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Manure Phosphorus and Surface Water Protection II: Field and Management Factors: Objectives Manure Phosphorus (P) and Surface Water Protection II: Field and Management Factor Charles Wortmann Department of Agronomy and Horticulture at University of Nebraska-Lincoln, USA Deana Namuth Department of Agronomy and Horticulture at University of Nebraska-Lincoln, USA (http://agronomy.unl.edu) 2005 Lesson Navigation Tips: - Click on 'Animations' button found to the left in order to view the animation which supplements this lesson. You can also click on the animation icon within the text. - Click once on figures to see enlarged versions. - Click once on words in color to bring up their definitions. Overview: The importance of managing agricultural phosphorus (P) to protect of water quality was addressed in module I. Factors contributing to P loss from the land to surface waters include site and management factors (source factors) and transport factors (Table 1). An interaction of source and transport factors is needed to have runoff P loss. If one set contributes minimally to risk, then risk is not likely to be great even if the other set of factors offers much potential for risk. This raises the concept of "critical source area" (Fig. 1); the risk is greatest when both the source and transport factors are high. Figure 1. The critical source area concept for loss of agricultural P to surface waters. This lesson describes how the source factors, including soil characteristics and management practices, affect P delivery to surface waters. Crop producers have some control over these factors and management practices are discussed. Table 1 Site and management factors Transport factors Soil P levels Runoff P application practices including time, rate and method of application Erosion from rainfall and snowmelt events and from irrigation events Field management practices such as tillage practices and use of cover crops Surface and sub-surface drainage Percolation and under-ground movement of P to seepage areas Distance from P source to concentrated water flow or a water body Atmospheric deposition Objectives: Upon completing this lesson, a student should be able to: 1. Identify source factors, and analyze their importance, for P delivery to surface waters. 2. Describe the relationship of soil test P and total soil P with P in runoff. 3. Identify P application factors, and analyze their importance, for P delivery to surface waters. 4. Discuss the reactions of manure P with soil following manure application. 5. Discuss deep plowing as a means to reducing P delivery from crop land. 6. Name and discuss the role of three management practices to reduce the potential of source factors in contributing to P loss from a field. Discussion Question : What are the major source factors in your State? Development of this lesson was supported in part by a University of Nebraska Cooperative Extension grant. A contribution of the University of Nebraska Cooperative Extension, Journal Series _____. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s).