Corn growth and yield response to subsurface drain spacing on clermont silt loam soil

Subsurface drainage is an important water management practice on naturally poorly drained soils, and recommendations for appropriate drain spacings for particular soils continue to evolve. The objective of this long-term study was to measure corn (Zea mays L.) growth and yield as affected by subsurface drain spacing on a soil that was traditionally not tile drained. Three drain spacings (5, 10, and 20 m) were compared with a nondrained "control" (40 m) for plant population, grain yield, and moisture content over a 10-yr period on a low-organic-matter silt loam soil. In addition, corn populations, heights at 4 and 8 wk, yield, and moisture were measured with distance from the drain for the 5-,10-, and 20-m spacings. Significant distance effects occurred more frequently for the 20-m spacing than for the 10- and 5-m spacings, especially for grain yield and moisture. The 10-yr average corn yields were 9.8, 9.7, 9.5, and 9.2 Mg ha(-1) for the 5-,10-, and 20-m plots and the nondrained control plots, respectively. Grain yield was 1.3 to 1.7 Mg ha(-1) lower in the nondrained control than in the 5-m spacing in 3 of the 10 yr and was likely due to both planting date delays and wetter soil conditions after planting. The smaller-than-expected yield differences among treatments may reflect the excellent surface drainage in this field as well as optimal planting dates in 7 of the 10 years. The results demonstrate that drainage improvements are a long-term investment and may not provide yield benefit in every year.