Characteristics of N uptake and N recommendation for autumn Chinese cabbage in Beijing Suburb

Effects of different nitrogen supply levels on the growth, N uptake of autumn Chinese cabbage(Brassica campestrisL. ssp Penkinensis (Lour) Olsson), net N mineralization and N loss in soil were investigated in the open field of Beijing Suburb The target value of optimized N supply level for Chinese cabbage was also decided based on the principle of N balance model The results showed that the yield and N uptake in Chinese cabbage increased with applied N rate as linearplateau trends (y=3085+10.5x,when 0318;y: Dry matter yield of Chinese cabbage, kg/hm2; x: N supply level, N kg/hm2) Under the target yield of 120 t/hm2 and target N uptake of N 120 kg/hm2, the optimum N supply level was N 318 kg/hm2, however considering the risk of yield reduction, N 350 kg/hm2 should be adapted in practice N uptake amount by Chinese cabbage increased with developing stage During the six weeks after seeding (before head forming), average weekly N uptake amount was N 8.5 kg/hm2, however, after heading forming until harvest, the value increased up to N 220 kg/hm2 During the crop growth stage, average soil net N mineralization amount was N 37 kg/hm2 and apparent weekly N loss was N 7.8 kg/hm2 Considering soil Nmin residue, these parameters are very practical in N recommendation based on balanced calculation for Chinese cabbage growth in Beijing Suburb.