Dietary Nutritive Value, Dung Quality, Decomposition, and Nutrient Movement into Soil in Smooth Bromegrass Pastures

Legumes increase forage nutritive value in pastures; however, literature addressing the impacts on dietary nutritive value, dung quality, decomposition, and nutrient movement into soil remains scarce. Cattle grazing legume-interseeded smooth bromegrass (Bromus inermis Leyss.) pastures may select diets with greater nutritive value and consequently produce dung that decomposes faster and increases nutrient movement into soil relative to cattle grazing N-fertilized and unfertilized smooth bromegrass pastures. In 2014 and 2015, we collected rumen and dung samples from replicated experiments to evaluate effects of season (June and August), pasture type (legume-interseeded, N-fertilized, and unfertilized pastures), and harvest time (3, 7, and 30 d after deposition) on dietary nutritive value, dung quality, dung decomposition, and nutrient movement into soil. Cattle grazing legume-interseeded pastures had similar dietary crude protein concentrations but 11% less dietary neutral detergent fiber concentrations than cattle grazing N-fertilized pastures. Dung from cattle grazing legume-interseeded pastures, meanwhile, had 5 to 12% greater N concentrations than dung from cattle grazing N-fertilized and unfertilized pastures. From 3 to 30 d after deposition, dung C/N ratio decreased from 20.0 to 16.5; whereas, dry matter remaining diminished to 77.5%. Dung C/N ratio and dry matter remaining did not vary with season or pasture type. At Day 7, soil below dung from cattle grazing legume-interseeded pastures had 20 and 42% greater inorganic N than soil below dung from N-fertilized and unfertilized pastures. This research showed that pastures with legumes increases dietary nutritive value, resulting in greater dung quality and increased N movement into soil.