Manure Application Effects on Nitrogen Uptake and Distribution in Organic Chinese Flowering Cabbage Based on 15N-tracing

Abstract The application of large amounts of manure nitrogen (N) in Northwest China has had a serious negative impact on the sustainable development of regional organic agriculture and ecological environmental protection. Field experiments were conducted in three crop cycles in Ningxia, Northwest China, to study the effects of different manure application rates on the N absorption and utilization of Chinese Flowering Cabbage (CFC) and N distribution characteristics of manure, which were carried out on the basis of 0(M 0 ), 300(M 300 ), 600(M 600 ), 900(M 900 ), 1200(M 1200 ) kg N·hm -2 manure N rates by setting an 15 N micro-area. Results showed that the 15 N absorption in each crop of CFC showed a parabola trend of "low high low" with an increase in the amount of manure, and the 15 N absorption of the M 900 treatment was the highest, which increased by 64.3 % compared with that of the M 1200 treatment ( P <0.05). After three crops of CFC, only 10.2–24.0% of manure N was absorbed by the crops, and 39.0–54.3% remained in the 0–100 cm soil layer, with a loss ratio of 35.5–48.5%. The manure N absorption rate under M 900 treatment reached the maximum (24.0 %), and the amount of soil residual (351.11 kg·hm -2 ) was greater than the loss (333.28 kg·hm -2 ). N absorption in the M 1200 treatment was 39.2 % lower than that in M 900 ( P <0.05), and the loss (581.17 kg·hm -2 ) was greater than that of the residue (487.64 kg·hm -2 ). The residual 15 N was mainly distributed in the 0–40 cm soil layer, and the residual amount was 127.65–390.32 kg·hm -2 , which accounted for 78.1–81.3% of the total residual amount. The nitrate-N content in the 0–20 cm and 20–40 cm soil layers increased with increasing manure application rates, and there was no significant difference between the M 900 and M 1200 treatments. However, the NO 3 – - 15 N content in the 40–100 cm soil layer in the M 1200 treatment was 1.2 times higher than that in the M 900 treatment ( P <0.05). Therefore, considering the absorption, residue, and loss of manure N in crops, it can be concluded that a manure N application rate of 900 kg N·hm -2 is the most favorable for the production of three consecutive crops of CFC.