Abstract
It is known that cropping causes soil carbon loss, which is a critical issue, especially in tropical agriculture. Nitrogen input generally increases net primary production but does not increase soil carbon content because nitrogen input enhances soil organic carbon mineralization by microorganisms. A farmer conducted a trial in which he applied material with a high carbon:nitrogen (C:N) ratio without additional nitrogen fertilizer, and achieved a higher productivity than that of conventional farms. Based on his results, we conducted a survey to evaluate the effects of high C:N ratio organic material on the productivity, soil profile, microbial activity, and carbon and nitrogen balance of soil. Results demonstrate that high C:N ratio organic material enhanced the formation of the soil A horizon and increased soil carbon and nitrogen content. Approximately, 15 - 20 t·ha-1·crop-1 of fresh waste mushroom bed was applied to 15 crops over 4.5 years, and the total input of carbon and nitrogen were 5014 and 129 g·m-2, respectively. The soil nitrate nitrogen concentration was the same as that of the neighboring forest soil, which was lower than the standard limit for conventional agriculture; however, the average productivity of crops was approximately four times that of the national average. The soil Ap horizon increased in thickness by 7 cm, and aggregates reached a thickness of 29 cm in 4.5 years. The output/input ratios of total soil nitrogen and carbon were approximately 2.68 - 6.00 and 1.30 - 2.35, respectively, indicating that this method will maintain the carbon and nitrogen balance of the system. The observed soil microbial activity was one order of magnitude higher than that of a fallow field. The results indicate that this agricultural method remediates soil degradation, and improves food production.
Highlights
Soil carbon stocks decline by an average of 42% after land is converted from native forest to crops and by 59% after conversion of pasture to crops [1]
When organic material with a high C:N ratio is added to the soil, soil microorganisms use the carbon as a substrate and multiply simultaneously using the available soil nitrogen, thereby decreasing the nitrogen content of the soil [12]
We found that inputting high C:N ratio organic material without additional nitrogen drastically increased the soil nitrogen content
Summary
Soil carbon stocks decline by an average of 42% after land is converted from native forest to crops and by 59% after conversion of pasture to crops [1]. It has been reported that differences in crop carbon inputs are positively related to soil organic carbon stock differences [8]. When organic material with a high C:N ratio is added to the soil, soil microorganisms use the carbon as a substrate and multiply simultaneously using the available soil nitrogen, thereby decreasing the nitrogen content of the soil [12]. To prevent this depletion, materials with a low C:N ratio (
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