Overview & Objectives


The importance of agricultural P management in protecting water quality was addressed in Lesson I of this series [Manure Phosphorus (P) and Surface Water Protection 1:  Basic Concepts of Soil and Water P].  Factors contributing to P loss from land to surface waters include source factors and transport factors (Table 1).  As discussed in Lesson I, an interaction of source and transport factors is needed to have runoff P loss.  If either source or transport factors contributes minimally to the risk of P delivery to surface waters, then the risk for P delivery is not likely to be great, even if the other set of factors creates a much greater risk potential.  The 'critical source area' concept, introduced in Lesson II, tells us the risk is greatest when both the source and transport factors are high.

The current lesson addresses transport factors that may contribute to P delivery to surface waters, the most important being erosion, runoff, subsurface flow, drainage and distance to surface water (Fig. 1).  In some instances, wind erosion may also play an important role.  The lesson also discusses the effects of management practices on P transport and water-related transport processes.


Upon completing this lesson, a student should be able to:

1. Identify transport factors and analyze their importance for P delivery to surface waters.

2. Describe the interaction of erosion with soil test P and total soil P relative to P in runoff and erosion.

3. Name and discuss the role of management practices in reducing the effect of transport factors contributing to P loss from a field.


Site and management factors 


Transport factors

Soil P levels


P application practices, including time, rate and method of application

Erosion from rainfall, snowmelt and irrigation events

Field management practices, such as tillage practices and use of cover crops

Surface and subsurface drainage


Percolation and underground movement of P to seepage areas


Distance from P source to concentrated water flow or a water body


Stream bank/bed cutting


Atmospheric deposition

Copyright 2005

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 1047. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s).