日光温室白萝卜生产系统的氮素利用与平衡研究

在日光温室条件下，研究了不同氮素供应水平对白萝卜（Raphanus sativus L．）氮素利用和土壤硝态氮累积动态，并对土壤-作物体系的氮素表观平衡进行了评估。结果表明，随氮肥用量的增加，白萝卜产量和干物质累积量均没有显著升高，但根块内富集的硝酸盐含量显著增加。增施氮肥对白萝卜维生素C（Vc），可溶性糖和可溶性蛋白含量没有显著影响；随施氮量增加白萝卜根块氮素吸收量显著增加，当季氮肥利用率降低；当氮肥用量低于推荐施氮量（有机肥＋200kg urea—N·hm^-2）时，整个白萝卜生长期，根层（0～60cm）土壤硝态氮均处于耗竭状态。当施氮量高于推荐施氮量时，根层硝态氮下降幅度减小，并在播种30d以后呈上升趋势；土壤一作物体系中播前无机氮（Nmin）和氮肥投入是主要输入项，输出项中以土壤无机氮残留和作物吸收为主。随施氮量的增加，氮素表观平衡值和土壤残留Nmin明显增加。系统氮素盈余量随施氮量的增加而增加。结合当地地力条件，在有机肥和磷钾肥配施的基础上，秋冬季白萝卜施氮量应控制在200kg·hm^-2以内。

Nitrogen Utilization and Balance of Raphanus sativus L. Production System in Greenhouse

In intensive agricultural systems, excess application of nitrogen（ N ） fertilizer has been a common phenomenon. Although N is an essential nutrient to crops, traditional N management is difficult to maximize crop yields while reduce its losses to the environment. One major reason is that the transformation and fate of N fertilizer in agricultural soils as largely affected by crop N uptake is still not very clear under specific production systems. The objective of this study was to analyze the effect of different N rates on Raphanus sativus L. N utilization and dynamics of nitrate in soil layers, then evaluate N balance in the soil-vegetable system. The trial included six fertilization treatments as follows：No, no N fertilizer and manure; N1, chicken manure 6 326 kg ·hm^-2, N2, chicken manure 6 326 kg ·hm^-2＋100 kg urea-N ·hm^-2; N3, chicken manure 6 326 kg·hm^-2 ＋200 kg urea-N·hm^-2; N4, chicken manure 6 326 kg ＋300 kg urea-N ·hm^-2 ;N5, chicken manure 6 326 kg＋1 015 kg urea-N·hm^-2, respectively. All treatments replicated three times and arranged in a completely randomized design. The results showed that the yield and the dry matter of Raphanus sativus L. were not remarkably increased with the N fertilizer rate, but the concentration of nitrate in Raphanus sativus L. increased significantly with increased N level. There were no obvious treatment effects on vitamin C, soluble sugar and protein contents in Raphanus sativus L. by increased N fertilizer rate. The accumulation of N in Raphanus sativus L. root was increased and the efficiency of N was decreased with the N fertilizer rate. When the N fertilizer rate was lower than 200 kg urea-N·hm^-2, the nitrate of 0-60 cm soil layer was exhausting during the whole growth period. When the N fertilizer rate was higher than 200 kg urea-N ·hm^-2, the decreased extent of the nitrate of 0-60 cm soil layer was reduced and began increasing 30 days later; In the system of soil and Raphanus sativus L., N input mainly came from the application of N fertil