Evaluation of efficiency of controlled-release N fertiliser on tartary buckwheat production

To provide reference for scientific management of nitrogen (N) fertiliser on tartary buckwheat, the effects of the mixed application of controlled-release N fertiliser (a kind of thermoplastic polymer-coated urea types that are characterised by a semi-permeable membrane) and common urea was studied in the main tartary buckwheat production area in China. In 2018 and 2019, a two-year field experiment was conducted a randomised block design with five treatments: (1) no nitrogen fertilisation (CK); (2) 100% N from common urea (T1); (3) 15% N from controlled-released urea fertiliser (plastic coated) + 85% N from common urea (T2); (4) 30% N from controlled-released fertiliser + 70% N from urea (T3); (5) 45% N from controlled-released fertiliser + 55% N of urea (T4). The N fertilisation rate was 90 kg N/ha in all fertilisation treatments. The results showed: (1) the mixed application of controlled-release N fertiliser and common urea was conductive to enhance the yield, dry mass, N uptake and apparent N fertiliser efficiency (NFE), compared with a single application of common urea. In two seasons, NFE was 38.6% (T1), 48.6% (T2), 53.6% (T3) and 53% (T4), separately; (2) the mixed application of controlled-release N fertiliser and common urea could significantly increase the soil inorganic N content in the soil surface layer and decreased the leaching loss of N; (3) with the increasing ration of controlled-release N fertiliser, the tendency of increasing N content of crop uptake and soil residual and decreasing rate of N loss and N surplus was visible. Overall, considered the indicators of grain yield, input cost, N utilisation and N balance, the suitable N fertilisation mode for tartary buckwheat production is the mixed application of 30% controlled-release N fertiliser and 70% common urea when 90 kg N/ha is applied.