Spatial distribution of cultivated land quality and potential for capacity improvement of paddy fields in South China

In order to clarify the spatial distribution and promotion potential of paddy cultivated land quality in South China, and to provide a scientific basis for realizing high and stable rice yield in South China, based on the regional evaluation data of cultivated land quality in South China carried out by the Cultivated Land Quality Monitoring and Protection Center of the Ministry of Agriculture and Rural Affairs of the Perople’s Republic of China in 2017, this study analyzed the spatial distribution of paddy cultivated land quality and its corresponding relationship with productivity in South China. The stochastic forest model was used to identify the main limiting factors that affect the capacity improvement. The spatial distribution law of the quality grade of paddy field in South China was “high in the middle and low around”. The fitting result of semi-variance function showed that the quality grade of paddy field in South China was in moderate spatial correlation (R²=0.95), the highest in Guangdong (3.82) and the lowest in Hainan (5.32). Among the evaluation indexes of cultivated land quality in South China, there was a great difference in the spatial distribution of soil nutrient indexes, and the spatial distribution of soil total nitrogen and slowly available potassium showed a strong spatial correlation, with the spatial distribution law of “high in the west and low in the east” and “high in the north and low in the south”, respectively. The contents of soil organic matter, available phosphorus and available potassium showed moderate spatial distribution correlation, with a decreasing spatial distribution trend from west to east, east to west and north to south, respectively. The overall soil pH was weakly acidic (5.40), with moderate spatial distribution correlation. Soil physical properties, site conditions, soil management and soil health were better in the east and worse in the west. There was a significant positive correlation between the quality grade of paddy field and the overall rice yield in South China (R²=0.9140), and the rice yield increased rapidly at first and then tended to slow down with the improvement of cultivated land quality. There was a significant positive correlation between the quality grade of paddy land and the sustainable index of rice yield in South China (R²=0.9333). The importance analysis of stochastic forest model showed that soil available phosphorus content, irrigation capacity and soil organic matter content were the most important factors affecting rice yield in South China. Scenario simulation showed that if the quality grade of paddy land in South China is improved by 0.5, 1.0, 1.5 respectively, the yield will increase by 14.93%, 22.39% and 29.86%, which is equivalent to saving 317 700 hm², 563 500 hm² and 759 500 hm² of cultivated land. There is still great potential to improve the quality and production capacity of paddy farmland in South China. Improving the production capacity by improving the quality of cultivated land is of great significance to ensure food security and promote agricultural green production.