Correlation of DGT-P and conventional soil P tests with rye shoot biomass and P uptake across temperate soils with differential soil properties

Several phosphorus (P) extraction tests are being used as soil P tests, but many studies have shown that the correlation of extractable P with plant yield and P uptake varies and sometimes is poor. Infinite sink extraction methods may be superior in estimating plant P availability. Soil P tests were evaluated for their power in determining plant-available P pools. Thirty arable soils covering different soil groups were tested for soil characteristics and extractable P pools. Rye was grown on these soils for six weeks and analysed for shoot yield and shoot P concentrations. Correlations between soil P concentrations, shoot yield and shoot P content were investigated. Extractable P pools mostly significantly correlated with soil pH, texture and amorphous iron oxide content. High and significant correlations were found among most of the extractable soil P pools, except for calcium acetate lactate (CAL)-extractable P. In contrast to previous studies, diffusive gradients in thin films (DGT)-extractable P employed in our pot experiment did not perform better than other extraction methods in correlating with plant available P and uptake, likely because water availability was not a limiting factor of P diffusion. Plant-available P in the soils investigated in this study was controlled by P quantity (i.e. the amount of adsorbed P) and P intensity (i.e. the soil solution P). We conclude that the advantage of infinite sink extraction methods over equilibrium-based techniques becomes less apparent if P is not strongly intensity-controlled and water availability is not a limiting factor of P diffusion.