De enkelvoudige versus de gecombineerde indicator voor bepaling van de fosfaattoestand van de bodem: toetsing op data van veeljarige veldproeven op grasland en bouwland

In the Netherlands, the application of phosphorus (P) from fertilising products is regulated through application rate limits targeting equilibrium fertilisation and a neutral P status of the soil meaning that a higher P application rate limit is assigned to soils with a low P status and vice versa. Until 2021, the soil P status was derived based on one single soil P indicator namely P-AL-value for grassland and Pw-value for arable land. From 2021 onwards, the soil P status will be derived from the combination of P-AL-value(indicator for the P capacity) and P-CaCl2 –value (indicator for P intensity) enabling to differentiate based on the P buffering capacity of the soil. Data from long term field trials supply valuable data on trends in soil P indicators in relation to crop uptake and P application rate. This report assesses trends in the single P indicator (Pw-value or P-AL-value) and combined indicator (P-AL-value and P-CaCl2-value) in relation to P fertilisation rate and P uptake rate using data from long term field experiments on grassland and arable land.