The effect of soybean variety on corn-soybean intercrop biomass and protein yields

Soybean intercropped with corn can produce a high-quality silage, but pods of early maturing soybean varieties usually shatter when harvested, thus reducing the silage protein potential. In 1991 and 1992, an experiment was conducted in Truro, Nova Scotia, and Sussex, New Brunswick, to determine whether later soybean varieties can provide sufficient biomass and protein in intercrops and escape pod losses at harvest. Early, early high protein, medium, late and very late maturing varieties of soybean were grown as monocrops and intercrops with corn. Eight response variables were measured: soybean shoot biomass yield, intercrop shoot biomass yield, soybean shoot protein concentration, intercrop shoot protein concentration, soybean shoot protein yield, intercrop shoot protein yield, soybean seed biomass yield and soybean seed protein concentration. The two later soybean varieties had higher yields than the two early varieties, contributing to higher protein yields in the later varieties than in the early varieties, under both monocropping and intercropping. In contrast to the corn monocrop, intercrops with all soybean varieties produced higher protein concentrations. Under intercropping, only the late variety produced significantly higher protein yields than the corn monocrop; however, none of the varieties resulted in significantly lower biomass yields than the corn monocrop. With the late soybean variety, land equivalent ratios of the intercrop shoot biomass yield and the intercrop shoot protein yield revealed yield advantages of intercrops over monocrops of 21% and 10%, respectively. The late variety resulted in an increased intercrop shoot protein concentration without reducing the intercrop shoot biomass yield, because it was still green enough to be harvested with minimal pod shattering.