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 detrimenta l 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 legum e green manure on the yield and N uptake of a subsequent corn (Zea may s L.) crop in subirrigated (SI) and nonirrigated (NI) systems. Three 2 -yr cropping systems were studied: (i) wheat (Triticum aestivium L. va r, Frankenmuth) (no-greeen manure)-corn; ii) wheat (Red clover [RC, Tr ifolium pratense L. 'medium'] early-kill)-corn (cv, Pioneer 3751); and (iii) wheat (RC late-kill)-corn, Soil type was Kilmanagh loam (fine-l oamy, mixed, nonica, mesic Aeric Haplaquepts), Red clover was establis hed by interseeding into wheat. Red clover was killed either 2 wk (ear ly-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 significa ntly affect ear-leaf N content, grain, or N yield of the following cor n 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/a cre (1993) or 187 lb N/acre (1994) applied, Soil water contents were h igher in the early-than late-kill RC systems at the time of corn plant ing in 1993, Subirrigation did not significantly affect corn grain yie ld in either year. The legume based cropping systems were equally or m ore profitable than the no green manure system. Results indicate that (i) corn planting should not be delayed in order to allow a green manu re to accumulate N or biomass and (ii) killing RC early may be effecti ve for limiting soil water depletion in spring without sacrificing ben efits to a following grain crop.