Phosphorus source and the transport of phosphorus in surface runoff

Authors: SHIGAKI, FRANCIROSE - UNIV OF SAO PAULO; Sharpley, Andrew; PROCHNOW, LUIS - UNIV OF SAO PAULO

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2006
Publication Date: 10/27/2006
Citation: Shigaki, F., Sharpley, A.N., Prochnow, L. 2006. Phosphorus source and the transport of phosphorus in surface runoff. Journal of Environmental Quality. 35(6):2229-2235.

Interpretive Summary: Freshwater eutrophication is a major water quality concern in the United States, and can be greatly accelerated by the influx of P in surface runoff from agricultural land. As P most often limits freshwater eutrophication, decreasing P loss in runoff has become a major target in minimizing surface water degradation. To meet crop production goals, however, P is routinely added to soil. There are many types of P fertilizers available, such as organic (bone meal, cottonseed meal, fish emulsions, manures and processed sewage sludge) and inorganic (reactive rock phosphates, acidulated phosphates and thermophosphates) materials. Acidulated triplesuperphosphate (TSP) is the most commonly used fertilizer due to its high P solubility and immediate availability of P for crop uptake. Other fertilizers with lower water P solubility, such as highly reactive North Carolina rock phosphate (NCRP), swine manure (SM), and low grade single superphosphate (LGSSP), can be used to maintain a long-term source of P due to their residual availability. We added different sources of P varying in water soluble P content to grassed field plots and measured P loss in runoff. Results from our research showed the strong influence of water solubility of P sources in determining P concentration and loss in runoff. An increase in P loss was observed with an increase in source P solubility (TSP is greater than LGSSP is greater than SM is greater than NCRP is greater than control). A decision can be made regarding P source use based on expected environmental or agronomic response. While other studies have reported on the relative agronomic effectiveness of different types of P fertilizers, our research suggested that more agronomically effective P sources present a greater risk of runoff P enrichment. Conversely, LGSSP and NCRP may support lower concentrations of P in runoff than TSP. Nevertheless, if the crop is the main management consideration, then agronomic efficiencies should determine the source or type of P applied.

Technical Abstract: Continual application of mineral fertilizer and manures to meet crop production goals has resulted in the buildup of soil P concentrations in many areas. A rainfall simulation study was conducted to evaluate the effect of the application of P sources differing in water soluble P (WSP) concentration on P transport in runoff from 2 m**2 plots on three grassed and no-till soils (Alvira, Berks and Watson). Triple superphosphate (TSP) – 79% WSP, low-grade super single phosphate (LGSSP) – 50% WSP, North Caroline rock phosphate (NCRP) – 0.5% WSP, and swine manure (SM) – 30% WSP, were broadcast (100 kg total P ha**-1) and simulated rainfall (50 mm hr**-1 for 30 min) applied 1, 7, 21, and 42 d after P source application. In the first rainfall event one d after fertilizer application, dissolved reactive P (DRP) and total P (TP) concentrations of runoff increased for all soils with an increase of source WSP; with DRP averaging 0.27, 0.50, 14.66, 41.69 and 90.47 mg L**-1; and total P averaging 0.34, 0.61, 19.05, 43.1, and 98.06 mg L**-1 for the control, NCRP, SM, LGSSP and TSP, respectively. Sources did not influence runoff volume and soil type had no effect on P loss. The loss of P in runoff decreased with time for TSP and SM, such that after 42 d, losses from TSP, SM, and LGSSP did not differ. These results support P water solubility in P sources for consideration as an indicator of P loss potential.