Yield and Silage Quality of Winter Legume Cover Crop Mixtures Without Nitrogen Fertilization in Spring

A field experiment was conducted in two seasons (2019-2020 and 2020-2021) at three locations in Slovenia (Rogoza, Fala, and Brežice) to evaluate the yield and silage quality of winter cover crops (WCCs). The experiment included Italian ryegrass (IR) in pure stands, fertilized with nitrogen in spring, and mixtures of crimson clover (CRC), red clover (RC), and IR+CRC+RC without nitrogen fertilization in spring. The highest dry matter yield (DMY) was observed in IR+CRC+RC (4.98 t ha^-1). For fresh feed, the CRC+RC treatment had significantly higher (p < 0.05) crude protein (208 g kg^-1 DM), nitrate nitrogen (116.7 mg kg^-1 DM), and buffering capacity (1290 mmol kg^-1 DM) but significantly lower (p < 0.05) dry matter (128 g kg^-1) and water-soluble carbohydrates (121 g kg^-1 DM). For silage, the CRC+RC treatment had significantly lower (p < 0.05) dry matter (476 g kg^-1 silage), metabolic energy (9.65 MJ kg^-1 DM), net energy of lactation (5.77 MJ kg^-1 DM), and neutral detergent fiber (375 g kg^-1 DM) but higher ammonia nitrogen (66.5 g kg^-1 of total nitrogen), crude protein (158 g kg^-1 DM), and acid detergent fiber (279 g kg^-1 DM). No significant differences (p > 0.05) were found among treatments for acetic, lactic, and butyric acid, crude fat, pH, and soil mineral nitrogen (N_min). The results of the study show that the same or higher DMY and a comparable quality of highly wilted silage can be produced with mixed Italian ryegrass and clovers compared with those of Italian ryegrass in pure stands. The experiment aimed to determine whether clover-based mixtures can achieve comparable silage quality and dry matter yield without spring N fertilizers compared with those of pure stands of Italian ryegrass fertilized in spring.