Effects of Intercropping, Nitrogen Fertilization and Corn Plant Density on Yield, Crude Protein Accumulation and Ensiling Characteristics of Silage Corn Interseeded into Alfalfa Stand

Interseeding silage corn into an alfalfa stand following its spring harvests to produce mixed silage would feasibly break the restriction of alfalfa production during a hot-rainy summer. In this 2-yr experiment, the alfalfa–silage corn intercropping system (AC) with nitrogen (N) fertilization rates of 0, 60, 120, and 180 kg N ha−1 and corn plant densities of 30,000, 45,000, and 60,000 plants ha−1 was compared with the monocultured corn (CK) managed using the local farmers’ practice. Intercropping with alfalfa significantly decreased the dry matter (DM) yield of the corn by 31.5% on average, while increasing the N application rate and corn plant density promoted DM yield and crude protein (CP) accumulation of the intercropped corn, and the intercropping system could achieve the same CP yield as CK—it did in most cases. Although the DM contents, pH values, and NH3-N concentrations were decreased in the mixed silage, its fermentation quality was not reduced and the CP, water soluble carbohydrates, and lactic acid contents were dramatically increased by 16.3%, 17.8%, and 72.9% compared with those of CK, respectively. For the opposite effects of N fertilization and corn density on silage quality, the treatment combination with a medium corn density (45,000 plants ha−1) fertilized at a medium N rate (120 kg N ha−1) was evaluated as the optimum for more balanced system productivity, silage nutritive values and fermentative characteristics during the coexisting period.