Effect Of Planting-year Of Tea On Composition Of Soil Aggregate And Fractions Of Organic Carbon

In this research, the age of planting tea of12-15,20-22,30-33and50years in Wan Li ecological tea plantation of Zhongfeng Village, Mingshan County, Sichuan Province are the research objects to have determination and analysis on soil aggregate components and organic carbon fractions so as to figure out the physical structures that can be improved by the terms of planting tea in the soil of tea plantation. The target of this is to offer the theoretical basis on enhancing the water retention, soil fertility, and promoting the sustainable utilization of the soil in the tea plantation. Meanwhile, the target of this research is to offer particular scientific basis to the further study on carbon source and carbon sink effect of the soil, increasing the carbon sequestration in the tea plantation. The research results indicate:(1) The non-water-stable aggregates that have a partical size greater than5mm occupy the largest proportion for the soil that has different age of planting tea, the aggregates that have a partical size of5-2mm take the second place, and the proportion of the ones that have a partical size between0.5-0.25mm are in the last place. The water-stable aggregate that have a partical size greater than5mm and smaller than0.25mm occupy the largest proportion, the ones that have a partical size between1-0.5mm or between5-2mm take the second place, and the ones between2-lmm are in the last place. However, micro-aggregates that have a partical size greater than0.05mm are in the lead, the ones between0.05-0.01mm take the second place, and the ones small than0.001mm are in the last place. And the non-water-stable aggregates that have a partical size greater than5mm and water-stable aggregates greater than0.25mm occupy a proportion between50%～80%. The components of micro-aggregates greater than0.01mm are in the lead. The proportion of non-water-stable aggregates and water-stable aggregates that have partical size greater than5mm goes up and then goes down as the growth of the age of planting tea. The proportion is the largest in the term of planting tea that is20years, and the distribution of the proportions to the five aggregates that have a partical size smaller than5mm is in the opposite. As for different age of planting tea, the proportion is the largest when the value of MWD, GMD and D of non-water-stable aggregate and water-stable aggregate are in the term of planting tea between20to22years, the D value is the smallest to fractal, and the MWD, GMD and D values have significant difference in different age of planting tea.(2) As the partical size of non-water-stable aggregate decreases in the soil of tea plantation, the content of TOC, LOC, POC, WSOC and PMC increases. Basically, the maximum value concentrates on the aggregates that have a partical size smaller than0.25mm and0.5-0.25mm. However, the content of MBC increases and then decreases as the partical size decreases. And the aggregate that has the maximum value between5-2mm, that is to say, the non-water-stable aggregate that has a small partical size has a large content of organic carbon fraction. The proportion of organic carbon of each component to the total organic carbon in non-water-stable aggregate decreases as the partical size decreases. As the partical size of water-stable aggregate in the soil of tea decreases, the content of TOC, LOC and POC and MBC and PMC tends to decrease, and the content of WSOC increases. That is to say, the content of organic carbon fraction of water-stable aggregate that has a big partical size is very large.(3) As the age of planting tea increase, the content of TOC of non-waterstable aggregate in the soil of tea plantation increases, and the content of LOC and POC has the variation trend of decreasing and then increasing. Content that is in the term between20and22years is the lowest. Content of WSOC, PMC and MBC has the variation trend of increasing and then decreasing. Content that is in the term between30and33years is the highest. The proportion of organic carbon to the total organic carbon in each component of waterstable aggregate tends to decrease as the term of planting tea increases. As the term of planting tea increases, the content of TOC, LOC, POC, MBC, WSOC and PMC tends to increase and then decrease as the term of planting tea increases, maximum in the term between20and22years, minimum in the term more than50years.(4) The content of carbon fractions of the soil layer which is0-20cm is greater than it of the soil layer that is20-40cm in the non-waterstable aggregate of soil of the tea plantation. Proportion of organic carbon of each component of the soil layer that is20-40cm is greater than it of the soil layer that is0-20cm to the TOC in the soil aggregate. And the content of carbon fractions of the soil layer that is20-40cm is greater than it of the soil layer that is0-20cm to the total organic carbon in the waterstable aggregate of soil.