Abstract
Sharpley, A.N., T. Daniel, T. Sims, J. Lemunyon, R. Stevens,
and R. Parry. 2003. Agricultural Phosphorus and Eutrophication,
2nd ed. U.S. epartment
of Agriculture, Agricultural Research Service, ARS.149, 44 pp.
Inputs of phosphorus (P) are essential for profitable crop and
livestock agriculture. However, P export in watershed runoff can
accelerate the eutrophication of receiving fresh waters. The rapid
growth and intensification of crop and livestock farming in many
areas has created regional imbalances in P inputs in feed and
fertilizer and P output in farm produce. In many of these areas,
soil P has built up to levels in excess of crop needs and now
has the potential to enrich surface runoff with P.
The overall goal of our efforts to reduce P losses from agriculture
to water should be to increase P use-efficiency, balance P inputs
in feed and fertilizer into a watershed with P output in crop
and animal produce, and manage the level of P in the soil. Reducing
P loss in agricultural runoff may be brought about by source and
transport control strategies. This includes refining feed rations,
using feed additives to increase P absorption by animals, moving
manure from surplus to deficit areas, finding alternative uses
for manure, and targeting conservation practices, such as reduced
tillage, buffer strips, and cover crops, to critical areas of
P export from a watershed. In these critical areas, high P soils
coincide with parts of the
landscape where surface runoff and erosion potential are high.
Keywords: eutrophication, fertilizer, phosphorus, P input,
P output, runoff
Contents
Introduction .........................................................................................
1
Eutrophication ..................................................................................
1
Agricultural Production ....................................................................
2
Soil Phosphorus ...................................................................................
5
The Loss of Phosphorus in Agricultural Runoff ...............................
10
Forms and Processes .......................................................................
10
The Dependence of Agricultural Runoff P on Soil P .....................
12
Remediation .......................................................................................
14
Source Management .......................................................................
15
Transport Management ...................................................................
21
Targeting Remediation ...................................................................
22
Making Management Decisions.......................................................28
Summary............................................................................................
31
References .........................................................................................
34