由于土壤颗粒的选择性沉降,弱结构农田中水耕作用可导致耕层内上下之间物质组成的差别.为了解这种差异化是否会影响土壤性状的分异,本文选择代表性农田比较分析了水耕与旱耕条件下耕作层内上下部之间土壤性状的差异,并与结构发育良好的土壤进行了比较.结果表明:长期水耕的弱结构农田耕作层上下土壤之间颗粒组成、有机质、全氮含量、CEC、有效磷、速效钾、微生物生物量碳和Cu、Zn、Cd、Pb的含量均存在明显的分异,粗颗粒(砾石和砂粒)由上至下增加,而细颗粒(粘粒)从上至下减少.从0～2 cm 土层至18～20 cm 土层,土壤有机质、全氮、CEC分别下降达49.77％、48.77％和38.25％;土壤有效磷、速效钾和微生物生物量碳分别下降21.23％、13.54％和29.24％;从0～4 cm 土层至16～20 cm 土层,Cu、Zn、Cd 和 Pb 的含量分别由 27.43～28.33、65.45～71.43、0.13～0.15、24.73～27.65 mg/kg 下降至23.74～24.32、53.66～54.54、0.053～0.067、18.78～19.54 mg/kg;但土壤pH的变化不明显.结构良好的农田长期水耕对以上性状的影响较小或没有影响.长期旱耕的耕作层中有机质、全氮、CEC、速效养分、微生物生物量碳和Zn、Pb含量也呈上高下低的趋势,但上下之间的差异较小,对耕作层中颗粒组成、pH、Cu和Cd的分布无明显影响.研究认为,长期水耕可导致弱结构耕作层土壤性状的非均质化,可能会影响作物对土壤养分的吸收,应重视对其结构的改良.
Study on Micro-stratification of Soil Properties in Weak Structure Topsoil under Hydroponic Tillage Condition
Due to the selective settlement of soil particles,hydroponic tillage in weakly structured farmland soil can lead to the difference in material composition between the upper and lower parts of the cultivated layer.To understand whether this difference will result in the differentiation of soil properties,this paper selected representative farmlands,compared and analyzed the differences in soil properties between the upper and lower parts of the tillage layer under the hydroponic and dry tillage,and also compared them with the well-developed structure soil.The results showed that there were significant differences in particle composition,organic matter,total nitrogen content,CEC,available phosphorus,available potassium,microbial biomass carbon and the contents of Cu,Zn,Cd and Pb between the upper and lower soils of the weak structure farmland subjected to long-term hydroponic tillage condition.The coarse particles(gravel and sand)increased from top to bottom,while the fine particles(clay)decreased from top to bottom.From 0-2 cm soil layer to 18-20 cm soil layer,soil organic matter,total nitrogen and CEC decreased by 49.77% ,48.77% and 38.25% ,respectively,and soil available phosphorus,available potassium and microbial biomass carbon decreased by 21.23% ,13.54% and 29.24% ,respectively.From 0-4 cm soil layer to 16-20 cm soil layer,the contents of Cu,Zn,Cd and Pb decreased from 27.43-28.33,65.45-71.43,0.13-0.15 and 24.73-27.65 mg/kg to 23.74-24.32,53.66-54.54,0.053-0.067 and 18.78-19.54 mg/kg,respectively.However,the change in soil pH was not obvious.Long term hydroponic tillage in well structured farmland had little or no effect on the above characters.The contents of organic matter,total nitrogen,CEC,available nutrients,microbial biomass carbon,Zn and Pb in the soil tillage layer under long-term dry tillage also decreased with depth,but the difference between the top and bottom was small,and the tillage had no significant effect on the distribution of particle composition,pH,Cu and Cd in the tillage layer of well structured soil.The study suggested that long-term hydroponics tillage could lead to the micro-stratification of soil properties in the weak structure tillage layer,lead to material heterogeneity,affecting the absorption of soil nutrients by crops.Attention should be paid to the improvement of structure for the weak structure tillage layer.
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