Subsurface Drain Tile Spacing Affects Yield Variability of Corn in a Claypan Soil.

Poorly drained claypan soils are common in the Midwestern United States. Subsurface tile drainage systems used in conjunction with water-level control structures for subirrigation have increased Zea mays L. grain yields in Northeast Missouri. Analysis of 42 year-hybrid-nitrogen management systems from 2002 to 2015 near Bethel, Missouri evaluated 6.1 and 12.2 m drainage tile spacings (DO) and drainage tile spacings with sub-irrigation (DSI). Yields, plant populations, and moisture content were determined at 3.05 m intervals above and between the 6.1 and 12.2 m spaced subsurface tile lines, and were compared to non-drained (ND) and non-drained delayed planting (NDDP) controls. For all data, average grain yields increased 27% (2,010 kg/ha) with DO at a 6.1 m spacing compared to the non-drained controlled. DSI at a 6.1 m spacing increased yields 38% (2,770 kg/ha) compared the non-drained control. Yields were evaluated by low (<6,290 kg/ha), low-medium (6,290-9,430 kg/ha), medium-high (9,430-12,580 kg/ha), and high (>12,580 kg/ha) yield sites to better understand variability among systems and spacings. In a low yield environment, yields above a 6.1 m spaced tile line were 74% greater than between the tile line, while yields above the tile lines were three times greater than the ND control. Grain yield variability generally decreased from a low-medium yielding to a high yielding environment. Narrower drain tile spacings may need to be installed to reduce grain yield variability in low to medium yielding environments, but cost of installation will increase and the return on investment needs to be determined.