Modified framework to reflect contribution of soil storage in emergy synthesis under different agricultural practices at farm level

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Emergy synthesis (ES) is a powerful tool to assess the sustainability of agricultural eco-economic system. However, based on the traditional ES framework (TES), the sustainability of cropping system under different agricultural practices could not be reasonably compared, because the real contribution of soil storage was not rationally calculated while only the emergy input derived from topsoil loss was considered. This study proposed a modified ES framework (MES) based on the logic of soil nutrient balance to reflect the contribution of soil storage in the ES under different agricultural practices at farm level. A field experiment of sweet maize cropping system under different fertilization practices in South China was took as a case to compare the emergy-based indices under the TES and MES frameworks. According to the MES framework, the changes of soil nutrients including the SOM, N, P and K in the farming system were considered. The emergy flows of them were calculated by involving the measured data on field. The results of emergy-based indices demonstrated that the MES approach could reflect the difference of cropping system under different agricultural practices at farm level. Meanwhile, the results also indicated that the application of chemical fertilizer with biochar was the best practice for improving the sustainability of sweet maize production system in South China based on the MES approach. This study was expected to promote the application of the ES method on the sustainability assessment of agricultural system at the farm level.