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Phosphorus Losses from Agricultural Watersheds in the Mississippi Delta
Citation:
YUAN, Y., M. A. Locke, R. L. Bingner, AND R. A. Rebich. Phosphorus Losses from Agricultural Watersheds in the Mississippi Delta. AGRICULTURE, ECOSYSTEMS & ENVIRONMENT. Elsevier Science Ltd, New York, NY, 115:14-20, (2012).
Impact/Purpose:
30 Phosphorus (P) is an essential nutrient for all life forms, but is often not applied as much as nitrogen in agricultural fields. Research has shown that a deficiency of P in soils limits crop production (Maples and Heogh, 1973; Havlin et al., 1999), whereas higher levels of P in soils often lead to P losses via surface runoff (Sharpley, 1995; Sharpley et al., 1996; Pote et al., 1996 and 1999; Daverede et al., 2003). An abundance of P in fresh water can lead to algal blooms, which have many detrimental effects on natural ecosystems (Sharpley et al., 1994). Odors and discoloration caused by decay of algal interfere with recreational and aesthetic water use, algae blooms shade submerged aquatic vegetation and reduce or eliminate photosynthesis and productivity, and algae may clog water treatment plant filters (Sharpley et al., 1994). Therefore, the U.S. Environmental Protection Agency (USEPA) has recommended that the total P (TP) level in natural rivers or streams should not exceed 0.01-0.1 mg/L depending on aggregate ecoregions in order to prevent nuisance growth of plants and eutrophication (USEPA, 2002).
Description:
High phosphorus (P) loss from agricultural fields has been an environmental concern because of potential water quality problems in streams and lakes. To better understand the process of P loss, rainfall, surface runoff, sediment, ortho-P and total P (TP) were measured (1996 to 2000) for three agricultural fields (UL1, UL2, and BL3) mainly in cotton production in Mississippi Delta watersheds; agricultural management practices during the study period also were recorded. Ortho-P concentrations ranged from 0.01 to 1.0 mg/L with a mean of 0.17 mg/L at UL1 (17.0 ha.), 0.36 mg/L at UL2 (11.2 ha.) and 0.12 mg/L at BL3 (7.2 ha.). The TP concentrations ranged from 0.14 to 7.9 mg/L with a mean of 0.96 mg/L at UL1, 1.1 mg/L at UL2 and 1.29 mg/L at BL3. Among the three sites, UL1 and UL2 received P application in the fall 1998, and BL3 received P applications in the spring of 1998 and 1999. High P concentrations were observed in surface runoff that was not always a direct result of P fertilizer application or high rainfall. However, P fertilizer application did influence P losses. Application of P in the fall (UL and UL2) resulted in more ortho-P losses, likely because high rainfall usually occurred in the winter months soon after application. The mean ortho-P concentrations were higher at UL1 and UL2 than that at BL3 although BL3 received more P application during the monitoring period. However, tillage associated with planting and incorporating applied P in the spring (BL3) may have resulted in more TP loss in sediment, thus the mean of TP concentration was the highest at BL3. Ortho-P loss was correlated with surface runoff; and TP loss was correlated with sediment loss. These results indicate that applying P fertilizer in the spring may be recommended to reduce potential ortho-P loss during the dormant season; in addition, conservation practices may reduce potential TP loss associated with soil loss.