Emission of CO2, CH4 and N2O and dynamics of mineral N in soils amended with castor bean (Ricinus communis L.) and pinon (Jatropha curcas L.) seed cake

Extraction of oils from castor bean and Jatropha curcas to produce biofuel is set to increase. The produced seed cake could be applied to soil as it is nutrient rich, but might affect soil functioning. Seven soils from Chiapas, Mexico, were amended with seed cake of both plants while CO2, CH4 and N2O emissions and mineral N concentrations were monitored in an aerobic incubation. The concentration of phorbol esters in the J. curcas seed cake (JSC) was 0.993 mg/g while no ricin was detected in the R. communis seed cake (RSC). Application of JSC increased CO2 emission 2.5-times, N2O 12.6-times and CH4 18.4-times compared to the unamended soil, while RSC CO2 emission 2.1-times, N2O 21.3-times and CH4 2.3-times. On average, 66% of the 88 mg organic N added with JSC was mineralized and 83% of the 101 mg organic N of the RSC within 56 days. It was found that J. curcas and castor bean seed cake increased CO2, CH4 and N2O emission and mineral N in soil, without inhibiting soil microbial activity.