The decreasing number of farm households in Japan is beginning to affect soil carbon and nitrogen balance. At both cool and warm sites, the soil C level was the lowest in the second year of the experiment, and thereafter, it gradually increased. The change in soil C concentration was negative at the warmer site; however, the content reached 119 g C m⁻² at the cooler site. Soil N showed a significant increase of 14.3 g N m⁻² from the first year to over 4 years at the cooler site. At the cooler site, less soil decomposition contributed to the retention of soil C and N, and the dominant deciduous woody plants increased the supplemental C and N content. Land-use management strategies involving conventional cultivation, abandonment and abandonment to recultivation did not affect the soil C and N balance for over 6 years. Fallow tillage to recultivation was less effective in retaining the C pool in the fifth year of the experiment, causing significantly lower soil C content (1.97 kg C m⁻²) than abandonment to recultivation (2.20 kg C m⁻²). Whereas the soil C content increased in the subsequent year (i.e. the sixth year), less productivity of recultivation crop (white mustard) contributed to a significant decrease in soil C, and abundant residue of winter wheat could recover the soil C and N in the subsequent year. The results suggest that agricultural abandonment can preserve soil C in cool regions and that the introduction of winter crops can maintain the C pool.

中文翻译：

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日本凉爽亚热带湿润气候下暂时停止耕作后的土壤碳平衡

日本农户数量的减少开始影响土壤碳氮平衡。在凉爽和温暖的地方，土壤C水平在试验的第二年最低，此后逐渐升高。温暖地区土壤C浓度变化为负；然而，在较冷的位置，含量达到了119 g C m ^{-2 。}土壤 N 显着增加 14.3 g N m ^-2从第一年到冷却器站点的 4 年以上。在较冷的地点，土壤分解较少有助于土壤C和N的保留，而优势落叶木本植物增加了补充C和N的含量。涉及常规耕作、弃耕和弃耕的土地利用管理策略在 6 年多的时间里没有影响土壤 C 和 N 平衡。在试验的第 5 年，休耕复垦在保留 C 池方面效果较差，导致土壤 C 含量（1.97 kg C m ^-2）显着低于弃耕复垦（2.20 kg C m ^{-2 ）}）。次年（即第 6 年）土壤 C 含量增加，复垦作物（白芥菜）产量降低导致土壤 C 显着下降，冬小麦的大量残茬可恢复土壤 C 和 N次年。结果表明，农业废弃可以保护凉爽地区的土壤碳，而冬季作物的引入可以维持碳库。