Effect of water and nitrogen on the yield and quality of forage rape grown after wheat in South Xinjiang

A field randomized block experiment was conducted to investigate the effects of water and nitrogen on the yield and quality of multiple cropped forage rape after wheat harvest, by analyzing the variation characteristics of rapeseed yield and its four typical feed quality indicators under different water and nitrogen treatments through fuzzy similarity priority ratio method. The experiment included two factors:irrigation quota and nitrogen application rate; irrigation quota was 3 000 m³·hm^-2 (low water), 4 500 m³·hm^-2 (middle water), and 6 000 m³·hm^-2 (high water) (W1, W2, W3); nitrogen application rates were 140.6 kg(N)·hm^-2 (low nitrogen), 187.5 kg(N)·hm^-2 (medium nitrogen), and 234.4 kg(N)·hm^-2 (high nitrogen) (F1, F2, F3). The results showed that the suitable irrigation and nitrogen levels had significant interaction advantages on fresh weight, dry weight, yield, and quality of forage rape, while an excess or deficiency in irrigation and nitrogen levels reduced mutual advantage. The fresh weight, dry weight, and yield of forage rape under the same irrigation quota improved with the increase in nitrogen application rate. Under the same nitrogen application rate, the fresh weight, dry weight, and yield of forage rape increased with the increase in irrigation quota. Improving irrigation quota was better than increasing the nitrogen application rate. Yield under high water + medium nitrogen treatment increased by 86.90% when compared with yield under low water + low nitrogen treatment. Nitrogen application rate and irrigation-nitrogen application interaction significantly affected the quality of forage rape; in W2F2 treatment, crude protein content increased by 36.91% when compared with W3F3 treatment. The neutral-detergent fiber under W2F1 treatment was the lowest, at 32.66%, significantly lower than that under W3F3 treatment. The acid-detergent fiber under W3F1 treatment was the lowest (24.74%), which was lower than that under W3F3 treatment by 16.49%. The crude fat content was the highest under W3F3 treatment, at 1.45%. Comprehensive consideration of yield and quality revealed that the suitable water and nitrogen application measures for cultivating forage rape in South Xinjiang was high water and high nitrogen6 000 m³·hm^-2, 187.5 kg(N)·hm^-2.