To identify the soil carbon stock changes from croplands/grasslands to forestlands in Japan, we compared the soil carbon stock of a cropland/grassland with that of an adjacent forestland at 22 different sites. With respect to a 0–30-cm depth basis, the soil carbon stock in the cropland/grassland was the same as that in the forestland; however, it was less than that in the forestland when an equivalent mass approach was used. The ratio of the soil carbon stock in the forestland to that in the cropland/grassland was 1.11 on average, which is comparable with previous mass-corrected paired sampling studies. The ratio was affected by two factors: tree age and current vegetation. Mean annual temperature, mean annual precipitation, phosphate absorption coefficient, litter quantity, and former land use did not affect the ratio. According to a comparison with the results of a paired study for deforestation, the application of the reciprocal of the soil carbon stock ratio of deforestation to the ratio of afforestation was slightly overestimated. Further studies are necessary to establish a general conclusion. Some previous studies, including those involving non-mass-corrected data, are possibly biased, and more studies using the paired sampling method with equivalent mass basis must be conducted to provide the general factor for soil carbon stock change in the future.

为了确定日本从农田/草地到林地的土壤碳储量变化，我们比较了农田/草地与相邻林地在22个不同地点的土壤碳储量。就0–30厘米深度而言，耕地/草地的土壤碳储量与林地的碳储量相同。但是，当采用等效质量方法时，它比林地中的要少。林地与农田/草地的土壤碳储量之比平均为1.11，与先前的质量校正配对采样研究相当。该比率受两个因素影响：树木年龄和当前植被。年平均温度，年平均降水量，磷酸盐吸收系数，凋落物数量和以前的土地使用均不影响该比例。与对森林砍伐的成对研究结果进行比较后，对森林砍伐的土壤碳储量比与森林造林比率的倒数的应用被高估了。有必要进行进一步的研究以建立一个一般性的结论。某些先前的研究，包括那些涉及未经质量校正的数据的研究，可能会产生偏差，并且必须进行使用等效质量基准的配对采样方法进行更多的研究，以提供未来土壤碳库变化的一般因素。