Fermentation of Cowpea Alone or in Mixture with Corn or Forage Sorghum for Silage.

Addition of legumes to cereals may improve nutritive value of the resultant silage. The objective of this study was to assess the fermentation characteristics of cowpea (Vigna unguiculata L. Walp.) when in mixture with corn or forage sorghum for silage. Cowpea  (CB), corn (CS), and forage sorghum (FS) were grown in separate fields at the NMSU-Agricultural Science Center, Clovis, NM in 2009. All three crops were grown under irrigated conditions and were fertilized based on soil nutrient analysis. Corn, forage sorghum, and cowpea were harvested at half-milk line, late-dough stage, and vegetative stage respectively. Crops were chopped separately at a theoretical length of 20 mm. Approximately 20 kg of each chopped crop was taken to the lab for ensiling. Six CS/FS-CB combinations were developed, three for CS-CB and three for FS-CB, 1) 25-75, 2) 50-50, 3) 75-25, 4) 100% CB, 5) 100% CS, 6) 100% FS. A 500-g sample of each combination was vacuum sealed in a plastic bag with four bags per treatment. Mixtures were fermented for 137 d at room temperature (25^oC). Silages were analyzed for fiber and fermentation characteristics. Comparing to CS and FS alone, on average CS-CB and FS-CB mixtures increased crude protein (CP) from 26 to 102 g kg^-1 DM as the proportion of CB increased from 25% to 75%. Mixing CB with FS increased digestibility, NDF digestibility, and energy; however, mixing with CS resulted in the opposite effect. Cowpea in mixture with either CS or FS had a more heterolactic fermentation than CS or FS alone. The pH, lactic and acetic acids increased as CB increased in the mixture. The CB alone silage had high pH (5.93), very low lactic acid (0.9 g kg^-1 DM) and high butyric acid (4%). Cowpea bean in mixture with FS presents a better option than in mixture with CS.