Tracing carbon and nitrogen flow from maize through goat to manure compost: A dual label (13C and 15N) study

Integrated crop-livestock systems and organic manure application are vital strategies for sustainable agriculture. Understanding carbon (C) and nitrogen (N) cycling from crops, through animal digestion to manure, and subsequently to soil is essential. However, studies on these processes remain scarce due to high costs and technical complexities associated with preparing dual-labeled (¹³C and ¹⁵N) manure, which deter researchers from conducting such experiments. Our study pioneers dual-labeled manure preparation and provides a methodological framework for simultaneously tracing C and N cycling from feedstuffs to manure in long-term nutrient cycling research. Key findings include the distribution of ¹³C and ¹⁵N across different maize components (kernel, cob, leaves, stalk, and root), and goat manure, and compost. The study revealed the transformation and recovery of C and N from maize to manure. For instance, 31.7% of manure C and 27.3% of manure N originated from maize feed, with 11.8% of feed ¹³C and 28.6% of feed ¹⁵N recovered in manure, and 16.5% and 25.8% recovered in compost, respectively. Composting enhanced C retention and stabilized N, improving nutrient cycling efficiency. While no correlation between ¹³C and ¹⁵N was observed in maize tissues, a strong linear relationship (R² = 0.9908, p < 0.001) was identified in goat manure during a 10-day feeding period. These findings provide a foundation for future studies tracing C and N cycling from manure compost, invaluable for refining C and N cycling models. Future studies should extend the tracing period across diverse crop-livestock systems to validate these findings.