What is Phosphorus?

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Phosphorus is a nutrient required in plants for several complex functions such as energy transformation, photosynthesis, nutrient movement, sugar and starch transformation, and genetic transfer. The general forms of phosphorus in the soil include plant available inorganic phosphorus as well as plant unavailable forms such as organic phosphorus, adsorbed phosphorus, and primary mineral phosphorus.

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Regional Educator ResourcesOther Educator ResourcesTechnical Resources
Title Source Resource type and Date Short Summary / Preview
Understanding phosphorus fertilizers University of Minnesota Extension Webpage


When producers pay special attention to managing phosphorus (P), it can lead to profitable crop production. The best way to use fertilizers to meet P requirements changes with crop, soil properties and environmental conditions.
Soil Phosphorus USDA NRCS Educator Guide

May 2014

This is a very comprehensive guide on soil phosphorus for educators. This publication lists the functions of phosphorus in growing crops and forages, shows the phosphorus cycle, explains inherent factors affecting soil phosphorus, and describes phosphorus management for crops. The guide also explains a method for measuring phosphate (PO4), how this relates to soil health and provides an example of phosphorus soil test results and fertilizer recommendations for corn.
Strategies to Minimize Phosphorus Loss From Your Farm University of Missouri Extension Publication

Nov 2018

This guide discusses steps you can take to reduce phosphorus loss from your farm.
Managing Manure Phosphorus to Protect Water Quality University of Missouri Extension Publication

Nov 2018

This guide defines the unique aspects of managing manure as a phosphorus fertilizer source and provides practical information about management strategies to reduce phosphorus losses from your farm.
Understanding phosphorus in Minnesota soils University of Minnesota Extension Webpage


In Minnesota, most agricultural soils contain between 100 and about 4,000 pounds of total P per acre. Efficiently using this phosphorus is becoming more important due to economic and environmental concerns.
Agronomic and environmental management of phosphorus University of Minnesota Extension Webpage


Use conservation tillage systems to reduce the amount of soil lost by erosion. Band or inject phosphate fertilizers and manure below the soil surface.
Phosphorus: Transport to and availability in surface waters University of Minnesota Extension Webpage


A number of phosphorus (P) sources contaminate surface waters. These include agriculture, municipal sewage treatment plants, individual septic treatment systems, decaying plant material, runoff from urban areas and construction sites, stream bank erosion and wildlife.
The Minnesota Phosphorus Index: Assessing risk of phosphorus loss from cropland University of Minnesota Extension Webpage


Fact sheet where they explain when and how to assess the risk of phosphorus loss from cropland using the Minnesota Phosphorus Index.
Soil Quality Indicators: Chemical Indicators and Soil Functions USDA-NRCS Fact sheet

Feb 2015

Fact Sheet. Different chemical indicators widely used are related to the respective basic functions they measure.
Understanding Soil Tests for Plant-Available Phosphorus Ohio State University Extension Publication

Jun 2007

Much effort has been dedicated to the development of soil tests that determine the concentration of plant-available P,  and whether or not that concentration is sufficient for optimum crop growth.
Selection of an Appropriate Phosphorus Test for Soils USDA-NRCS Fact sheet

Not Dated

When extracting solution is added to soil, there are four basic reactions by which P is removed from the solid phase: 1) dissolving action of acids, 2) anion replacement to enhance desorption, 3) complexing of cations binding P, and 4) hydrolysis of cations binding P. Therefore, the selection of a P soil test depends on the chemical forms of P in the soil.
Manure Land Application and Soil Health Indicators Soil Health Nexus Working group report

Sep 2017

Manure increases soil phosphorus. Average phosphorus of soil samples with manure application was 92.9 ppm, which was almost twice the average value of the soil without manure application (49.0 ppm)
Phosphorus Math for Dummies Purdue University Extension Publication

May 2019

Publication examines ways to calculate the value of P2O5 in different phosphorus (P) fertilizers.
Phosphorus and Potassium Fertilization of Alfalfa Purdue University Extension Publication

Mar 2009

Publication explores phosphorus fertilization for alfalfa.
Wheat Production and Fertilization in Indiana Purdue University Extension Publication

Nov 1992

Publication reviews fertilizer recommendations (including phosphorus) for Indiana wheat production.
Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa Michigan State University, The Ohio State University, Purdue University Extension Publication

Jul 1995

In this publication, we have developed common fertilizer recommendations for the major crops in Michigan, Ohio and Indiana.
Agricultural Sources of Contaminants in Groundwater and Surface Water University of Missouri Extension Publication

Jun 2017

In agriculture, pesticides and plant nutrients can enter groundwater and surface water and contaminate it. These products may reach large enough levels to become harmful to animals and people, so we must understand how contamination may occur and how it can be avoided. With good management practices, we can keep groundwater and surface water from becoming contaminated by pesticides and nutrients.
Management of Nitrogen and Phosphorus SARE Book Excerpt


Both nitrogen and phosphorus are needed by plants in large amounts, and both can cause environmental harm when present in excess.
Building Soil Fertility & Tilth With Cover Crops SARE Book Chapter


Cover crops contribute indirectly to overall soil health by catching nutrients before they can leach out of the soil profile or, in the case of legumes, by adding nitrogen to the soil. Their roots can even help unlock some nutrients, converting them to more available forms.
Title Source Resource type and date Short Summary
Managing Phosphorus for Crop Production Penn State Extension Publication


In general, crop use of any nutrient depends on a two-step process: soil supply of that nutrient in an available form, and uptake of that available nutrient by the crop.
Soil Nutrient Management For Forages: Phosphorus, Potassium, Sulphur, and Micronutrients Montana State University Extension Publication


Improvements in forage production have the potential to increase income and significantly reduce livestock production costs. Soil fertility is important for forage production, stand health/longevity, and forage quality.
Title Source Resource type and Date Short Summary
Differentiating and Understanding the Mehlich 3, Bray, and Olsen Soil Phosphorus Tests Iowa State University Presentation

Not Dated

PowerPoint presentation on methods.
Soil Sampling for P, K, and Lime Recommendations Purdue University Extension Publication

Feb 1995

Publication examines field crop soil sampling considerations (including phosphorus).
Extractable Phosphorus University of Minnesota University Webpage

Not Dated

The soil phosphorus measured is that which is extracted by a solution consisting of 0.025 normal HCl and 0.03 normal NH4F, referred to as Bray-1 extractant.
MCSE: Inorganic and Organic Soil Phosphorous Fractions Michigan State University, LTER Extension/Research Protocol

Not Dated

Protocol to measure soil phosphorus using the Phosphorus Sequential Fractionation Method.
Laboratory Analysis of Manure University of Missouri Extension Webpage

Nov 2018

To make efficient use of fertilizer nutrients in manure, nutrient levels must be determined by laboratory analysis. This publication outlines methods for obtaining and interpreting laboratory analyses of manure.
Phosphorus and Soil Health Management Practices Agricultural & Environmental Letters Peer-Reviewed Publication

Jul 2019

A literature review points to well-established findings regarding trade-offs in water quality outcomes following the implementation of core soil health practices. In fact, both conservation tillage and cover crops can exacerbate dissolved P losses, undermining other benefits such as reductions in particulate P (sediment-bound P) losses.
Extractable Phosphorus – Bray Method University of California, Davis University Webpage

Not Dated

This method estimates the relative bioavailability of inorganic ortho-phosphate (PO4-P) in soils with acid to neutral pH.

Technical review: April 13, 2020