Spatial and Temporal Distributions of Soil Available Phosphorus in Wheat-Cotton Double-Cropping Systems

[Objective] Here, the spatial and temporal distributions of soil available phosphorus (AP) were investigated during cotton growth stages in wheat-cotton double-cropping systems in northern Henan, China. [Method] Using the spatial grid sampling and geo-statistical analysis methods, we analyzed the spatial and temporal distributions of soil AP in a cotton monoculture, wheat-cotton 3-1 intercropping system (3-1) and wheat-cotton 6-2 intercropping system (6-2) during the wheat and cotton co-growth stage and the key growth stages of cotton only. [Result] The AP contents were significantly influenced by the cropping systems on different dates. In the co-growth stage, the AP content in the cotton monoculture was higher than that in 3-1, at 20.98% on May 12 and 24.26% on June 7. After wheat was harvested (July 3 and August 4), there were no significant differences among the three cropping systems, and in the boll-opening stage of cotton, the order of the AP contents were as follows: cotton monoculture＞6-2＞3-1. In the vertical direction, the AP contents decreased as the soil depth increased, while in the horizontal direction, the AP distribution was influenced significantly by the cropping system. Based on the semivariance, there were strong spatial dependencies in the vertical direction in all three cropping systems. [Conclusion] Wheat-cotton double-cropping systems changed the distribution of soil AP, but had no influence on the spatial heterogeneity of the soil AP in the vertical direction. Geo-statistics provide a more intuitive method and guide to study the soil nutrients of the wheat–cotton and other double-cropping systems.