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-greeen manure)-corn; ii) wheat (Red clover [RC, Trifolium pratense L. ‘medium’] eariy-kill)-corn (cv. Pioneer 3751); and (iii) wheat (RC late-kill)-corn. Soil type was Kilmanagh loam (fine-loamy, mixed, nonica, mesic Aerie 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. Research QuestionLegume green manures can benefit subsequent grain crops through both the contribution of biologically fixed N and rotation effects. However, when water is limiting, legume green manures can have a negative effect on subsequent crops. Our main objective was to determine the effect early kill of a legume green manure had upon soil water content, N contribution, and the grain and N yield of a following corn crop in both nonirrigated and subirrigated systems. The net revenue provided by each of the cropping systems was calculated. Literature SummaryThe significant quantity of N that can be accumulated by legume green manures is a major reason for including them in cropping systems. In order to increase the quantity of N accumulated, green manures may be allowed to grow until the time of planting a subsequent crop. However, under water limiting conditions, depletion of soil water by a living green manure may reduce emergence, limit early growth, and reduce grain yield of a subsequent crop. To avoid soil water depletion, several researchers suggest killing a green manure 2 to 3 wk prior to planting a subsequent crop. However, little research has been reported on the effect early kill may have on soil water contents, N contribution, or the performance of the subsequent crop. Study DescriptionThis research was conducted in Huron County, Michigan, on a Kilmanagh loam. Two parallel experiments were performed, one experiment was subirrigated, the other was not irrigated. During 1993 and 1994 three 2-yr cropping systems were investigated: (i) wheat (no-green manure)-corn; (ii) wheat (RC earlykill)-corn; and (iii) wheat (RC late-kill)-corn. RC = red clover green manure; early-kill = RC killed approximately 2 wk prior to planting corn, and late kill = RC killed 3 d prior to planting corn. Red clover was killed by application of Roundup either 2 wk prior to corn planting or by plowing at the time of corn planting the year following red clover establishment. The corn in each of these systems was fertilized with ammonium nitrate fertilizer rates of 0, 62, 125, and 187 lb N/acre. Yield and N content of wheat, red clover, and corn were measured each year. Total season rainfall (May–September) was 14 in. in 1993 and 18 in. in 1994. Applied QuestionsDid early kill of red clover reduce the quantity of red clover N and biomass contributed to the cropping system? How did this reduced contribution affect the yield and economic return of a subsequent corn crop? A 2 wk difference in the time of killing a red clover green manure resulted in less N (50 and 28 lb N/acre in 1993 and 1994, respectively, averaged across irrigation) and biomass (1600 and 530 lb/acre in 1993 and 1994, respectively, averaged across imgation) being contributed but did not affect grain yield or N content of a following corn crop in either 1993 or 1994. The red clover systems, regardless of time of kill, produced corn grain yields higher than grain yields in the no green manure system (Fig. 1). Because of higher grain yields and reduced necessity of fertilizer N, the red clover systems had economic returns that were higher or equal to the economic returns from the no-green manure systems. Was soil water content affected by time of killing the red clover? At the time of corn planting in 1993, but not 1994, soil water content was higher in the early-kill RC system than in the late-kill RC or no-green manure systems. However, these differences did not remain throughout the growing season. Did subirrigation increase yield or revenue of either the no-cover or RC cropping systems? Subirrigation resulted in lower corn yields when no fertilizer was applied to the no-cover systems. However, subirrigation did not affect corn yields at higher N rates in the no-cover system or in the RC system. Due to expenses associated with installing and operating the subirrigation system, net revenue tended to be lower in the subirrigation than in the nonirrigated system. RecommendationRed clover based N systems produced higher yields and revenue than fertilizer based N systems in both nonimgated and subirrigated systems. Therefore, we recommend wider use of RC green manure in cropping systems. We also recommend that during years when growers are concerned with legume green manure induced water deficits that green manures be killed at least 2 wk prior to planting a subsequent crop. This can be done without compromising the benefit associated with the legume. Fig. 1Effect of fertilizer N and cropping system (no green manure, early-kill red clover, and late-kill red clover) on corn grain yields. Grain yields are averaged across years and the subirrigated and nonirrigated experiments.