Sorghum intercropping effects on yield, morphology, and quality of forage soybean

Shading patterns when two forage species are intercropped may be different than in a monocrop environment. Our objectives were to quantify yield and forage quality response of forage soybean [Glycine max (L.) Merr.] intercropped with forage sorghum [Sorghum bicolor (L.) Moench] and compare to the measurements of monocrop soybean. Soybean plants were harvested from the middle portion of individual rows in plots containing only soybean and from plots having alternating soybean and sorghum rows spaced 76 cm apart. Morphological and forage quality measurements were determined on leaf and stem fractions. Morphological measurements included main stem length, node number, leaf area ratio (LAR), specific leaf weight (SLW), and stem diameter. Forage quality constituents included in vitro dry matter disappearance (IVDMD), neutral detergent fiber (NDF), hemicellulose, and cellulose, and crude protein (CP) concentrations. Intercropped soybean had 6 more plants m^-1 of row, less advanced morphological development, and 2.3 Mg ha^-1 less dry matter than monocrop soybean. Leaf IVDMD, NDF, hemicellulose, and cellulose did not differ between intercrop and monocrop soybean. However, stem IVDMD was 33 g kg^-1 greater for intercropped than monocrop soybean, reflecting the 36 g kg^-1 decrease in NDF concentration. Intercropped soybean was lodged both years more than monocrop soybean, which may have been due to the significant decrease in stem NDF. Leaf CP concentration was 25 g kg^-1 greater for monocrop soybean than intercropped soybean; however, stems from intercropped soybean had 12 g kg^-1 greater CP than monocrop soybean stems. Soybean exhibited a high degree of morphological plasticity, presumably in response to increased competition for solar radiation. Although forage quality of intercrop soybean was greater than monocrop soybean, intercropping forage-type soybean with another tall-growing forage does not appear to be practical because of the decrease in dry matter accumulation.