Long-Term Decomposition of Organic Materials with Different Carbon/Nitrogen Ratios

Abstract

Quantitative information on the decomposition rates and patterns of organic residues is fundamental for a better understanding of organic matter dynamics and nutrient cycling in soils. A laboratory incubation experiment was conducted under constant temperature (30°C) for 3 years to study changes in total carbon (C), total nitrogen (N), and C/N ratio of crop residues (rice, corn, alfalfa) and animal feces (pig, cattle) decomposing with and without soil. On average, rice, corn, and alfalfa residues lost a larger proportion of their original organic C than cattle and pig feces (82 vs. 70%). The presence of soil did not affect the total amount of organic C lost, with the exception of corn residues in which it increased it from 79 to 84%. Alfalfa residues, pig feces, and cattle feces lost a larger proportion of their total N than rice residues (38 vs. 15%). Both rice and corn residues showed an initial increase in total N, which may have been due to N immobilization from the soil and/or N fixation. Rice residues started losing total N after 15 months, whereas corn residues still showed an increase in total N after three years. The presence of soil decreased the loss of total N in alfalfa residue (32 vs. 48%) and pig feces (38 vs. 51%). The C/N ratios of all materials decreased during the decomposition and, with the exception of pig feces were similar to that of the soil by the end of the study (11:1 to 12:1). These results provide quantitative information that could be used to improve the management of residues and feces.

Keywords:

• Decomposition
• Carbon
• Nitrogen
• C/N ratio

Acknowledgments

Financial support by NKBRSF(G1999011804—03) is gratefully acknowledged. Shenyang Experimental Station of Ecology and Terrestrial Ecological Process Laboratory, Chinese Academy of Sciences, offered constant temperature lab and instruments are highly appreciated.