Silage Fermentation and In Vitro Degradation Characteristics of Orchardgrass and Alfalfa Intercrop Mixtures as Influenced by Forage Ratios and Nitrogen Fertilizing Levels

Intercropping is a globally accepted method of forage production and its effect on silage quality depends not only on forage combination but also fertilization strategy. In the present study, field intercropping of orchardgrass (Dactylis glomerata) and alfalfa (Medicago sativa) at five seed ratios (100:0, 75:25: 50:50, 25:75, 0:100 in %, based on seed weight) was applied under three N fertilizing levels (0, 50, and 100 kg/ha), and harvested for silage making and in vitro rumen degradation. As a result of intercropping, the actual proportions (based on dry matter) of alfalfa in mixtures were much closer to seed proportion of alfalfa in field, except 75:25 orchardgrass-alfalfa intercrops with no fertilization. The actual proportions of alfalfa in mixtures decreased by 3–13% with the increase of N level. Increases of alfalfa proportion in mixtures increased silage quality, nutrients degradability and CH4 emissions. Increasing N levels increased silage pH, concentration of butyric acid, and fiber fractions. In summary, inclusion of alfalfa at around 50% in orchardgrass-alfalfa silage mixtures were selected for favorable ensiling and higher forage use efficiency while also limiting CH4 emissions, compared to monocultures. The silage quality and feeding values of mixtures were influenced more by forage ratios than by N levels.