Fertility and Weed Stress Effects on Performance of Maize/Soybean Intercrop

Intercropped corn (Zeu mays L.) and soybean [Glycine mux (L.) Merr.] may produce more total yield per hectare than either grown separately, ie., land equivalent ratio (LER) >l. Low N fertility, limited moisture, and weed competition have each been reported to result in high land equivalent ratios. Thus it was hypothesized that intercropping advantages were greater under stress conditions. The objectives were to study the effects of soil fertility stress (F, = low N-P-K, F2 = high N-P-K), weed competition stress (W, = unweeded, W2 weeded), and four cropping systems (M2S, MIS, M2, S; where M, = high density maize, M, = low density maize, and S = soybean at normal density) on the performance of maize and soybean, and on the growth of weeds. ‘Cargill 921’ maize and ‘Union’ soybean were planted simultaneously in 1985 and 1986 in alternate rows spaced at 0.5 m on a typic Hapludult in Maryland. Land equivalent ratios and maize equivalent yields were calculated. Dry matter production was determined early in the season, and grain yield plus weed dry matter were determined at final harvest. LER values (mean of 1985 and 1986) ranged from 0.89 (W,F,M2S) to 1.18 (W2FIMIS). The LER data showed that at high fertility levels, weed stress increased the relative advantage of intercropping. In addition, when plots were weeded, LER increased from 0.96 to 1.13 under fertility stress. Maize equivalent yields were calculated from the relative prices of maize and soybeans. The highest maize equivalent yields in all cropping systems in both years occurred under optimal con-