灌淤土施氮后土壤硝态氮的动态变化

通过室内模拟试验,探讨不同水分条件下灌淤土施用不同氮肥后硝态氮随时间的变化规律,并在田间条件下,测定不同氮肥形态和数量对土壤硝态氮含量的影响。灌淤土施氮后土壤硝态氮含量变化与土壤含水量及氮肥种类有关。施肥9d后,土壤中的硝态氮迅速增加;土壤水分低于田间持水量的50%或水分过饱和都明显影响灌淤土的硝化作用;施用大颗粒尿素产生的硝态氮最少,淋失或流失的几率小。灌淤土土体中硝态氮的残留与施氮种类及数量有直接关系。施肥使土壤表层硝态氮显著增加,施用大颗粒尿素尤为突出,但施大颗粒尿素后,60cm土体中残留的硝态氮总量最少。随着施氮量增加,表层土体中硝态氮含量增加。合理的施肥水平一般不会造成硝态氮的大量累积,而过量施氮则导致硝态氮明显积累,对通气透水性好的灌淤土,容易造成硝态氮淋失。

Dynamics of nitrate content in Guanyu soil after nitrogen fertilization

Law of changes in nitrate under different soil moisture and supply of different forms and quantities of N fertilizer in Yinchuan alluvial plain were studied by means of field experiments and indoor cultivation.The results showed that nitrification process is directly related with soil moisture content and forms of N fertilizer.Nitrate obviously appeared 9 days after the application of N fertilizer.Nitrification process was restrained under dry or saturated soil water conditions.Granulation of urea can slow down nitrification process and form less nitrate than other forms of N fertilizer.Therefore,applying large-sized urea granules can reduce nitrate loss and increase N availability to plants.Nitrate increases in soil profile with the increasing of application rate of N fertilizer.Nitrate in the cultivated layer increases due to application of more N fertilizer,especially large-sized urea granules.However,granulated urea only provides the lowest amount of nitrate in the whole soil profile compared with the other forms of N fertilizer applied.The Nitrate content would not get up to a harmful level if N fertilizer is applied reasonably,but nitrate is accumulated in the 60 cm-deep soil profile under traditional N fertilizer application,easily causing nitrate leaching due to high aeration of Guanyu soil.