PHOSPHORUS LOSSES IN SUBSURFACE DRAINAGE BEFORE AND AFTER MANURE APPLICATION TO INTENSIVELY FARMED LAND

Authors: MCDOWELL, RICHARD - PENN STATE UNIVERSITY; Sharpley, Andrew

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2001
Publication Date: 1/30/2001
Citation: McDowell, R.W., Sharpley, A.N. 2001. Phosphorus losses in subsurface flow before and after manure application to intensively farmed land. Science Of The Total Environment. 278:113-125.

Interpretive Summary: In sustainable agroecosystems, fertilizers and manures should be managed to maintain a productive soil, while minimizing the potential for phosphorus loss in overland and subsurface flow and potential eutrophication of surface waters. The application of phosphorus in excess of plant requirements leads to a buildup of soil phosphorus and increased loss of phosphorus in agricultural runoff. Many advocates of decreasing phosphoru loss from soil to water have focused attention on management practices that minimize the potential for phosphorus transfer by overland flow. One such strategy is to retire land that had previously been intensively managed or to impose conservation measures that reduce erosion, such as converting cultivated fields to grass. The latter is commonplace in the establishment of buffer strips. However, while such strategies may successfully decrease the contribution of phosphorus to surface waters via overland flow, phosphorus in subsurface pathways may contribute concentrations of phosphorus that remain above those required to stimulate eutrophication. The results of this study show that following the addition of manure at rates recommended in Pennsylvania, USA, phosphorus concentrations in drainage water can exceed current estimates of those required to promote eutrophication of surface waters. Our findings suggest that despite the establishment of a fast growing grass sward to simulate a buffer strip, phosphorus concentrations in the short-term (less than one year) would not be mitigated, due to the large contribution of phosphorus in subsurface pathways.

Technical Abstract: A study was conducted to examine the loss of P in dissolved and unreactive P forms in subsurface flow from three cultivated soils of varying soil P concentrations. Measurements were made in drainage waters from the cultivated soils before and then three weeks after sowing the soils to pasture (to simulate the establishment of a buffer strip) and applying manure at rates recommended for Pennsylvania (which depended upon the concentration of P in the topsoil). An additional measurement of P forms in drainage waters was made one year later. Results showed that Dissolved reactive P (DRP) concentrations in drainage water can exceed current estimates of those required to promote surface water eutrophication (0.05 mg/L) before (0.15 to 0.20 mg/L) and after (0.39 to 0.51 mg/L) the application of manure. Concentrations of DRP one year after manurial application increased compared to three weeks after application and was attributed to the slow movement of P (largely as reactive P) down the cultivated soil via matrix flow. Concentrations of soil P were significantly increased down the soil profile and attributed to the P saturation of soils before manurial application. The results suggest that despite the establishment of a fast growing grass sward to simulate a buffer strip, P concentrations would not be mitigated in the short-term (less than one year), due to the large contribution of P in subsurface pathways.