半干旱区生态过程变化中土壤硝态氮累积及其在植物氮素营养中的作用

半干旱区农田生态系统石灰性土壤施入的氮肥和有机氮矿化产物,除植物吸收、微生物固定、粘土矿物固定、挥发损失和反硝化损失外,有相当一部分最终以NO3--N形态残存在土壤中。土壤剖面中的残留NO3--N通过对流和扩散等途径,逐渐向深层移动,脱离根区。影响土壤剖面NO3--N残留累积和淋溶的主要因素包括施氮量、植物吸氮量、前作收获后的植物残留物、氮肥种类、施氮方式和降雨量等。残留NO3--N本身具有很高的生物有效性,但能否被植物吸收利用,关键在于残留NO3--N所在深度及其是否能够到达根区。在半干旱区降雨量较高的雨季,NO3--N向深层移动,而在较干旱条件下即使土壤剖面深层NO3--N,也可随水分上移供根系利用,因此土壤剖面中累积的残留NO3--N显著影响氮肥肥效果,许多地方用一定深度土层中累积的NO3--N作为土壤供氮指标,以减少NO3--N的淋溶损失和提高氮肥肥效。过去对半干旱地区土壤剖面中NO3--N的研究主要涉及3方面,一是土壤剖面中NO3--N的残留累积及其影响因素,二是与根系分布深度相适应土层中残留NO3--N对氮肥肥效的影响,三是根据土壤剖面中的残留NO3--N确定农田作物施氮量。在分析过去研究结果的基础上,提出了今后需进一步深入研究的科学问题。

Accumulation of soil nitrate nitrogen in the process of ecological and its effcts in plant nitrogen nutrition in semiarid areas

Of applied N fertilizer and mineralized organic N in calcareous soil in the agro-ecosystem of semi-arid areas, apart from plant uptake, microbial-fixed, clay mineral-fixed, volatilization loss and denitrification loss, significant amount of these N remains in the soil as NO_3~--N. Residual NO_3~--N in soil profile moves to depth by convection and diffusion, leaving the root zone step by step. The main factors that affect the accumulation and leaching of NO_3~- includes: N input, plant take up, plant residual after pro-harvest, N fertilizer kinds, N fertilizer applying manner and rainfall et al. Residual NO_3~--N itself has high bioavailability. Whether it can be taken up or not depends on the depth of NO_3~--N and the distance to the root zone. During the heavy rainfall season in semiarid areas, NO_3~--N moves to depth easily; but in dry condition, even NO_3~--N in deep soil can move up with water to the root zone and be taken up. As a result, residual NO_3~--N accumulated in soil profile impacts N fertilizer use efficiency remarkably. In many regions, residual NO_3~--N at certain depth is used as the index of N supplied N to soil to reduce the NO_3~--N leaching and improve N fertilizer use efficiency. According to past researches of NO_3~--N in soil profile in semiarid areas, three aspects are concerned: first, accumulation of residual NO_3~--N in soil profile and the factors that affects it; second, residual NO_3~--N that coincides with root depth contributes to N fertilizer use efficiency; third, the determination of rational N input according to residual NO_3~--N in soil profile. On the basis of the analysis above, a few scientific problems that should be solved in future research are emphasized.