The relative isotopic abundance (δ13C, δ15N) during composting of agricultural wastes in relation to compost quality and feedstock

Variations in the relative isotopic abundance of C and N (δ13C and δ15N) were measured during the composting of different agricultural wastes using bench-scale bioreactors. Different mixtures of agricultural wastes (horse bedding manure + legume residues; dairy manure + jatropha mill cake; dairy manure + sugarcane residues; dairy manure alone) were used for aerobic–thermophilic composting. No significant differences were found between the δ13C values of the feedstock and the final compost, except for dairy manure + sugarcane residues (from initial ratio of −13.6 ± 0.2 ‰ to final ratio of −14.4 ± 0.2 ‰). δ15N values increased significantly in composts of horse bedding manure + legumes residues (from initial ratio of +5.9 ± 0.1 ‰ to final ratio of +8.2 ± 0.5 ‰) and dairy manure + jatropha mill cake (from initial ratio of +9.5 ± 0.2 ‰ to final ratio of +12.8 ± 0.7 ‰) and was related to the total N loss (mass balance). δ13C can be used to differentiate composts from different feedstock (e.g. C3 or C4 sources). The quantitative relationship between N loss and δ15N variation should be determined.

本研究借助台式生物反应器（bench-scale bioreactors），针对不同配比的农业废弃物好氧高温堆肥过程，测定了碳、氮相对同位素丰度（δ¹³C与δ¹⁵N）的动态变化。实验设置了4组废弃物混合体系：马垫料粪便与豆科植物残体复配、奶牛粪便与麻疯树饼粕复配、奶牛粪便与甘蔗渣复配，以及单独奶牛粪便。结果表明，除奶牛粪便+甘蔗渣组（初始比值为-13.6 ± 0.2 ‰，最终比值为-14.4 ± 0.2 ‰）外，其余各组原料与最终堆肥的δ¹³C值均无显著差异。马垫料粪便+豆科植物残体组（初始比值+5.9 ± 0.1 ‰，最终比值+8.2 ± 0.5 ‰）与奶牛粪便+麻疯树饼粕组（初始比值+9.5 ± 0.2 ‰，最终比值+12.8 ± 0.7 ‰）的堆肥产物δ¹⁵N值均显著升高，且该变化与总氮损失（通过质量平衡法核算）密切相关。δ¹³C可用于区分不同原料来源的堆肥（如C3或C4植物源）。后续需明确氮损失与δ¹⁵N变化之间的定量关联。