Abstract:

Through field investigation and laboratory analysis, distribution characteristics of soil microaggregates and organic carbon under different tea plantation age were studied.The results showed as follows.(1) The tea garden soil microaggregate concentrations decrease with the decrease in the particle size in general, indicating that tea garden soil in the study area has stronger ability of protecting fertilizer.In the upper (0-20 cm) soil layer,along with the extending length of planting tea,concentrations of microaggregates in the sizes of > 005 mm，001-0005 mm and < 0001 mm  show a “∧” type changing pattern，concentrations of the remaining fraction present an increasing trend.In the lower soil layer (20-40 cm)，graded levels of microaggregates in the sizes of > 005 mm and 005-001 mm varied obviously with plant tea length extended，while concentrations of the remaining three grades of microaggregates  remain stable with increases in years planting tea.(2) Tea garden soil organic carbon concentration with microaggregate fraction increases with the decrease in the microaggregate concentrations.This is because the soil microaggregate fraction is smaller，the specific surface area is larger，and the organic carbon adsorption ability is stronger.Along with the increase in planting tea fixed number of year，the organic carbon concentration in the microaggregate graded increases.This is mainly due to fact that in the natural soil after planting tea，a lot of old leaves return soil，bringing large amounts of carbon sources.Total organic carbon concentrations of different fixed number of year of the tea garden soil decrease with the increase in soil depth，mainly because of the mobility of the soil organic matter and organic matter source of the differences.(3) Microaggregate contribution to > 005 mm of soil organic carbon fraction is given priority to，granule grades of 005-001 mm，0005-0001 mm grade at least.With increasing years of planting tea，microaggregates in the size of > 005 mm decrease their contribution rate of soil organic carbon，microaggregates in the size of 005-001 mm increase their contribution of soil organic carbon，whereas microaggregates of the other particle sizes present a changing trend of first increases and then reach a maximum in 21-23 years tea，suggesting that in the 21-23 years tea,31-33 years of soil microaggregates structure is gradually stable