Unveiling spatial heterogeneity of soil available phosphorus for site-specific fertilization in Andisols of Hokkaido, Japan

Predicting the spatial variability of soil available phosphorus (P) is crucial for efficient site-specific fertilizer management in large-scale fields. In Hokkaido, Japan, Andisols are the dominant cultivated soil type, known for their high P fixation and strong spatial heterogeneity of inherent soil properties. To assess the magnitude and factors controlling the within-field variation in soil available P, a total of 920 surface soil samples were collected from two fields located 300 m apart, designated the East (6.6ha) and West (4.4ha) fields. The samples were analyzed for available P, phosphate absorption coefficient (PAC), total carbon (TC), and oxalate-extracted aluminum (Al _o ). The two fields had clear zones of low, medium, and high soil available P; however, the zoning was more pronounced in the East field. The available P was also higher in the East field, averaging 70.1 mg kg ^-1 , while it averaged 45.7 mg kg ^-1 in the West. The analysis of the spatial structure of the available P showed moderate spatial dependence (25 < nugget% ≤ 75) in both fields, but a larger range in the East field. PAC was a strong predictor of available P in the West field, whereas both TC and PAC controlled available P in the East field. Despite high Al _o concentration in the West field, the PAC was lower than in the East, indicating multiple factors controlling P variability. Overall, this study revealed that site-specific fertilization of P is needed, and management zones should be created based on the variation of soil organic matter and clay minerals.