Objective  Soil exchangeable calcium (Ca) is an important indicator to evaluate the extent of soil Ca deficiency. The objective of this study was to investigate the spatial distribution characteristics and influencing factors of exchangeable Ca of arable soils in Fujian Province, and to provide a reference basis for the soil Ca fertilizer management.

  Method  The soil of farmland in Fujian Province was took as the research object. The data of 1900 soil monitoring sites in Fujian Province during 2016 to 2019 were collected to quantify the effects of different natural conditions (altitude and mean annual precipitation), soil properties (soil exchangeable magnesium, soil available potassium, pH, soil organic matter, soil type, and soil texture), and crop systems on soil exchangeable Ca. Besides, the relative importance of these influencing factors to soil exchangeable Ca was clarified by random forest model (RF).

  Result  The soil exchangeable Ca concentration was 519 mg kg⁻¹ in average, lower than 400 mg kg⁻¹ in 49.3% of the area, and between 400 ~ 800 mg kg⁻¹ in 31.6% of the area. The increase of soil exchangeable magnesium concentration, pH and soil organic matter significantly increased soil exchangeable Ca concentration, while the increase of altitude significantly decreased soil exchangeable Ca concentration. The exchangeable Ca concentrations of paddy soil and latosol soil were 650 mg kg⁻¹ and 632 mg kg⁻¹, which were significantly higher than that of yellow soil. The soil exchangeable Ca concentrations of rice vegetable rotation system and vegetable system were significantly higher than those of other cropping systems. In addition, RF analysis indicated that the exchangeable magnesium was the most important factor impacting the exchangeable Ca concentration, followed by altitude, soil pH and crop type, while the mean annual precipitation, soil texture, soil available potassium, soil type and soil organic matter content showed little influence.

  Conclusion  Overall, the soil exchangeable Ca concentrations in Fujian Province were generally low, which is suggested to be improved with application of more Ca fertilizers. In Ca fertilizer application, local climatic conditions, soil properties and crop types should be fully considered to improve Ca utilization efficiency and promote crop yield and quality.