Forage Mass and Nutritive Value of Grain- and Forage-Type Soybean Cultivars Managed under Different Row Spacings and Clipping Heights

Abstract

Soybean (Glycine max L.) is a high value crop that has been used as a forage since the early 1900s in the southern U.S. (e.g., Mississippi, Alabama, Georgia, South Carolina, and Florida). Renewed interest has increased the use of soybean as a viable and economical high protein alternative to forage growers in the southern region. The objective of this study was to determine herbage mass (HM) and nutritive value of forage soybean managed under two row spacing (36 and 72 cm) and three stubble heights (10, 15, and 20 cm). Five cultivars were used ‘Stonewall’, ‘Laredo’, ‘Tower of Leaves’, Asgrow® ‘AG64X8’, and Asgrow® ‘AG79X9’ and sown at two locations (Shorter and Headland, AL). Forage was harvested in July and August during both years and HM was determined. Crude protein (CP) and fiber fractions were determined using near-infrared spectroscopy. Years and location did vary, but overall, Stonewall had the greatest (p < 0.026) HM (1706 kg DM ha−1) with a high nutritive value (124 g CP kg−1, 449 g NDF kg−1, and 372 g ADF kg−1). Laredo had the lowest HM (1169 kg DM ha−1; p < 0.025). The 10 cm stubble height resulted in increased HM (1898 kg DM ha−1; p < 0.0001) but decreased nutritive value (149 g CP kg−1; 331 g ADF kg−1; 413 g NDF kg−1; p = 0.001) compared to 20 cm (179, 282, and 375 g kg−1 for CP, ADF, and NDF, respectively). Row spacing did not consistently influence either HM or nutritive values. Due to its relatively good nutritive value and HM, forage soybean should be considered as a monoculture or in a mixed sward with other warm-season annual forages for inclusion in forage-based livestock diets.