黄土高原长期培肥土壤团聚体中养分和酶的分布

Distribution of nutrients and enzymes in Loess Plateau soil aggregates after long-term fertilization

土壤养分和生物酶是衡量土壤肥力的指标,土壤团聚体性质则决定了土壤物理结构的好坏,探讨不同培肥措施下土壤养分和生物酶在团聚体中的分布,对合理培肥和改善土壤性状具有重要的实际意义。对连续25a的长期有机培肥定位试验地进行测定,结果表明:培肥增加了大级别土壤团聚体、特征微团聚体的数量,显著地改善了土壤结构。培肥土壤团聚体平均重量直径、特征微团聚体CF0.01较无肥对照土壤有显著增加。长期培肥增强了土壤化学、生物性质的“微域”变异性。相同培肥措施下土壤主要养分含量和酶活性均随土壤团聚体直径的增大而减小。除厩肥处理土壤碱性磷酸酶和蔗糖酶外,其它各培肥土壤的养分含量和酶活性均在<0.01mm级别特征微团聚体中含量高、活性大。相同级别团聚体和特征微团聚体中,养分含量和酶活性在不同培肥土壤间基本表现出施厩肥处理>施秸秆处理>施化肥处理>对照的规律性。将团聚体的含量和养分含量或酶活性在团聚体中的丰度结合考虑,发现>5mm级别团聚体中养分含量或酶活性对土壤的贡献率最大。结果充分地显示着土壤性质在不同空间尺度下、不同管理措施下变异的复杂性和多样性。

The plant nutrient and microbial enzyme concentrations in a soil, and the degree of soil aggregation reflect the quality of the soil＇s chemistry, biology, and physical structure respectively. Each of these throe measures responds to a soil＇ s long-term fertility management： long-term applications of either organic or mineral fertilizers will strongly influence both the levels of plant nutrients and microbial activity, and the soil physical structure. Insight into the soil quality may therefore also be gained from the relationship between these three measures. Our aim was investigating the influence of different fertilization regimes on nutrient and enzyme levels in soil aggregates, as well as the degree of aggregation itself. We chose four treatments from the long-term fertilization experiment on the Loess Plateau at Northwest Science and Technology University of Agriculture and Forestry, Shaanxi, China, whicli was established in 1977. Treatments varied the fertilizer material——maize straw, manure, chemical fertilizer, and control （no fertilizer） with fertilizer being applied after both plowing and planting. The experiment used a randomized complete block design with three blocks and 12 plots measuring 19.8 m^2 . A wheat-maize crop rotation in a year, commonly used in the region, was adopted for this experiment. The soil in the study site is a heavy loam Lou soil （Earth-cumuli-ortho anthrosols according to the Chinese classified system） with a average fertility level. After 25 years of consistent crop rotation and fertilization, soil samples were collected wheat. Topsoil （0 - 20cm） samples were collected using a five-point method in each plot. in 2002 just before planting the winter Samples were air-dried, then machinesieved into five aggregate size fractions： 〉 5mm, 2 - 5mm, 1 - 2mm, 0.25 -1mm, and 〈 0.25mm. After passed through 1mm sieve, micro-aggregates were classified into two parts divided by 0.01 mm by using physical shaking and sedimentation. Aggregate size fractions were then passed through 1mm and 0.25mm sieves prior to nutrient and enzyme analysis. Soil organic matter, total N, and total P were measured in duplicate using standard methods. Enzyme analysis was performed in triplicate ： soil urease by the Hoffman method, invertase by the T. A. ЩepσaKoBa method, and alkaline phosphatase by the Ф X. XaЗHea method. All fertilization increased the degree of aggregation and the quantity of aggregates in the soil, significantly improving soil structure over the control treatment. Mean weight diameter of soil aggregates, and C/F0.01 of micro-aggregates increased from the control to the fertilizer treatments. Long-term fertilization amplified the variance of soil chemical and biological properties within soil microenvironments. Within a given treatment, nutrient content and enzyme activity tended to decrease with increasing aggregate size, with the highest values generally occurring in the 0.01mm characteristic micro-aggregates. Nutrient and enzyme levels followed the pattern manure 〉 maize straw 〉 chemical fertilizer 〉 control across all aggregate size fractions. Despite their lower concentrations of nutrients and enzymes, large aggregates accounted for most of the nutrients and enzymes in the topsoil. There was a significant positive correlation between nutrient levels, enzyme levels, and aggregate size, showing a consistent impact of fertility regime on soil quality.