Extraction of oils from castor bean (Ricinus communis L.) and Jatropha curcas L. 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, México, were amended with seed cake of both plants while CO 2 , CH 4 and N 2 O 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 CO 2 emission 2.5-times, N 2 O 12.6-times and CH 4 18.4-times compared to the unamended soil, while RSC CO 2 emission 2.1-times, N 2 O 21.3-times and CH 4 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 CO 2 , CH 4 and N 2 O emission and mineral N in soil, without inhibiting soil microbial activity.

Cultivation of plants, such as castor bean (Ricinus communis L.) or Jatropha curcas L. is set to increase in future as their seeds are used to extract oil for biofuel production. Ricinus communis seed cake (RSC) and J. curcas seed cake (JSC) were applied to soil cultivated with wheat (Triticum spp. L.) while plant growth and emissions of the greenhouse gases, CO 2 , CH 4 and N 2 O were monitored. Application of RSC or JSC had no significant effect development of the wheat plants. Emissions of CO 2 and N 2 O increased in soil amended with JSC or RSC, especially when larger amounts were applied, but had no effect on emissions of CH 4 . It was found that application of seed cakes increased emissions of CO 2 and N 2 O, but did not stimulate plant growth.Keywords: biofuel; decomposition of seed cake; emissions of CO 2 , CH 4 and N 2 O; mineral N; soil characteristics V.M. Ruíz-Valdiviezo, Á. Aguilar-Chávez and M.R. Cárdenas-Aquino contributed equally to the experiment.