Manipulation of fertiliser regimes in phosphorus enriched soils can reduce phosphorus loss to leachate through an increase in pasture and microbial biomass production

Abstract

Phytoextraction of phosphorus (P) has been proposed as a strategy to reduce the potential for P loss from P enriched soils. Compared to pastures that receive adequate P fertilisers to maintain soil P concentrations, applying half maintenance rates, or no P, slowly decreases soil P concentration and P losses to water. We hypothesise that the quantity of P lost in leachate can be further decreased by the addition of nitrogen (N) fertiliser to stimulate plant-P uptake. A 451 day lysimeter trial investigated subsurface P losses from three New Zealand soil types (USDA soil taxonomy: Udand, Dystrudept and Vitrand) under three N fertiliser rates, zero, 150 and 300kgNha−1yr−1 and two rates of P fertiliser, zero and half maintenance application with regular cutting and removal of pasture. For two of the soil types (Dystrudept and Vitrand), N application increased pasture production and decreased the load of dissolved reactive P (DRP) leached by 53–76% and the load of total dissolved P (TDP) by 39–53% compared to when no N was applied. Furthermore, for these soils, compared to the no P and no N treatment, applying P at half the rate designed to maintain soil P concentration, decreased the load of DRP and TDP in leachate by a 62–68% and 54–59% due to immobilisation of P within the microbial biomass. A high sorption capacity, leading to slow but sustained release of P to the soil solution, was seen as the probable reason for the lack of treatment effect in the third soil (Udand). This study highlights the potential for manipulating fertiliser regimes and implementing a cut and carry system on critical source areas of P loss within a farm as a strategy to reduce P loss from P enriched pastoral soils without impacting on productivity.