Effects of irrigation and nitrogen management on yield and physiological characteristics of Italian ryegrass

Breeding lands contain large amount of left over fertilizer, which can still be utilized by plants. To investigate the effect of irrigation and nitrogen management on yield and physiological characteristics of Italian ryegrass (Lolium multiflorum) in such breeding land, four irrigation amount (0, 1 200, 1 800, and 2 400 m³·hm⁻²) and four nitrogen application rate (0, 160, 240, and 320 kg·hm⁻²) treatments were used. The results showed that 1800 m³·hm⁻² irrigation amount resulted in the highest dry matter yield. Fresh matter yield of 0 m³·hm⁻² nitrogen application rate was significantly lower than that of 240 or 320 m³·hm⁻² (P < 0.05). However, there was no significant difference between the fresh matter yield of 160 kg·hm⁻² nitrogen application rate and the other three nitrogen application rates. The net photosynthetic rate (Pn) of Italian ryegrass showed an N-shaped trend with increasing irrigation amount, and the irrigation amount had a significant effect on the Pn and transpiration rate (Tr) (P < 0.05). Nitrogen application rates did not significantly affect the indicators of photosynthetic characteristics except Pn. As the irrigation amounts increased, the proline and malondialdehyde contents trended to first decrease and then increase, except for irrigation amount of 0 m³·hm⁻², but the catalase activity decreased. Proline content tended to decrease with increasing nitrogen application rates (P < 0.05). Correlation analysis showed that there was no significant correlation between dry matter yield and photosynthetic or physiological characteristics of Italian ryegrass. Therefore, 1 800 m³·hm⁻² irrigation amount combined with 160 kg·hm⁻² nitrogen application rate had the best effects on yield and photosynthetic or physiological characteristics of Italian ryegrass grown in the breeding land.