Indicators of phosphorus status in soils: significance and relevance for crop soils in Wallonia - A review

Introduction . P is an essential element for plant growth. So, it is essential to evaluate accurately its availability in the soil. It requires relevant indicators of P status. Literature . This paper reviews literature about the indicators of phosphorus (P) status in the soils. Many indicators can be found and amongst others, we can cite single extractions (soluble, available or total P) which are the most common indicators used worldwide. Over time, more complex P indicators have been developed as sequential extractions which characterize the different forms of P, degree of P saturation, diffusive gradients in thin films, biological extractions, isotopic methods or more complex models. To make a choice into them, different criteria should be applied as relevance, cost and time, ease of interpretation, and, the most important, objective of the analysis. Firstly, we describe the different types of indicators found in the literature and propose a classification. Secondly, we evaluate all the indicators cited above according to the SAFE criteria. Finally, we discuss the situation met in Wallonia. Conclusions . Each P indicator presents advantages, but also disadvantages. This review highlights the importance of well reflecting on the choice of an indicator and having interpretation thresholds.