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 * Corresponding author.M. Oda et al. 1173 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.
21 22A farmer grew crops by adding only organic material with a high C:N ratio (40) to the soil for 23 30 years. He focused on the role of carbon in increasing the number of microorganisms. This 24 idea was based on the concepts of 1) indirect crop management via microorganisms and 2) 25 providing carbon to microorganisms for energy. Here, we name this practice "carbon -driven 26 eco-agriculture" (CDEA). We determined the effect of CDEA on a laterite soil vegetable field 27 in Sao Paulo for 4 years. The yield exceeded the national average. Soil aggregates formed to 28 29 cm thickness, and the microbial activity was one order of magnitude higher than that in a 29 conventional control field. The output/input ratios of carbon and nitrogen were 1.88 -2.35 and 30 3.58-6.00, respectively, indicating a sustainable system for these elements. Incorporating 31 high-C:N-ratio (>20) organic material results in nitrogen deficiency.
Certain farms in Japan, namely unfertilised farms (UFs), have been able to maintain high productivity for over 40 years without applying fertilisers or composts. This study aimed to characterise the physicochemical, biological and micromorphological properties of soil in UFs compared with control farms in Eniwa and Nariita and to identify characteristics that are associated with crop productivity. In UFs, no plough pan was observed. The thickness of the effective soil depth (ESD) of UFs was greater than that of CFs. The concentrations of soil organic carbon, total nitrogen and nitrate-nitrogen in ESD of UFs were higher than those in ESD of CFs. Soil microstructure observations indicated the strong development of a granular microstructure with large amounts of void space and a high fractal dimension in both surface and subsoil horizons of UFs. Dry yield had a strong correlation with ESD thickness and fractal dimension of voids. Thus, the management of unfertilised cultivation promoted the development of soil aggregation in both A and B horizons. The increase in ESD, soil pore spaces and complexity with the development of subsoil structure improved the productivity of unfertilised cultivation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.