Challenges in Assessment of Legacy Phosphorus.

Legacy phosphorus in soils makes it difficult to evaluate effects of current practices from historical land management. Information on legacy P stored within a soil system is needed both for environmental risk assessment as well as for agronomic P application recommendations.  A one-size-fits-all approach to implementation of best management practices for identical land management poses additional difficulties when soil properties and source of P application are different at the various sites. The soil P storage capacity (SPSC) is a feasible site-specific means of evaluating the P storage limits prior to runoff and/or leaching risks without the need for any prior P-application records.  The SPSC, calculated from P, Fe and Al in a soil test solution such as Mehlich 3, can be used for (though not limited to): i) explaining differing P loss from identically managed agricultural sites, ii) assisting in water table management at differing P-impacted sites, iii) evaluating the consequences of leaving manure-P in soil over a period of time, and iv) predicting edge-of-field water quality.