Peer-Reviewed Journal Details
Mandatory Fields
Ciaran Lewis, Rashad Rafique, Nelius Foley, Paul Leahy, Gerard Morgan, John Albertson, Sandeep Kumar, Gerard Kiely
Journal of Environmental Sciences
Seasonal exports of phosphorus from intensively fertilised nested grassland catchment
In Press
Optional Fields
phosphorus; fertilizer; slurry; exports; grassland; land management; water quality; eutrophication

We carried out a one year (2002) study of phosphorus (P) loss from soil to water in three nested grassland catchments (17 ha, 211 ha and 1524 ha) with known P input in chemical fertilizer and animal liquid slurry applications. The specific objectives were: to determine the seasonal and annual exports in stream flow of total phosphorus (TP), total dissolved phosphorus (TDP) and particulate phosphorus (PP) and to examine the hydrological and chemical controls on P exports in the stream-flow. Chemical fertilizer was applied to the grasslands between March and September and animal slurry was applied over the twelve months. The annual chemical P fertilizer applications for the 17 and 211 ha catchments were 16.4 and 23.7 kg P/ha respectively and the annual slurry applications were 10.7 and 14.0 kg P/ha respectively. The annual TP export in stream-flow was 2.61, 2.48 and 1.61 kg P/ha for the 17, 211 and 1524 ha catchments, respectively compared with a maximum permissible (by regulation) annual export of ca. 0.35 kg P/ha. The export rate (ratio of TP export to P in land applications) was 9.6% and 6.6% from the 17 and 211 ha catchments, respectively. On average, 70% of stream flow and 85% of the P export occurred during the five wet Autumn/Winter months (October to February) indicating that when precipitation is much greater than evaporation, the hydrological conditions are most favourable for P export. However the soil quality and land use history may vary the results. Particulate P made up 22%, 43% and 37% of the TP export at the 17, 211 and 1524 ha catchment areas, respectively. As the chemical fertilizer was spread during the grass growth months (March to September), it has less immediate impact on stream water quality than the slurry applications. We also show that as the catchment scale increases, the P concentrations and P export decrease, confirming dilution due to increasing rural catchment size. In the longer term, the excess P from fertilizer maintains high soil P levels, an antecedent condition favourable to P loss from soil to water. This study confirms the significant negative water quality impact of excess P applications, particularly liquid animal slurry applications in wet winter months. The findings of this study suggest that the restricted P application in wet months can largely reduce the P losses from soil to water.

Grant Details