京郊大白菜的氮素吸收特点及氮肥推荐

在京郊露地生产条件下,研究不同供N处理对秋季大白菜的生长、N吸收和土壤N矿化及损失的影响,并根据土壤-作物系统中N的借贷平衡原理确定大白菜N供应的合理目标值。结果表明,大白菜的产量和N吸收随施N水平的增加呈线性-平台的增长趋势。在作物的目标产量(120t/hm2)和N吸收数量(N200kg/hm2)的情况下,适宜的N素供应水平,即目标值为N350kg/hm2。大白菜的N吸收量随生育期逐渐增加,包心前期平均每周的N吸收量为N8.5kg/hm2,而在包心后期达到N220kg/hm2。在作物的整个生育期间土壤N的净矿化数量为N37kg/hm2,平均每周的土壤表观N损失为N7.8kg/hm2。这些参数有助于利用简单的N借贷平衡指导京郊秋季大白菜的推荐施肥。

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 N_min residue, these parameters are very practical in N recommendation based on balanced calculation for Chinese cabbage growth in Beijing Suburb.