旱地小麦地表覆盖对土壤水分硝态氮累积分布的影响

在黄土高原南部半湿润易干旱地区,通过长期田间定位试验,研究了不同地表覆盖对第3季冬小麦生长、氮素吸收及土壤水分和硝态氮累积分布的影响。结果表明,无论地表覆盖能否促进小麦生长及其对氮素的吸收,在收获期均能提高表层土壤水分;覆膜栽培增加表层硝态氮含量,覆草也在高量施用氮肥时,提高表层硝态氮的累积。而地表覆盖对耕层以下土壤水分和硝态氮累积的影响与施氮量、作物生长及其对氮素吸收利用有关。覆膜在促进作物生长、提高氮素吸收的同时,降低了深层土壤水分及其硝态氮的累积,且随施氮量的增加降低幅度增大;覆草在不施氮肥和施氮120kg·hm^-2时未能促进小麦生长,但有增加深层土壤水分的趋势,而高量施用氮肥,明显提高了小麦地上部生物产量及其对氮素的吸收,降低了深层土壤水分;同时发现,无论施氮与否覆草均降低了下层土壤硝态氮的累积。在高量施用氮肥的情况下,采用地表覆盖,不仅能够促进作物生长、提高氮素吸收,还能有效降低氮素在土壤中的累积及其向下层淋溶。

Effect of Different Soil Surface Treatment on Moisture and Nitrate Nitrogen Accumulation and Distribution in Wheat Field Soil Profiles in Dryland

A long-term field experiment was conducted in a sub-humid area prone to droughts at south part of the Loess Plateau, to study the effects of different soil surface treatment on winter wheat growth and nitrogen uptake, water and nitrate nitrogen accumulation and distribution in soil profiles. The results showed that, soil water and NO3^-N in 0-20 cm obviously increased under plastic sheet mulching with the three N rates, while under wheat straw mulching, soil moisture increased too, and NO3^-N also significantly increased in high N （240 kg·hm^-2）. However influence of different soil surface mulching on soil moisture and nitrate nitrogen in deep soil layers varied with N rate, wheat growth and N uptake. Plastic sheet mulching promoted crop growth and N uptake, at the same time, decreased soil water and NO3-N, and the amounts of them were larger with the N rate increased. Wheat straw mulching didn＇t increase crop growth and had the trend of increasing soil water in deep soil layers at N rates of 0 kg·hm^-2 and 120 kg·hm^-2. When N rate increased to 240 kg ·hm^-2, wheat straw mulching increased shoot biomass and N uptake obviously, and decreased soil water in deep soil layers. Wheat straw mulching decreased NO;-N in deep soil layers at the three N rates. Therefore, soil surface mulching with high N rate not only increased crop growth and N uptake, but also decreased the amount of nitrate nitrogen accumulation in 0-300 cm and reduced nitrate nitrogen leaching into deep soil layers.