Optimizing Phosphorus Use Efficiency with Nutrient Balances
One of the most commonly used agricultural phosphorus (P) performance indicators is the nutrient balance, writes Heidi Peterson, Director, Phosphorus Program, International Plant Nutrition Institute. They can be applied at a variety of spatial and temporal scales to evaluate the efficiency of a system by quantifying the amount of a nutrient removed from a system relative to the amount applied. When analyzed together with data on soil fertility and crop productivity, results can be a long-term indicator of whether a system is being managed sustainably while minimizing excess nutrient losses.
Farm-scale P nutrient balances can be approached from two different perspectives: cropland P use or the whole farm system. To understand cropland P use efficiency (PUE), P inputs include fertilizer or manure applied to the crops, including all inorganic and organic sources. To adequately account for P inputs from manure or non-conventional sources, a chemical analysis should be completed. The P outputs harvested include the nutrients taken up by the crop and removed from the field.
Phosphorus Use Efficiency (PUE) = (P outputs) / (P inputs)
Cropland PUE <1 indicates that the P input is greater than the harvested crop needs, contributing to increased soil test P (STP) and potential for losses to the environment. Cropland PUE =1 indicates that inputs are equal to the harvested crop output. This could be considered sustainable for some time if the STP is above the optimum concentration; however, this is not the case if STP is below the critical concentration or in a region with low natural soil fertility. Cropland PUE >1 indicates that more nutrients are removed from the harvested crop than applied, suggesting that the harvested crop is mining soil P.