The Effect Of Long-Term Fertilization And Land Use Pattern On Red Soil Aggregate Stability

Soil aggregate is a basic structural unit of soil, factors which influencing the stability and formation of soil aggregate including internal aspects such as environment, physicochemical properties of soil, especially the cementation of binding materials. External factors refer to human activities including land use patterns and fertilizations. There’s a large area of red soil widely distributed in southern China which is an important production base for grain and vegetable oil. We took23-year long-term red soil in Qiyang as the research object of fertilizations which effecting on soil aggregate, including fallow land (LH), control treatments (CK), single nitrogen (N), chemical NPK fertilizers (NPK) and chemical fertilizers plus pig manure (NPKM). We took18-year long-term red soil in Taoyuan as the research object of land use patterns which effecting on soil aggregate, including natural recovery (NR), traditional use (TU), crop rotation (CR) and artificial forest (AF). We came to the following conclusions through the analysis of the relationships among soil organic matter, iron oxide, ultrasonic broken and soil aggregate stability:(1) Both fertilization and land use changed soil pH, N led to soil acidification, pH reduced1.76units; The balance using of chemical fertilizers relatively reduced the degree of acidification, pH decreased1.76units; pH changed from5.70to5.86with NPKM. Under four different land use patterns, NR had the lowest pH (pH=4.58), there was no significant effect on soil pH of other three land utilization types. The results of dry sieving and wet sieving showed that NPKM kept good soil structure, then a balance applied of chemical fertilizers, aggregate stability of CK and N was the weakest. Content of soil aggregate which was bigger than0.25mm following the order presented below: LH (74.4%)> NPKM (58.34%)> NPK (35.85%)> CK (24.92%)> N (23.36%). Traditional use of land in Taoyuan formed the best soil structure, while crop rotation led to the worst soil structure. The content of water stability aggregate (>0.25mm) following as TU (74.98%)> AF (53.80%)≥NR (52.90%)> CR (48.90%).(2) The content SOM had the same change rule as pH influenced by fertilization. Crop rotation improved soil quality because of extra fertilization and biological return (SOM=27.58g/kg). The content of SOM under TU pattern was higher than AF and NR. Both fertilizations and land use patterns resulted in the redistribution of SOM in soil aggregate, SOM content increased with the size of soil aggregate rised. The distribution of Fed in red soil had the same trend as SOM, application of organic fertilizer promoted the conversion from Fed to Feo, correlation was significant at the0.01level (R2=0.893**, n=8). Different forms of iron oxide with different distribution showed different microenvironment. It was easier for the formation of Feo in microaggregate.(3) L (TU) of macroaggregate and microaggregate was334.73and228.84J·g-1respectively, it had the strongest ability to resist external forces. LH in Qiyang had the highest energy to prevent damaging because of without human disturbance and grew plants all the year round freely, each size of the aggregate had the energy of374.03J·g-1and310.13J·g-1. The mechanical stability of aggregate reduced from the analysis of ultrasonic test after tillage management. Single nitrogen had the weakest ability to resist external force disrupting, energy of it decreased about2/3compared with LH. NPK was the best treatment to protect soil mechanical stability, energy of it was about two-thirds of LH. We found that macroaggreate (2-0.25mm) had better ability to resist damaging than microaggreate (0.25-0.053mm).(4) Chemical grouting agent on water stable aggregate ability to resist external force (L) and time (T) varied in different types of land management: Correlation was significant at the0.01level of L and T (R2=0.697**, n=18), they had positive correlation with SOM respectively (R2=0.483*and0.499*, n=18). Both Fed and Fed-Feo controlled the value of T, each of the correlation coefficient was0.759*and0.754*(n=8). The effect of chemical cementing agent was hided under different land management. We found that reduce external disturbance make the influence of chemical cementing material more complex in soil aggregate through the analyze of different land management.