两种水稻土氮初级矿化和硝化速率及其与氮肥利用率的关系

RELATIONSHIPS OF FERTILIZER-N USE EFFICIENCY WITH GROSS N NITRIFICATION AND MINERALIZATION RATES IN TWO DIFFERENT PADDY SOILS

高氮肥施用量和低氮肥利用率是我国水稻生产可持续性发展面临的问题之一。氮肥损失途径与肥料进入土壤后的转化过程息息相关。了解水稻土中氮素转化过程并进行定量描述有助于提高人们对稻田氮素损失途径的认识水平。为此,开展了连续2年的大田实验,测定了稻麦轮作条件下江苏淮安碱性水稻土(潮黄土,pH=8.3)和宜兴中性水稻土(黄泥土,pH=6.2)作物氮肥利用效率;同时采用15N同位素稀释方法,开展室内好氧培养实验,估算了两种土壤中的氮素初级矿化和硝化速率,以此解释田间试验中氮肥利用率差异的原因。田间试验结果表明,在获得相似的水稻或小麦产量的情况下,淮安潮黄土氮肥需用量高于宜兴黄泥土,而氮肥利用率却低于宜兴黄泥土。15N室内培养实验结果表明,供试潮黄土氮素初级矿化和硝化速率均较黄泥土高,其较高的pH可能是主要原因。潮黄土中相对较高的初级矿化和硝化速率可能会导致更多的NO-3-N在土壤中短暂累积,不能被作物及时吸收利用的NO-3-N便可通过各种途径损失掉。这可能是造成两种稻田土壤田间氮肥利用率差异的原因之一。

Currently sustainable development of the rice cultivation in China is confronted with a series of problems, among which high N fertilization rate and low use efficiency of N fertilizer is one. Pathways of N loss are closely related to transformation processes of the fertilizer after it is applied into the soil. A better knowledge and quantitative description of the transformation processes in paddy soil would help understand how N is lost in the rice-wheat rotation system. For that, a 2-year field experiment was carried out in a paddy field of alkaline paddy soil （ Chaohuang Tu, pH = 8.3 ） in Huai＇an, North Jiangsu and a paddy field of neutral soil （ Huangni Tu, pH = 6.2） in Yixing, South Jiangsu to determine crop N re-covery rate. At the same time, an in-lab aerobic incubation was conducted to reckon primary N mineralization and nitrifi- cation rates in the two paddy soils, using the 15N isotope dilution method, so as to further explain causes to the difference in N use efficiency between the two soils in the experiment. The field experiment shows that to achieve similar crop yields, the alkaline paddy soil required a higher rate of N fertilizer than the neutral paddy soil, but was lower in fertilizer N use efficacy （ FNUE）. The incubation experiment shows that, both the gross N mineralization and nitrification rates were high- er in Chaohuang Tu than in Huangni Tu, which may be attributed to the higher pH in the former. Higher N mineralization and nitrification rates may lead to temporary accumulation of NO3--N, which can not be absorbed immediately by plants and then gets lost via a series of pathways. This may be one of the causes that lead to differences in FNUE between the two fields.