DRY-MATTER PARTITIONING AND FORAGE NUTRITIVE-VALUE OF SOYBEAN PLANT-COMPONENTS

Soybean [Glycine mar (L.) Merr.] can be a high-quality alternative for age, but little is known about the influence of management practices o n partitioning and composition of soybean plant components, and theref ore on whole-plant forage quality. Cultivar, row spacing, planting rat e, and harvest maturity effects on the dry matter partitioning and nut ritive value of soybean plant parts were determined in a 2-yr field st udy. The cultivars Corsoy 79, Pella, and Williams 82 were grown in 20- and 76-cm row spacings at planting rates of 280 000 and 890 000 seeds ha-1. Plants were harvested at R1, R3, R5, and R7 stages of developme nt. Harvest maturity had the greatest effect on dry matter partitionin g and nutritive value of soybean plant parts. The leaf dry matter frac tion decreased continually as plants were harvested at later reproduct ive growth stages, declining from 708 g kg-1 at R1 to 168 g kg-1 at R7 . The stem fraction of total plant mass increased from 292 g kg-1 at R 1 to 383 g kg-1 at R5 and then declined to 283 g kg-1 at R7. The pod f raction increased from 105 g kg-1 at R5 to 549 g kg-1 at R7. As plants matured, neutral-detergent fiber (NDF), acid-detergent fiber (ADF), a nd acid-detergent lignin (ADL) concentrations increased; crude protein (CP) concentration decreased for leaf and stem components. The greate st change occurred as plants matured from Stage R5 to R7. The pod comp onent showed an opposite trend, with NDF, ADF, and ADL concentrations decreasing and CP concentration increasing between Stages R5 and R7. R ow spacing, planting rate, and cultivar had little effect on dry matte r partitioning and nutritive value of soybean plant parts.