地表覆盖对西北旱地土壤有机氮累积及矿化的影响

Effects of Different Surface Mulching on Soil Organic Nitrogen Accumulation and Mineralization in Dryland of Northwestern China

【目的】认识土壤氮素的转化和供应过程,是优化作物栽培和氮素养分管理的关键。【方法】本文采用5年田间长期定位试验的土壤,研究了地表覆草和覆膜栽培对旱地土壤氮素矿化和供氮能力的影响。【结果】与常规栽培相比,地表长期覆草会提高土壤氮素矿化势,降低矿化速率;覆膜则会降低土壤氮素矿化势,提高矿化速率,覆草、覆膜和常规栽培的矿化势分别为25.0—29.7、23.2—25.9、23.3—26.2mg.kg-1。不施氮时,覆草和覆膜均能提高土壤有机氮含量,增加土壤轻质有机氮含量;施氮后,覆草能增加土壤有机氮和轻质有机氮含量,但覆膜却降低了土壤有机氮和轻质有机氮含量。施氮240kg.hm-2时,地表覆草、覆膜和常规栽培土壤的有机氮含量分别为1.03、0.95和0.96g.kg-1,轻质有机氮分别为51、35和37mg.kg-1。【结论】作物生长过程中,地表覆草栽培能使土壤将较多的矿质氮转化形成可矿化有机氮;覆膜栽培则不利于土壤的有机氮累积。因此,覆草栽培虽增加了土壤氮素供应能力,但为实现作物增产,需增加氮肥投入或在作物需氮较多的生长阶段补充氮肥,覆膜栽培则需要注意配施有机肥。

[Objective] Understanding soil nitrogen transformation and supplying process is the key for optimizing crop cultivation and nitrogen managements. [Method] In this paper, soils were sampled from a 5-year-long field experiment to study the effects of different soil surface mulching on soil organic nitrogen accumulation and mineralization in dryland of northwestern China. [Result] The results showed that compared to conventional cultivation, long term surface mulching with straw increased soil nitrogen mineralization potential but decreased mineralization rate. Mulching with plastic-film decreased nitrogen mineralization potential, but increased mineralization rate. The nitrogen mineralization potential for the conventional cultivation, straw mulching and plastic film mulching was 25.0-29.7, 23.2-25.9 and 23.3-26.2 mg·kg^-1, respectively. Without N application, straw and plastic-film mulching increased soil organic nitrogen and light fraction organic nitrogen contents. When N was fertilized, straw mulching could increase soil organic nitrogen and light fraction organic nitrogen contents, while plastic-film mulching decreased their contents. At N rate of 240 kg·hm^-2, the organic nitrogen content was 1.03, 0.95 and 0.96 g·kg^-1, and the light fraction organic nitrogen content was 51, 35 and 37 mg·kg^-1 for the conventional cultivation, straw mulching and plastic film mulching, respectively. [Conclusion] It is concluded that surface mulching with straw causes soil to immobilize more mineral N into mineralisable organic N, while with plastic film is not beneficial to organic nitrogen accumulation. Therefore, in order to increase crop yield, more nitrogen fertilizer is needed or supplemental N fertilizer should be applied at the key nitrogen requirement stage under straw mulching cultivation as it could increase soil N supply capacity. For plastic film mulching, more attention should be paid to application of organic fertilizer.