半干旱地区不同土壤团聚体中微生物量氮的分布特征

The Distribution Characteristics of Microbial Biomass Nitrogen in Different Soil Aggregate in Semi-arid Area

从内蒙古半干旱地区的林地、草地和耕地采集7个土地利用方式不同的土壤样品,利用干筛法得到>5mm、5～2mm、2～1mm、1～0.5mm、0.5～0.25mm和<0.25mm的土壤团聚体,并测定各级团聚体中的全氮、微生物量氮、K2SO4浸提氮含量。结果表明,不同的土地利用方式,由于其输入的有机物质数量和种类以及肥料管理不同,直接影响到土壤全氮、K2SO4浸提氮、微生物量氮的含量及其在团聚体中的分布。土壤全氮、微生物量氮和K2SO4浸提氮分别为0.67～2.06g·kg-1、11.40～71.03mg·kg-1和1.28～4.60mg·kg-1。有灌溉条件的耕地土壤氮的含量最高,退化草地最低。不施肥的土壤,其小团聚体中全氮和微生物量氮含量明显低于大团聚体;而进行灌溉的耕地土壤,由于无机氮肥和有机物质输入量都比较高,不仅其全氮含量比较高,而且小团聚体中全氮和微生物量氮含量也比较高,说明在低肥力条件下土壤氮素首先在大团聚体中循环,这表明在自然土壤生态系统中,大团聚体中氮素的循环转化比小团聚体中的更加重要。

Seven soils were collected from forestland, grassland and cropland in semi-arid area of Inner Mongolia. The soil aggregates of >5 mm, 5-2 mm, 2-1mm, 1-0.5 mm, 0.5-0.25 mm and <0.25 mm were obtained with a dry-sieving method. The total N (TN), microbial biomass N (MBN), K2SO4-extractable N (K2SO4-N) of the soil aggregates were separately determined. The results showed that the different inputs of organic materials and nitrogen fertilizer of the sampled soils significantly affect not only the contents of total N, microbial biomass N and K2SO4-extractable N, but also their distributions in soil aggregates. The total N, microbial biomass N and K2SO4-extractable N were in the ranges of 0.67-2.06 g·kg-1, 11.40-71.03 mg·kg-1and 1.28-4.60 mg·kg-1, respectively. The irrigated soil (No. 6) had the highest value, but the lowest value was in the grassland soil (No.7). Generally, the small aggregates contained significantly lower total N and microbial biomass N than the larger aggregates in the soils with low inputs of organic materials and N fertilizer. In contrast, the small aggregates contained much higher total N and microbial biomass N than the larger aggregates in the soils with high input. It is implied that, under natural condition, N was firstly cycled in the large aggregates. Thus, the N of the large aggregates may play much more important role in natural low nutrition condition than that of the small aggregates.