Effect of soil erosion on distribution of C and N in different particle size fractions of soil on the southern Loess Plateau

On the basis of the long-term soil erosion test,this paper studied the distribution of C and N in particle size fractions by the method of soil fractions as well as the relationship with sediment amount on dry land in order to study the declining of soil fertility and supervise local fertilization in southern Plateau Loess.The results showed that the contents of organic carbon and nitrogen in clay were highest,medium in silt,and lowest in sand.The organic carbon and nitrogen mainly distributed in silt and clay were lower than 50 μm,and respectively accounted for 97.07% and 85.25% of the soil total amount.The contents of organic carbon and nitrogen in particle size fractions decreased as sediment amount increased.The ratios of C/N in clay gradually increased,and gradually decreased in sand along with the increasing of the sediment amount.The sediment amount with content of organic C and N in clay,silt and sand of soil had an obvious or severe obvious linear relationship.Therefore,the plentiful loss of soil fine particle size fractions was an essential cause to reduce the fertility level on the Loess Plateau.