es, plant residues, and/or any recently applied commercial fertilizers into lakes, ponds, streams, rivers and bays. The risk for soluble P losses is increased when the concentration of P in the soil exceeds the natural soil P holding capacity. The sandy soils of Delaware have naturally have low P-holding capacity. In some cases, P can be carried downward, or leached, through the soil and may eventually reach groundwater.
Once transported into water bodies or groundwater, inorganic P can become a water pollutant. For example, P lost in runoff or leachate may contribute to eutrophication of Delaware’s surface water bodies. Eutrophication is the enrichment of water with nutrients that results in excessive aquatic plant (mostly algae) growth. With time, oxygen depletion of eutrophic waters can lead to fish kills and the accompanying foul smell. Eutrophic water bodies can often no longer be used for fishing, swimming, boating, or other recreational activities.
Can I Test My Soil for Phosphorus?
Phosphorus is one of the elements for which soil testing is useful. When testing is performed by a reputable agricultural laboratory, the results indicate the relative availability of soil P. Soil test results help producers and consultants properly manage application of manure. The soil test report from the University of Delaware Soil Testing Program, or other reputable regional laboratory, will include recommendations for P fertilizer rates for crops if results indicate that P fertilization is necessary.
Contact your county Extension office for more information about soil testing and taking a soil sample.
How Can You Help Protect Water Quality
As a grower in Delaware, you can help protect water quality by following best management practices (BMPs) when using fertilizers and manure. Fertilizer and manure applications are restricted to a three year crop-removal rate on “high P” soils (>150 FIV) to protect water quality. Alternatively, growers may opt to conduct a P Site Index to determine if other P management strategies (i.e., N-based management during one or more years of a crop rotation) are permitted.
Boyd, C.E. 1982. Liming fish ponds. Journal of Soil and Water Conservation 37:86-88.
Shober, A.L. 2008. Soils and fertilizers for Master Gardeners: Phosphorus in the home landscape. EDIS Document SL261/MG446. University of Florida – IFAS, Gainesville, FL. http://edis.ifas.ufl.edu/MG446
Richard Taylor, Agronomy Extension Specialist (retired), University of Delaware
Original Publication Date: September 2015. Adapted from an original document prepared by A.L. Shober for UF-IFAS.
Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin.
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