Phosphorus Management at the Watershed Scale: A Modification of the Phosphorus Index

Abstract

We considered hydrologic and chemical factors controlling P export from a 39.5-ha mixed land use watershed in east-central Pennsylvania, focusing our evaluation on watershed vulnerability to P loss. The spatial variations of P source factors, soil P, and P inputs from fertilizer and manure were evaluated. Distribution of Mehlich-3 soil P on a 30-m grid over the watershed showed that soil P varied with land use. Soils in wooded areas had low Mehlich-3 P (<30 mg kg" 1); grazed pasture had Mehlich-3 P values between 100 and 200 mg kg '; and cropped fields receiving manure and fertilizer applications were mostly >200 mg kg" 1. Phosphorus sources and transport controls on P loss were evaluated by examining in-stream P concentrations during storm hydrographs. Phosphorus concentrations decreased 50% downstream from headwaters to watershed outlet, and were more closely related to near-stream (within 60 m) distribution of high-P soils than to that of the whole watershed. This suggests that near-stream surface runoff and soil P are controlling P export from the watershed. Based on these findings, we modified the Phosphorus Index (P1), a useroriented tool developed by the NRCS-USDA to identify critical source areas controlling P export from agricultural watersheds. The modification separately evaluates P source and transport factors, and incorporates the hydrologic return period to describe contributing areas. The modified P1 was applied to the watershed to illustrate interactions between P source and transport processes controlling P export, and approaches for managing P loss.

Grazing Management Effects on Sediment and Phosphorus in Surface Runoff

“…Damage caused by treading (Elliott et al 2002), decreased soil organic matter (Naeth et al 1991b;Betteridge et al 1999), and reduced leaf litter results in a reduction of aboveground water-holding capacity of the soil (Naeth et al 1991a), decreasing infiltration rate and increasing the volume of surface runoff. Management practices that reduce the total volume of surface runoff and encourage infiltration will reduce the potential for sediment and P losses from pastures (Gburek et al 2000).…”

The Potential of P Loss from Livestock Farms to Watercourses in Wensleydale; A Risk Mapping Approach

“…Source factors are important in order to estimate nutrient availability such as P availability, yet delivery of P is conditioned by transport factors [27]. In fact, "transport factors are what transform potential P sources into actual P losses from a field or watershed" [33]. Hence, a risk assessment method is selected in this study in order to determine the potential for P loss from livestock farms in a non NVZ.…”

“…In this regard, steep slope and short distance of these intermediate sources to watercourses significantly increase the risk of nutrients loss [33]. Furthermore, it should be pointed out that Farm 4 received in 2009 a report from the ECSFDI where several recommendations were made in order to prevent polluted water from entering the nearby stream.…”

Evaluation of phosphorus and nitrogen balances as an indicator for the impact of agriculture on environment: A comparison of a case study from Poland and Mississippi US

“…The use of P from mineral fertilizers was always important for plant production, but in the last decade it became a source of potential risk to environmental contamination [50,51]. Although excessive phosphorus accumulation in the soil may have a negative influence on environment, leading to eutrophication [52][53][54][55][56], it should be noted that the relation between the phosphorus content in the soils and its leaching dynamics are still not yet understood. Sharpley [57] showed that the amount of P leached to surface waters is the function of plant growth system and of soil quality.…”