Phosphorus Leaching in a Soil Textural Gradient: Injection VS Surface Application of Cattle Slurry.

Texture is a major factor influencing mobilization and transport of P in soil owing partly to differences in adsorptive properties, and partly to differences in pore-size distribution and pore organization. Slurry application strategies may be important mitigation measures for reducing agricultural P leaching. We propose diverse interactions between dominant flow pathways and cattle slurry:

- Injection of slurry reduces P leaching compared to surface application in soils with preferential flow behaviour

- Injection of slurry has less impact on P leaching compared to surface application in soils with matrix dominated flow behaviour

We tested these hypotheses on three textural soil classes (Olsen-P 1.6 mg P 100 g^-1) on intact soil columns (20*20 cm) and compared them to in situ P leaching before slurry application. In a loamy sand P leaching with both slurry application techniques slightly exceeded the in situ leaching. However, the two application techniques did not vary significantly. In a sandy and a clay loam preferential flow paths within the soil columns caused high P leaching when slurry was applied at the soil surface. The effect increased with increasing clay content. Injection of slurry did not exceed the in situ P leaching in these soils. After slurry application (with both techniques) dissolved P became increasingly present in the leachates of all soils. Additionally, the dominant form of dissolved P changed from inorganic to organic P after slurry application (with both techniques) in all soils, and especially with surface application in the clay loam. These results document the importance of soil texture while dealing with agricultural management to reduce P leaching. In soils with preferential flow behaviour injection of slurry significantly reduced P losses from the plough layer compared to surface application. This was observed to a much lesser extent in a soil with matrix dominated flow.