半湿润区长期施肥对土壤结构体分形特征的影响

Effects of long-term fertilization on fractal features for soil aggregates in semi-arid farmland ecological system

利用黄土高原南部半湿润地区长达25年田间肥料定位试验0-20cm土层土样，研究了长期不同施肥模式与土壤结构体大小、结构体分形特征与土壤肥力的相互关系。结果表明，长期不同施肥模式下土垫旱耕人为土结构体分形特征存在一定差异：7种施肥处理土壤结构体分形维数分布在2．4388～2．6363之间，其中以化肥＋厩肥处理土壤结构体分形维数最大，不施肥土壤结构体分形维数最低，说明化肥与有机肥长期配施对土壤团聚体结构分布影响较大。相关分析发现，土壤结构体分形维数与5～2mm团聚体间具有极显著的正相关关系（r=0．994，P〈0．01）；与土壤有机碳、全氮、硝态氮、有效磷含量均具显著正相关关系，与土壤碳氮比（C／N）呈显著负相关关系。在长期不同施肥模式下，分形维数对土壤性质变化的边际量亦有明显差异：土壤结构体分形维数每增加一个单位值，土壤有机碳、全氮、C／N、硝态氮和有效磷的变化依次为31．628％、2．404％、-6．014％、90．370％和172．760％。由边际分析可知，长期施肥条件下土壤结构体分形维数的变化对土壤有效磷、硝态氮的影响最大。

Fractal characteristic of soil aggregates is an important index to describe soil structure. In this study, soil samples, collected from the 25-year long-term fertilizer experiment carried out on a manual loessial soil situated sub-humid farmland ecological system, were used to study the relationships among the fractal features, structures, and fertility of soil aggregates under different types of long-term fertilization. The results indicated that there were distinct differences among the fractal features of soil aggregates under different types of long-term fertilization, even though the soils are belonged to the same group which is Eum-Orthic Anthrosols. The fractal dimension values of soils in the seven treatments ranged from 2.4388 to 2.6363. The value for soils under the treatment of applying chemical fertilizer and stable manure together was the highest, and the lowest was the one without applying any fertilizer. The above results revealed that applying chemical fertilizer with organic matters together in a long-term had pronounce effects on the structure distribution of soil aggregates. The correlation analysis revealed that high significant positive correlation exited between the fractal dimensions of soil aggregate and 5-2 mm soil aggregate class, with correlation coefficient being 0.994. Moreover, there were significant positive correlations between the fractal dimensions of soil aggregates and concentrations of organic carbon and total nitrogen and nitrate nitrogen and available phosphorus in soils, while the correlation between carbon and nitrogen ratio （C/N） in soils and the fractal dimensions of soil aggregates was significant negative. Under different long-term fertilization, there were obvious differences among the marginal values of soil property change according to fractal dimensions of soil aggregates. With one unit of increment for the fractal dimension, the increment units for soil organic carbon, total nitrogen, C/N, nitrate nitrogen, and available phosphorus were 31.628% .2.404%. -6.014% .90.370% and 172.760% respectively. The marginal analysis indicated that the change of fractal dimension of soil aggregates influenced soil available phosphorus and nitrate nitrogen mostly.