Responses of carbon and potassium contents in soil aggregates to the duration of taro-rice rotation

The taro (Colocasiaes culenta)-rice (Oryza sativa) rotation has been rapidly developed in the northeastern area of Jiangxi Province in recent years.However, the influence of high organic fertilizer input and continuous straw returning on soil aggregate carbon and potassium (K) is not clear.Thus, it is essential to study the distribution of carbon and K contents in soil aggregates under taro-rice rotation with different cultivation years, which can provide theoretical basis for optimal fertilization in taro-rice rotation system.In 2020, we selected taro-rice rotation for one year, three years, five years and ten years as the treatments, and one season of rice cultivation as a control (CK) in Hufang Town of Yanshan County in Shangrao City of Jiangxi Province.We determined the soil fertility, aggregate components and their organic carbon and potassium contents; further analyzed the correlation between the contents of organic carbon and available K in each aggregate component.The results showed that taro-rice rotation alleviated soil acidification, and greatly improved soil fertility with increasing rotation years.Rotation years changed the proportion of soil aggregates, and the proportion of large aggregates (>2 mm) increased with increasing rotation years.The proportion of large aggregates (>2 mm) in 5-year rotation treatment was significantly higher than that of CK treatment.The organic carbon contents in the >2 mm, 0.25~2 mm, 0.053~0.25 mm aggregates increased with increasing rotation years, and reached the maximum value at 10-year rotation, which was significantly increased by 18.6%, 40.9% and 29.9% relative than that of CK treatment, respectively.The total K contents in the >2 mm aggregate increased significantly by 13.6% in 5-year rotation than that of CK.With increasing rotation years, total K contents continued to increase, but the increased magnitude became smaller.Compared with CK, the available K contents in the >2 mm aggregate in 3-year rotation treatment significantly increased by 2.24 fold.There was a significantly positive correlation between organic carbon and available K content in > 2 mm aggregates (R²=0.93, P < 0.05).The slope of linear equation suggested that the available potassium content increased by 3.30 mg · kg^-1 when the organic carbon increased by 0.10 g · kg^-1 in > 2mm aggregates.In conclusion, taro-rice rotation improves soil fertility and increases the proportion of organic carbon in large aggregates, thus facilitating soil K accumulation to meet crop growth requirement.