Diffusive Gradients in Thin Films as a Reference Method for Assessing Soil Phosphorus by Visual and Near‐Infrared Spectroscopy

Phosphorus (P) deficiency is a severe challenge in many agricultural areas around the globe, while at the same time, aquatic environments are threatened by leaching and runoff of excess P in other areas. Accurate, cheap, and rapid assessment of crop P needs and risk of P loss is therefore necessary to optimize the use of P fertilizer worldwide. The purpose of this study was to develop a method to predict soil P concentrations by visual and near‐infrared spectroscopy using reference P concentrations determined by diffusive gradients in thin films (DGT); Olsen P results were included for comparison. The study was conducted on paddy soils from six main rice‐producing ( Oryza sativa L.) provinces in southern China. Using DGT P as a reference resulted in a better visual and near‐infrared calibration to predict soil P concentrations, as compared with using Olsen P. Core Ideas Determining soil P by Vis‐NIR spectroscopy is possible. Using DGT P as the reference method is superior to using Olsen P. Less variation in soil properties is likely to increase model quality. Soil organic matter, improving plant P availability, affects DGT P more than Olsen P.