Effects of long-term fertilization on soil black carbon accumulation in Lou soils

Effects of fertilization on content and accumulation of soil black carbon were investigated based on the 20year longterm experiment on Lou soil. There were four fertilizer treatments, the control without applying any fertilizers (CK), single application of chemical fertilizer (NPK), straw returning combined with chemical fertilizers (SNKP) and organic manure combined with chemical fertilizers (M1NPK, M2NPK). Results show that compared with the CK, the single application of chemical fertilizer has no effect on the content and accumulation of black carbon, the treatments of organic manure combined with chemical fertilizers (M1NPK, M2NPK) significantly increase the contents of black carbon in the 0-20 cm soil depths and the black carbon contents are increased by 108% and 134% in the 0-5 cm soil depths and 164% and 176% in the 5-10 cm soil depths respectively, and the accumulations of black carbon in soil profiles are increased by 1.51 and 1.55 times respectively under M1NPK and M2NPK treatments. The black carbon contents in top soils are increased under the treatment of SNPK, but the increases are relatively small compared with the manure application. Effects of the fertilization on the black carbon mainly occur in the top soils, while the black carbon contents in the deep soils are less affected.