Yield, digestibility, and nutritive value of crabgrass as impacted by nitrogen fertilization rate and source

Crabgrass (Digitaria spp.), a summer annual grass capable of self reseeding, could provide high quality grazing, but little is known about its management in the mid-Atlantic region. This study evaluated the effects of N fertilizer rates and sources on crabgrass yield and nutritive value. Plots were established in late spring of 2001-2003 near Blackstone, VA. The experimental design was a randomized complete block with a factorial treatment arrangement and four replications. Nitrogen rates ranging from 0 to 336 kg ha^-1 were applied in 56-kg intervals at seeding as ammonium nitrate (NH ₄NO₃) or broiler litter. Plots were harvested twice in 2001 and three times in 2002 and 2003. Yield increased with N rate for all harvests. Over years and N sources, seasonal yield ranged from 4.2 to 9.8 Mg ha^-1. Maximum yield occurred at 300 kg N ha^-1. Nitrogen source had little effect on yield but dramatically impacted forage nitrate levels. Over years and N sources mean in vitro true digestibility (IVTD) for first, second, and final harvests were 880, 871, and 786 g kg^-1. In 2001 and 2003, first harvest IVTD was negatively correlated with N rate, but positively related at second harvest. Nitrogen source had little effect on IVTD. Over years, N rates, and N sources, CP concentrations at first, second, and final harvests were 105, 105, and 76 g kg^-1. These data indicate that crabgrass is a productive and nutritious forage, and that readily available organic N sources such as broiler litter could be effectively utilized for its production.