Effects Of Harvest Residue Management And Land Use Change On Black Carbon And Black Nitrogen Of Soils

The effects of harvest residue management in forest plantations on soil carbon pool continue to receive attention,which are not only important to carbon balance,but also play important roles in sustaining forest productivity.Experiments in Xiayang forest farm,Nanping City of Fujian Province,China,were established to investigate the effects of harvest residue management on soil black carbon(BC),black nitrogen(BN)and soil organic matter structures.Meanwhile,we also studied the influences of land use change on the contents of soil orgainc carbon(SOC),total nitrogen(TN),BC and BN,soil samples were collected from the Altingia gralilipes native forest,Cunninghamia lanceolata plantation forest and Citrus aurantium orchards in Jianou City of Fujian Province.The major results were summarized as follows:At sampling years,the BC contents ranged from 2.99 to 3.70 g/kg under burning residue treatment,ranged from 3.52 to 4.36 g/kg under stem only harvest treatment,and ranged from 3.43 g/kg to 3.88 g/kg under whole tree harvest plus forest floor removal treatment.Soil BC stocks of three treatments were 3.24 t/hm2,3.87 t/hm2 and 3.38 t/hm2 respectively.The BN contents of three treatments ranged from 0.11 to 0.13 g/kg and the ranged stocks from 0.11 t/hm2 to 0.12 t/hm2.There were no significant differences in the contents and stocks of BC and BN at any sampling year for three treatments(P>0.05).The composition of SOM was similar for harvest residue managements by 13C NMR technique,the SOM of all soils was mainly composed of O-Alkyl-C,Alkyl-C and Aromatic-C.However harvest residue managements changed the proportion of different carbon species of the SOM.We applied 13C NMR technique and chemical oxidation method to quantify BC,and the BC contents were lower with 13C NMR than with chemical oxidation.SOC and TN contents decreased with soil depth increase in different land use types.In the whole soil layer(0?20 cm),the order of SOC and TN contents was Altingia gralilipes native forest>Cunninghamia lanceolata plantation forest>Citrus aurantium orchards.SOC and TN of natural forest were significantly higher than the other two types.The BC and BN contents of Altingia gralilipes native forest was highest and they also decreased with soil depth increase in different land use types.The proportion of BC to SOC was between 9.52?17.93%,and the proportion of BN to TN was between 5.19?10.22%.There was significant positive relationship between SOC and BC.Additionally,BC was mainly found in heavy fraction organic carbon using the density fractionation method.