Increase of Organic Carbon Accumulation in Deep Soil of Paddy Fields by Long Term Continuous Cropping of Zizania latifolia
To understand the changes of organic carbon pool and its components in paddy soils after long-term continuous cropping of Zizania latifolia,six groups of farmlands with the same soil type,varying in Zizania latifolia plantation years of 0(control),2-5,5-10,10-20,20-30 and 30-35,were selected,and soil samples of 0-20,20-40,40-60 and 60-80 cm layers were collected.Soil organic carbon,different stable forms of organic carbon and microbial biomass carbon were analyzed.The results showed that with the increase of the plantation time of Zizania latifolia,the soil bulk density decreased gradually from the upper layer to the lower layer,the total amount of soil organic carbon,highly active organic carbon,moderately active organic carbon,low active organic carbon,inert organic carbon and microbial biomass carbon in each of soil layers gradually increased,with the most obvious increase in 20-40 and 40-60 cm soil layers.Meanwhile,the proportion of highly active organic carbon in deep soil increased significantly.The storage proportion of total organic carbon and various forms of organic carbon of 20-80 cm soil layers in all of 0-80 cm soil layers also increased gradually,showing the characteristics of organic carbon accumulation in deep soil.The main reasons for the rapid accumulation of organic carbon and the increase of organic carbon activity in the deep soil of farmland planted with Zizania latifolia were the gradual disappearance of the plough pan and the formation of the soft paste layer caused by deep tillage,long-term flooding and frequent human trampling in the field during the production of Zizania latifolia.
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