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United States Department of Agriculture

Agricultural Research Service

Research Project: UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS Title: Phosphorus losses from agricultural watersheds in the Mississippi Delta

Authors
item Yuan, Yongping -
item Locke, Martin
item Bingner, Ronald
item Rebich, Richard -

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 2012
Publication Date: January 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/56936
Citation: Yuan, Y., Locke, M.A., Bingner, R.L., Rebich, R. 2013. Phosphorus losses from agricultural watersheds in the Mississippi Delta. Journal of Environmental Management. 115:14-20.

Interpretive Summary: Agricultural management practices have been studied for reducing nonpoint source pollution and improving water quality. The Mississippi Delta (flood plain of Mississippi River) is an important agricultural region of the United States, and high phosphorus (P) loss from the region has been an environmental concern because of potential water quality problems in streams and lakes. Therefore, the overall objectives of this study were to identify factors that affect P losses from agricultural fields in two Mississippi Delta watersheds to improve the understanding of P losses and assess whether management practices might mitigate these losses. The paper presents results of rainfall, runoff, orthophosphorus (ortho-P), total phosphorus (TP) and sediment collected from three agricultural fields mainly in cotton production in Mississippi Delta watersheds. Agricultural management practices during the study period also were recorded. It was found that application of P in the fall resulted in more ortho-P losses, likely because high rainfall usually occurred in the winter months soon after P application. However, tillage associated with planting and incorporating applied P in spring may have resulted in more TP loss in sediment. 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.

Technical Abstract: 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 application in the spring 1998 and 1999. It was found that the high P concentrations observed in surface runoff were 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 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.

Last Modified: 11/26/2014
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