Abstract: 【Objective】 Soil basic productivity is the cornerstone of realizing high and stable yield for food crops. Defining the temporal change trends and spatial variation characteristics of cultivated land productivity for main food crops can provide important theoretical support for ensuring food security and improving cultivated land quality in China. 【Method】 In this study, based on the national long-term positioning monitoring network of cultivated land quality from 1988 to 2019, we selected the long-term monitoring data of the check area with non-fertilization treatment and the conventional area with farmers' fertilization treatment in the first 3-5 years since the establishment of each monitoring point. The temporal and spatial changes in yield of corn, rice and wheat and soil productivity contribution rates were analyzed in China. 【Result】 The results showed that in the past 30 years, the grain crops’ yield and soil productivity contribution rates showed an overall increasing trend with time, and the annual growth rate of crop yield showed the change law of non-fertilizer area < conventional area, rice < wheat < corn. The yield of maize, wheat and rice in the non-fertilizer area increased from 2 370 kg·hm^-2, 1 712 kg·hm^-2 and 3 111 kg·hm^-2 in 1988 to 4 852 kg·hm^-2, 3 258 kg·hm^-2 and 4 167 kg·hm^-2 in 2019, and increased by 104.7%, 90.2% and 34.0%, respectively. The yield of corn, wheat and rice in the conventional area increased from 5 356 kg·hm^-2, 3 296 kg·hm^-2 and 5 970 kg·hm^-2 in 1988 to 8 859 kg·hm^-2, 6 515kg·hm^-2 and 7 825kg·hm^-2, respectively, with the increment of 65.4%, 97.6% and 31.0%, respectively. The contribution rate of soil productivity for the three major food crops in China from 2015 to 2019 was 52.7%, which was significantly increased by 7.3% compared with 45.4% in 1988-1994. Among them, the contribution rate in maize was 54.3%, which was 12.2% higher than that of 42.1% in 1988-1994. The contribution rate in rice was 53.3%, which was 6.7% higher than that of 46.6% in 1988-1994. The soil productivity contribution rate in wheat increased with the year as a whole, and was lower than that in corn and rice as a whole. The spatial distribution of soil productivity contribution rate for the three major grain crops is quite different. The Northeast region and Huang-Huai-Hai region are higher, which are 56.5% and 54.1% respectively, followed by the Southwest region and South region, which are 53.7% and 52.9% respectively. Gan-Xin region and Qinghai-Tibet region are the lowest, only 38.7% and 40.4% respectively. The random forest model was used to rank the soil factors affecting the basic soil productivity contribution rate in the three major grain crop systems. Soil available potassium content, soil available phosphorus content and soil pH were the most key factors affecting the basic soil productivity contribution rate of corn, wheat and rice, respectively.【Conclusion】 Over the past 30 years, the soil basic productivity for three major grain crops in China has been continuously improved, but there are great differences among regions and the overall level is still low, which is far lower than that of developed countries in Europe and United States. Soil available potassium, organic matter content and soil bulk density are the most key factors affecting maize soil basic productivity contribution rate, and soil available phosphorus, available potassium and organic matter content are the most key factors affecting wheat soil basic productivity contribution rate. Soil pH, soil available phosphorus and organic matter content are the most key factors affecting the contribution rate of rice soil basic productivity.

Key words: rice, wheat, corn, crop yield, soil basic productivity