Response of corn grain yield to early and late killed red clover green manure and subirrigation

Killing a legume green manure weeks before planting a subsequent grain crop may prevent legume induced water deficits that can be detrimental to a subsequent crop. However, little research has been reported on the effect this strategy has upon a subsequent grain crop. This field study was conducted to determine the effect of time of killing a legume green manure on the yield and N uptake of a subsequent corn (Zea mays L.) crop in subirrigated (SI) and nonirrigated (NI systems. Three 2-yr cropping systems were studied: (i) wheat (Triticum aestivium L. var. Frankenmuth) (no-green manure)-corn; ii) wheat (Red clover [RC, Trifolium pratense L. 'medium'] early-kill)-corn (cv. Pioneer 3751); and (iii) wheat (RC late-kill)-corn. Soil type was Kilmanagh loam (fine-loamy, mixed nonica, mesic Aeric Haplaquepts). Red clover was established by interseeding into wheat. Red clover was killed either 2 wk (early-kill) or several days (late-kill) prior to planting corn the spring following the year of establishment. Early-kill RC accumulated less N than late-kill RC (50 and 28 lb N/acre in 1993 and 1994, respectively, averaged across irrigation). However, time of kill did not significantly affect ear-leaf N content, grain, or N yield of the following corn crop. Grain yield of corn following red clover with no N fertilizer applied was similar to grain yield with no green manure and 125 lb N/acre (1993) or 187 lb N/acre (1994) applied. Soil water contents were higher in the early- than late-kill RC systems at the time of corn planting in 1993. Subirrigation did not significantly affect corn grain yield in either year. The legume based cropping systems were equally or more profitable than the no green manure system. Results indicate that (i) corn planting should not be delayed in order to allow a green manure to accumulate N or biomass and (ii) killing RC early may be effective for limiting soil water depletion in spring without sacrificing benefits to a following grain crop.