宁夏不同地区农田土壤矿质氮的空间变异特征

Spatial variability of soil mineral nitrogen of farmlands in different regions of Ningxia

在宁夏灌区和旱区共计选定肥力水平不同的30块农田,分别采集了0～120 cm深土壤剖面样品和小麦植株样品,测定了土壤铵、硝态氮含量和小麦地上部含氮量,分析了土壤矿质氮的空间变异性及其与小麦吸氮量的关系.结果表明,在0～120 cm深土壤剖面中,NH4-N、 NO3-N和矿质氮含量及其累积量,灌区土壤显著高于旱区土壤,测点之间存在极显著差异,变异系数相当高.但在土层间不论灌区还是旱区变化不明显,在剖面上下分布比较均匀.矿质氮含量在土层间存在着正相关.在0～120 cm深土壤剖面中,矿质氮累积量在灌淤土、黑垆土、黄绵土和灰钙土间差异较大,平均分别为370.0、 155.1、 117.5和61.0 kg/hm2.其累积量与小麦籽粒产量、生物学产量、地上部总吸氮量之间呈极显著正相关,表明土壤较深层次的矿质氮对作物吸氮量也具有重要贡献.

Soil samples of 0-120 cm depths and plant samples of wheat were taken from 30 farmlands with different fertility levels in both irrigated and dryland regions in Ningxia. The NH4-N contents, NO3- N contents and nitrogen uptake amount of plant were determined in order to investigate the spatial variability of soil mineral nitrogen and the relations between distribution of mineral nitrogen in soil profiles and nitrogen accumulated rates in aboveground parts of wheat. The results showed that the contents of NH4-N, NO3-N and mineral nitrogen at the depths of 0-120 cm in irrigated regions were significantly higher than that in dryland regions. There were very significant differences between different soil samples, and the variation coefficients were quite high. However, there were no significant differences between different soil layers either in irrigated regions or in dryland regions, and their distributions in all profiles were relatively even. There were obvious positive correlations between the contents of mineral nitrogen at different depths. There were evident differences of accumulated amounts of mineral nitrogen in 0-120 cm among different soil types, such as irrigating warped soil, dark loessial soil, cultivated loess soil and sierozem, the amounts of which were 370. 0, 155. 1, 117. 5 and 61. 0 kg/hm^2, respectively. The accumulated amounts of mineral nitrogen in soil profiles were positive correlated with the yield, biomass and nitrogen uptake of wheat. Thus it can be considered that the mineral nitrogen in deeper soil layers makes an important contribution to nitrogen uptake of plants.