| Abstrakt: |
Since its discovery in 1669, phosphorus (P) in the form of fertilizer has become an essential input for many agroecosystems. By introducing a concentrated P source, fertilizers increase short‐term P export potential soon after their application and longer‐term export potential by increasing soil fertility (legacy P). The 4R concept was developed to help mitigate P exports from the fertilizers that sustain agricultural productivity. This review investigates the factors affecting P exports soon after the application of mineral fertilizers to pasture‐based grazing systems and studies quantifying its potential impact in different systems, with an emphasis on Australasia. Initially, P fertilizers and reactions that might affect their short‐term P export potential are reviewed, along with P transport pathways, the forms of P exported from grazing systems, factors affecting P mobilization into water, and studies demonstrating the possible short‐term effects of fertilizer application on P exports. Using that foundation, we review studies quantifying the short‐term impact of fertilizer application in different regions; they show that under poor management, recently applied fertilizer can contribute a considerable proportion (30–80%) of total farm P exports in drainage, but when fertilizer is well‐managed, that figure is expected to be <10%. We then use three model systems of varying hydrology that are common to Australasia to demonstrate the principles for selecting fertilizers that are likely to minimize P exports soon after their application. Fertilizers increase P exports directly or by increasing P cycling.We review P pathways and processes relevant to grazing systems.Direct fertilizer P exports can be comparatively small (<10% of annual exports).Fertilizer selection to minimize P exports in three model systems is demonstrated. |
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