to 910 kg ha^-1) while DO at the same spacings increased yield 9 to 22% (300 to 710 kg ha^-1) compared to ND or NDDP controls. In a dry year (2005), drainage plus subirrigation increased yield up to 1,200 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 four years was lower with DSI compared with DO or ND controls, which was affected by the spring-summer precipitation regimes.