不同氮肥用量对蔬菜硝态氮累积的影响

利用盆栽试验，研究了氮肥用量对蔬菜硝态氮累积的影响。结果表明，施用氮肥使蔬菜的生长量提高1.1～6.1倍，但增长并不与氮肥用量同步。氮肥用量较高时，蔬菜生长受到抑制，生长量有降低趋势;硝态氮含量却随氮肥用量增加而不断升高，两者呈显著正相关（r=0.933～0.957）。蔬菜各器官、部位的硝态氮含量存在明显差异。不施氮肥时，根的硝态氮含量大于茎叶，茎又大于叶;施氮后根的含量小于茎叶，茎小于叶;无论施氮与否，叶柄的含量均高于叶片。把蔬菜的生长、硝态氮吸收及还原转化联系起来分析，可以看出，增加氮肥用量虽然提高了硝酸还原酶活性，但硝态氮的还原作用仍小于吸收，从而导致蔬菜体内出现硝态氮累积。而且，随氮肥用量增加，硝态氮累积量的增加远超过了生长量的提高，使硝态氮含量迅速升高。

INFLUENCE OF NITROGEN RATES ON NITRATE ACCUMULATION IN VEGETABLES

Pot experiments with rape, chinese cabbbage and spinach to study the influence of nitrogen rates on nitrate accumulation in the vegetables were carrled out in greenhouse. Soil sampled from field of wheat. The results showed that application of certain amounts of nitrogen fertilizer increased these vegetable yields by 1.1 to 6.1 folds, but high nitrogen rates inhibited their growth. In contrast, nitrate contents in vegetables increased continuously with the increase of N rates, and significant positive correlation were found between the nitrogen rates and nitrate contents (r ranging from 0. 933 to 0. 957). The nitrate contents had significant difference with organs of vegetables. Without nitrogen fertilization, the nitrate contents were higher in roots than in shoot and higher in stems than in leaves. Application of nitrogen the nitrate contents were lower in the roots than in shoot and lower in stems than in leaves. However, the nitrate contents were always higher in petioles than in blades at any case. Comparing the vegetable growth, nitrate absorption and reduction found that nitrate reductase activities increased at high nitrogen level and nitrate reduction was less than absorption, so nitrate accumulation occured in the vegetables. Further, nitrate accumulation in plants increased more rapidly than hiomass growth with the increase of nitrogen rates. This might be the major cause for the rapid increase of nitrate contents in vegetables.