关中农田土壤物理状态与分析

摘要

针对关中农田土壤通气、透水能力下降,抗不良环境能力减弱,生产成本逐年递增的实际问题,以关中11个县区农田土壤为研究对象,以土壤耕作层厚度、容重及团聚体特征为指标,开展了现代利用强度及土壤管理模式下农田土壤物理状态及其退化特征研究.结果表明:关中地区土壤发生学层次厚度尽管很厚,但受下层土体紧实化的影响,农田土壤耕作层普遍浅薄,疏松良好的土壤耕作层厚度变化在5～21 cm.调查范围内耕作层厚度在20 cm左右的仅占18％,10～15 cm之间的占64％,＜10 cm占18％左右.关中地区农田0～20 cm耕层土壤容重变化在1.04～ 1.34 g·cm-3,平均容重为1.21 g·cm-3,属于良好物理状态;而20 ～ 40 cm土壤容重变化在1.46～1.70 g·cm-3之间,平均容重为1.58 g·cm-3,属于很紧实土壤状态.约36％的农田在20 ～ 40 cm处容重达到或超过了1.60 g·cm-3的极限容重值.用干、湿筛技术测定的土壤团聚体的组成,关中农田1～5mm的“(质量)优势团聚体”、团聚体的几何均重直径(GMD)、标准化平均当量直径(NMWD)以及土壤结构系数(Kctp)均显示,耕作层土壤团聚状态处于良好级别,其下层64％的土壤团聚状态较差,关中农田土壤团聚体水稳定性差,各地土壤团聚体状态以及稳定性差别明显.结论:关中地区农田土壤耕层变浅薄,是因为20～40 cm土层紧实化程度增大和犁底层上移与变厚所致;20～40土壤容重已经增大到极限值;0～20 cm土壤团聚体状态良好,但稳定性不强是引起其下层土壤紧实化的重要原因.关中农田土壤亚表层紧实化问题普遍,有愈加严重的发展态势.从空间上紧实化土层具有很强的隐蔽性,难以被人们所觉察,属于隐型土壤物理退化特征,不可小觑.%In the face of soil aeration and water permeability declining,the ability of resistance to harmful environment diminishing,and the productive cost increasing year by year in Guanzhong farmland,the farmland soil sample from 11 counties in Guanzhong was taken and the thickness of arable layer,the soil density and aggregate characteristics was determined to study the soil physical state and its degradation characteristics under the condition of modern utilization intensity and soil management.The results showed that the soil arable layer generally became thin because of the compaction of lower soil,although the thickness in Guanzhong area was very thick in soil genesis.The thickness of soil arable layer was 5 ～ 21 cm.The sample number of the thickness of about 20 cm accounted for only 18％,the sample for 10 ～ 15 cm accounted for 64％,the sample of less than 10 cm accounted for about 18％.The soil bulk density in 0 ～ 20 cm layer in Guanzhong farmland were 1.04 ～ 1.34 g· cm-3 and the average value was 1.21 g· cm-3,which is good physical state.However,the soil bulk density in 20～40 cm layer was from 1.46～ 1.70 g·cm-3 and the average was 1.58 g·cm 3.The soil density in subsoil layer for about 36％ of farmland reached or exceeded the limit value of 1.60 g · cm-3.Soil aggregate composition was determined by dry and wet sieving.The proportion of optimum aggregates of 1 ～ 5 mm,GMD,NMWD and coefficient of soil structure (Kctp) demonstrated that soil aggregate in arable layer was in good state,and 64％ of soil aggregate in subsoil layer was in poor state.The water-stability of aggregates in farmland was worse.The state and stability of soil aggregate differenced largely in Guanzhong farmland.The reason that the arable layer becomes thin might be the subsoil compaction happened in 20 ～ 40 cm layer and plow-pan moved up and thickened.The soil bulk density in 20 ～ 40 cm has increased to a limit value.In 0 ～ 20 cm layer,soil aggregates were in good condition,but its poor water stability was the important reason of subsoil compaction.Soil compaction in Guanzhong farmland was widespread and became more serious.The soil compaction was a concealed soil physical degradation.Thus,more attention should be paid to soilcompaction in subsoil.