Soil organic carbon and aggregation under poplar based agroforestry system in relation to tree age and soil type

The poplar based agroforestry system improves aggregation of soil through huge amounts of organic matter in the form of leaf biomass. The extent of improvement may be affected by the age of the poplar trees and the soil type. The surface and subsurface soil samples from agroforestry and adjoining non-agroforestry sites with different years of poplar plantation (1, 3 and 6 years) and varying soil textures (loamy sand and sandy clay) were analyzed for soil organic carbon, its sequestration and aggregate size distribution. The average soil organic carbon increased from 0.36 in sole crop to 0.66% in agroforestry soils. The increase was higher in loamy sand than sandy clay. The soil organic carbon increased with increase in tree age. The soils under agroforestry had 2.9-4.8 Mg ha(-1) higher soil organic carbon than in sole crop. The poplar trees could sequester higher soil organic carbon in 0-30 cm profile during the first year of their plantation (6.07 Mg ha(-1) year(-1)) than the subsequent years (1.95-2.63 Mg ha(-1) year(-1)). The sandy clay could sequester higher carbon (2.85 Mg ha(-1) year(-1)) than in loamy sand (2.32 Mg ha(-1) year(-1)). The mean weight diameter (MWD) of soil aggregates increased by 3.2, 7.3 and 13.3 times in soils with 1, 3 and 6 years plantation, respectively from that in sole crop. The increase in MWD with agroforestry was higher in loamy sand than sandy clay soil. The water stable aggregates (WSA > 0.25 mm) increased by 14.4, 32.6 and 56.9 times in soils with 1, 3 and 6 years plantation, respectively, from that in sole crop. The WSA > 0.25 mm were 6.02 times higher in loamy sand and 2.2 times in sandy clay than in sole crop soils.