Soil quality assessment of cropland in China and its relationships with climate and topography

Assessing soil quality (SQ) of cropland is fundamental for food security and sustainable land management. However, there is limited information regarding SQ assessment on a national scale, which is vital to answer important SQ-related questions in quantitative terms on that scale. Here, the SQ of cropland in China was assessed by constructing a minimum data set (MDS) from 23 soil physicochemical properties based on principal component analysis. The interaction roles and relative contributions of climate and topography on SQ was evaluated by a structural equation model. The MDS comprised eight indicators: proportion of silt, bulk density, total phosphorus, total potassium, available nitrogen, exchangeable calcium, chlorite, and vermiculite. The soil quality index (SQI) varied from 0.245 to 0.705 and showed a clear pattern of decreasing quality from the north to the south of the country. Of the total cropland area in China, the largest share (27.91%) was of soils of high quality, followed by those of moderate quality (24.63%), low quality (20.37%), very high quality (14.18%), and very low quality (12.91%). The north and the south differed significantly in terms of total potassium, exchangeable calcium, chlorite, and vermiculite, which are the four most important indicators of SQ. Climate and elevation explained about 2.2%–30.1% of the variation in SQ on the national and regional scales. These findings suggest that croplands in southern China will benefit from potassium and calcium fertilizers, which will contribute to enhance food security and promote sustainable land management in China.