Potential for preferential pathways of phosphorus transport

This paper briefly reviews the existing literature and uses evidence from t hree studies to demonstrate the occurrence of preferential pathways of P tr ansport through soil. Studies conducted in the St. Lawrence lowlands, Canad a, indicated that particulate P (PP-i.e., >0.45 mu m) is the main fraction of total P (TP) in tile-drainage water generated by storm events after peri ods of low rainfall. In the remainder of the year, the concentration of TP and P forms were related to soil texture, primary tillage intensity and fre quency, and showed wide seasonal variations. For a study conducted in the U K under grassland, higher TP concentrations were found in near-surface runo ff (0-30 cm) compared with concentrations measured in drainflow. Water pass ing through the artificial drainage system had a higher proportion of PP (4 3%) than water passing close to (<30 cm) or over the soil surface (31%). In stallation of tile drainage in a poorly draining soil reduces P transfer by improving the infiltration capacity, thereby reducing overland flow volume and allowing P to be retained/sorbed by the soil matrix. Because of the ab sence of tillage, permanent grasslands accumulate P near the surface. We hy pothesize that, if the soil P store is coincident with preferential flow pa thways (either artificial mole drainage channels or natural macropores), pe rmanent grassland will be vulnerable to transfer large amounts of P through subsurface pathways. Phosphorus transfer through preferential flow pathway s may be particularly important after storm events that rapidly follow peri ods of drought and/or surface P inputs as inorganic fertilizer or manure.