尿素和KNO3对水稻土无机氮转化过程和产物的影响 Ⅰ无机氮转化过程

EFFECTS OF UREA AND KNO_3 ON PROCESSES AND PRODUCTS OF INORGANIC NITROGEN TRANSFORMATION IN PADDY SOILS I.PROCESSES OF INORGANIC NITROGEN

用15N分别标记尿素和KNO3,研究了淹水条件下 ,黄泥土和红壤性水稻土的无机氮转化过程及尿素和KNO3对氮素转化过程的影响。结果表明 ,淹水条件下 ,土壤中存在15NH+4 的成对硝化和反硝化过程。红壤性水稻土15NH+4 硝化只检测到15NO- 2 ,但有反硝化产物15N2 生成 ,因此 ,很可能存在着好气反硝化过程。15NO- 3浓度的下降符合一级反应方程 ,黄泥土的速率常数几乎是红壤性水稻土的 1 0倍。反硝化过程和DNRA过程共同参与15NO- 3的还原。加入尿素提高土壤pH ,增加黄泥土DNRA过程对反硝化过程的基质竞争能力 ,但反硝化过程仍占绝对优势。加入尿素或KNO3改变土壤pH是导致对无机氮转化影响有所不同的主要原因 ,浓度的作用较为次要。

Summary By using 15 N techniques, effects of urea and KNO 3 on processes and products of inorganic nitrogen transformation in Hydragric paddy soil and Gleyic paddy soil, collected from Wuxi and Yingtan, respectively, were investigated under flooding conditions at 25℃. The results showed that coupled nitrification and denitrification of 15 NH + 4 occurred in both paddy soils. Oxidation of 15 NH + 4 in the Gleyic paddy soil amended with 15 N labeled urea alone was terminated at the product of 15 NO - 2, but denitrification product 15 N 2 was observed, implying a high possibility of aerobic denitrification. The decrease in 15 NO - 3 concentration in both soils, followed the first order reaction. The reaction constant of the Hydragric paddy soil was about 10 fold that of the Gleyic paddy soil. Addition of urea raised soil pH and stimulated DNRA process in the Hydragric paddy soil, and both denitrification and DNRA processes in the Gleyric paddy soils. However, denitrification was a dominant process in 15 NO - 3 transformation. The differences in the effects of urea and KNO 3 on the processes and products of inorganic nitrogen transformation in paddy soils would primarily result from their different effects on soil pH and secondarily from concentration effect.