Comparative study on soil carbon and nitrogen contents and mineralization in different mixed grassland

To investigate the effects of different grass species combinations on soil carbon and nitrogen dynamics, we conducted a completely randomized design experiment with three single sowing patterns (Medicago sativa; Bromus inermis; Elymus nutans) and four mixed sowing patterns (Medicago sativa+Bromus inermis; Medicago sativa+Elymus nutans; Bromus inermis+Elymus nutans; Medicago sativa+Bromus inermis+Elymus nutans). The contents of soil total nitrogen, nitrate nitrogen, ammonium nitrogen, and organic matter were monitored over four consecutive years, carbon and nitrogen mineralization rates and cumulative mineralization were measured in the fourth year. The results showed that the contents of soil total nitrogen, nitrate nitrogen, ammonium nitrogen, and organic matter content in the Medicago sativa+Bromus inermis+Elymus nutans mixed sowing pattern were significantly higher than those in other mixed and single sowing patterns. In Medicago sativa+Bromus inermis+Elymus nutans and Medicago sativa+Bromus inermis sowing combinations, mineralization rates were significantly higher than those in other sowing patterns throughout the study period, while the amounts of cumulative mineralization exceeded those in single sowing patterns. Therefore, the mixed sowing patterns Medicago sativa+Bromus inermis and Medicago sativa+Bromus inermis+Elymus nutans enhance soil carbon and nitrogen storage and promote nutrient transformation, which can be used as an optimized planting model of artificial grassland.