农田厚不饱和层硝态氮分布特征初探

Characteristics of nitrate distribution in deep unsaturated zone in farmland

利用G eoprobe(r)钻机获取深层连续土样,研究农田厚不饱和层硝态氮分布特征,并评估农田施氮污染地下水的潜力。研究发现在渗透性中等的土壤中,硝态氮已经淋溶到15 m以下,厚不饱和层中硝态氮分布按含量高低可分为三个明显区段:根系吸收层中含量区、吸收层下高含量区和深层低含量区。其中根系吸收区下的硝态氮含量明显高于吸收区;深层的硝态氮含量虽然较低,但累积量可能超过根区的累积量。硝态氮的这些分布特点表明地下水水质已经受到了很大威胁。吸收层下硝态氮含量的起伏明显受土壤的质地影响;在较深土层中与土壤水分含量也有明显的相关性。

In this study, the Geoprobe（r） direct push system was employed to obtain 15 meters of continuous soil core samples from the deep unsaturated zone of the cropland in North China Plain, so as to analyze the nitrate concentration in the soil samples and evaluate the risk of groundwater contamination by chemical fertilizer in this area. The results showed that, in the tested soil samples of medium permeability, the nitrate could be leached into the depth of more than 15 meters below ground surface. The distribution of nitrate in the deep unsaturated zone in such a typical setting could be separate into three zones： medium concentration zone in the root absorption area, high concentration zone below the root absorption area and low concentration zone in the deep subsurface area. The nitrate concentration below the root absorption area was obviously higher than that in the root absorption area. Although the nitrate concentration in the deep subsurface area was low, its accumulation might be higher than that in the root zone, therefore, the underlying groundwater was highly threatened by contamination. Soil texture obviously impacted the distribution of nitrate concentration below the root absorption area; and the nitrate concentration distribution was positively correlated with the soil moisture content in the deep soil profile.