Carbon and nitrogen mineralization potential of biofuel crop (Jatropha curcas L.) residues in soil

Use and management of jatropha residue is currently an important global issue for attaining sustainability in biofuel production from Jatropha curcas on wastelands. Perhaps, knowledge about the decomposition characteristics and nutrient release pattern from jatropha residues amended soils are lacking. Thus, the objective of present research was to characterize the carbon (C) and nitrogen (N) mineralization of jatropha residues during decomposition in soil. The chemical composition of the residues, in terms of C, N, cellulose, hemicelluloses, lignin and phenolics contents were determined. Laboratory incubation studies were carried out with two soils (inside and outside-canopy soil of jatropha shrub) and four jatropha residues (1% w/w) amendments (cake, leaf, fruit shell or control soil only). The cumulative CO2 evolution of the added residues was in the magnitude of fruit shell>leaf>cake>control soil. Net C mineralized in soils were in the range of 46-50, 66-67 and 75-77% of C added by cake, leaf and fruit shell, respectively at the end of incubation study. Soils amended with leaf immobilized N during the first 64 days but subsequently released inorganic N. The addition of cake and fruit shell resulted in net N mineralization and net N immobilization, respectively throughout the incubation period. Cumulative N released by the end of incubation was in the order of cake>leaf>control>fruit shell. Net N mineralization in soils during the study was 75-92 and 21-27% of N added by cake and leaf, respectively whereas there was net N immobilization in fruit shell amended soil. Cumulative CO2 evolution as well as N mineralization during incubation were higher in inside-canopy soil compared with that of outside-canopy soil. Jatropha cake and leaf proved to be a potential source of mineral N, however leaf will take about 60-70 days as gestation period to mineralize the nitrogen. Similarly, leaf and fruit shell also exhibited a good potential of C mineralization.