Effects of Nitrogen Fertilization on Yield and Nitrogen Utilization of Film Side Planting Rapeseed (Brassica napus L.) Under Different Soil Fertility Conditions

Film side planting (FS) is a new water-saving and drought-resistant technology in dryland of southwest China, and nitrogen (N) is a main yield factor. However, the optimal N amount for FS rapeseed is unknown, especially in different soil fertility. Field experiments with N amounts (0, 60, 120, 180, 240, 300, and 360 kg ha −1 ) for FS rapeseed arranged in four soil fertility levels (divided into 1.5 t ha −1 based on the 5-year average rapeseed yield of not fertilizing, named respectively by F1, F2, F3, and F4) were conducted to analyze N utilization and yield. Besides, relationship between yield and N amounts was also discussed. The lower the soil fertility, the higher N amounts achieving high yield. Dry matter, N accumulation, N use efficiency, N agronomic efficiency, and effective pods were greatest for 360, 300, 240, and 180 kg ha −1 under F1, F2, F3, and F4 respectively. Eventually, 360, 300, 240, and 180 kg ha −1 obtained 27.31 ~ 242.32%, 35.26 ~ 129.44%, 15.92 ~ 142.00%, and 15.79 ~ 109.65% significantly greater yield than other N treatments under F1 and F2 (except 360 kg N ha −1 ) and F3 and F4 (except 240 kg N ha −1 ) respectively. Based on yield-N production function, the maximum rapeseed yields were obtained for F1 at > 360 kg ha −1 N, for F2 at > 360 kg ha −1 N, for F3 at 312 kg ha −1 N, and for F4 at 272 kg ha −1 N. Therefore, the optimal N amount for FS rapeseed under low soil fertility was 360 kg ha −1 or more and under high soil fertility was 272 ~ 312 kg ha −1 .