Soil basic productivity is the cornerstone of realizing high and stable yield for food crops. The temporal change trends and spatial variation characteristics of cultivated land productivity for main food crops were defined, so as to provide the important theoretical support for ensuring food security and improve cultivated land quality in China.

In this study, based on the national long-term positioning monitoring network of cultivated land quality from 1988 to 2019, the long-term monitoring data of the check area were selected 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 maize, rice and wheat and soil productivity contribution rates were analyzed in China.

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 < maize. The yield of maize, wheat and rice in the non-fertilizer area increased from 2 370, 1 712 and 3 111 kg·hm^-2 in 1988 to 4 852, 3 258 and 4 167 kg·hm^-2 in 2019, respectively, and increased by 104.7%, 90.2% and 34.0%, respectively. The yield of maize, wheat and rice in the conventional area increased from 5 356, 3 296 and 5 970 kg·hm^-2 in 1988 to 8 859, 6 515 and 7 825 kg·hm^-2 in 2019, 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 from maize was 54.3%, which was 12.2% higher than that of 42.1% in 1988-1994. The contribution rate from rice was 53.3%, which was 6.7% higher than that of 46.6% in 1988-1994. The soil productivity contribution rate from wheat increased with the year as a whole, and was lower than that in maize and rice as a whole. The spatial distribution of soil productivity contribution rate for the three major grain crops was quite different. The Northeast region and Yellow River and Huaihai region were higher, which were 56.5% and 54.1%, respectively, followed by the Southwest region and South region, which were 53.7% and 52.9%, respectively. Gan Xin region and Qinghai-Tibet region were 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. Among them, soil available potassium, organic matter content and soil bulk density were the key factors affecting the spatial distribution of maize basic soil fertility contribution rate; soil available phosphorus, available potassium and organic matter content were the key factors affecting the spatial distribution of wheat basic soil fertility contribution rate; soil pH, soil available phosphorus and organic matter content were the key factors affecting the spatial distribution of rice basic soil fertility contribution rate.

Over the past 30 years, the soil basic productivity for three major grain crops in China has been continuously improved, but there were great differences among regions and the overall level was still low, which was far lower than that of developed countries in Europe and United States. Soil available potassium content, soil available phosphorus content and soil pH are the most key factors affecting the spatial distribution of basic soil fertility contribution rate of maize, wheat and rice, respectively.