Effect of nitrogen application on the production performance and soil nutrients of cultivated Leymus chinensis grassland in the Songnen Plain

To clarify the effect of nitrogen application on the production performance and soil nutrients of cultivated Leymus chinensis grassland, this study used the cultivated L. chinensis grassland as the research subject. A randomized block design was employed with different nitrogen treatments: N₀ (0 kg·ha⁻¹), N₁ (42 kg·ha⁻¹), N₂ (84 kg·ha⁻¹), and N₃ (126 kg·ha⁻¹). Through two consecutive years of experimentation and observation in 2018 and 2019, the plant height and dry matter yield of cultivated L. chinensis grassland as well as soil pH, soil organic matter, total nitrogen, available nitrogen, total phosphorus, and available phosphorus under different nitrogen application levels were analyzed. The results showed that the plant height and dry matter yield of L. chinensis initially increased and then decreased with increasing nitrogen application, with the best performance being observed at the nitrogen application rate of 84 kg·ha⁻¹ (N₂ treatment), which was followed by a declining trend. In 2018 and 2019, compared with that in the N₀ (control), the dry matter yield of L. chinensis under N₂ treatment increased by 43.20% (P < 0.05) and 22.15%, respectively. N₂ treatment also significantly increased the total nitrogen and total phosphorus content in the 0－10 cm soil layer in 2019 but had no significant effect on the soil pH. Correlation analysis indicated that the plant height and dry matter yield of L. chinensis significantly positively correlated with soil organic matter content, soil total phosphorus, and available phosphorus (P < 0.05), and significantly negatively correlated with soil pH (P < 0.01). In summary, the optimal nitrogen fertilizer application rate for improving the production and soil fertility of cultivated L. chinensis grassland in the Songnen Plain was found to be 84 kg·ha⁻¹.