What is Nitrogen?

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Nitrogen is an essential plant nutrient needed for growth, development, and reproduction that is a critical component of organic molecules such as proteins, amino acids, and nucleic acids. In addition, it plays a major role in many key plant metabolic processes, such as photosynthesis.

In soil, nitrogen may be found in two forms – mineralizable and plant available. Mineralizable nitrogen is found in organic soil components, and for plant use must be mineralized, or broken down, to simpler forms. Plant available (mineralized) nitrogen is in a form which can be readily utilized by plants and is commonly found in nitrogen forms such as nitrate (NO3), and ammonium, (NH4).

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Regional Educator ResourcesOther Educator ResourcesTechnical Resources
Title Source Resource type and Date Short Summary / Preview
Understanding nitrogen in soils University of Minnesota University Webpage


Numerous nitrogen (N) sources exist. Consider these when evaluating the N budget. Soil type and climate greatly affect nitrogen loss from the soil system.
Soil Nitrogen USDA-NRCS Educator Guide

not dated

Inherent factors such as soil drainage, soil texture, and slope steepness impact N-transport and N- transformation processes that limit availability to crops or lead to losses.
Integrated Pest Management Best Management Practices for Nitrogen Fertilizer in Missouri Plant Protection Programs College of Agriculture, Food and Natural Resources University of Missouri Extension Publication


This publication, focused on nitrogen, is part of a series of IPM Manuals prepared by the Plant Protection Programs of the University of Missouri. Successful nitrogen management delivers enough nitrogen to the crop to optimize yield and profitability while minimizing losses to water and air.
Applying nitrogen fertilizer to wheat Michigan State University Extension Article

Apr 2014

This Michigan State Extension research guide outlines single versus split nitrogen application rate recommendations for wheat. Best management practices are highlighted for application timing and fertilizer types.
Corn nitrogen recommendations Michigan State University Extension Article

Apr 2017

This Michigan State Extension research guide provides corn yield results with varied nitrogen fertilizer rates in continuous corn systems versus corn following soybeans.  The three main yield influencing factors were water availability; crop heat units and soil texture.
Manure’s Impact on Yield, Nitrogen, and Carbon Soil Health NEXUS Research summary

May 2018

Manure is often viewed by many as an environmental liability. However, if manure is applied at rates equal to or less than the nitrogen (N) requirement of a crop, can manure produce environmental benefits over commercial fertilizer?
Cover Crops for Soil Nitrogen Cycling Purdue University Fact sheet

Aug 2016

Cover crops can provide many benefits for soil and water quality and crop production. One of the important benefits of cover crops is their impact on soil nitrogen cycling. Generally we would characterize cover crops as either a scavenger of soil N or a producer of soil N, although legumes will do both.
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.
Soil Quality Indicators: Soil Nitrate USDA-NRCS Fact sheet

Jan 2014

Fact Sheet. Nitrate (NO3) is a form of inorganic nitrogen (N) naturally occurring in soils. Sources of soil NO3 include decomposing plant residues and animal manure/compost, chemical fertilizers, exudates from living plants, rainfall, and lightning.
Nitrogen Management Guidelines for Corn in Indiana Purdue University Extension Publication

Mar 2019

Report summarizes corn yield response to fertilizer nitrogen (N) rate in field scale trials conducted in Indiana since 2006. Results are applicable to N management programs that use efficient methods and timings of N fertilizer application.
Nitrogen Fertilizer Management in Good Economic Times and Bad Purdue University Extension Publication


Publication reviews how farmers can optimize nitrogen utilization in corn.
Optimizing Nitrogen Fertilizer Decisions Purdue University Extension Article

Feb 2001

Article examines how farmers can fine-tune their N application rate calculations and maximize the crop’s N use efficiency.
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.
Management of Nitrogen and Phosphorus SARE Governmental / Extension Webpage

Not Dated

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
Nitrogen Basics – The Nitrogen Cycle Cornell University Extension Fact Sheet


The nitrogen cycle describes how nitrogen becomes available to crops. Nitrogen breaks down and is released as different products, depending on what is present in the environment, such as soil microbes and crops.  Understanding this cycle will help estimate when nitrogen will be available, to maximize availability to crops and minimize nitrogen leaching which is a pollutant and an economic loss.
Managing Soils Penn State Extension Webpage

Aug 2012

The goal of good soil management is to meet essential plant needs for water, nutrients, oxygen, and a medium to hold their roots with as little management as possible.
Add-on Test: Potentially Mineralizable Nitrogen Cornell University Extension Publication

Mar 2017

The suite of soil analyses in the Cornell Assessment of Soil Health packages are all available as individual tests. Certain analyses, such as Potentially Mineralizable Nitrogen, are not part of the Basic or Standard packages but are available as add-ons or as individual tests.
Title Source Resource type and Date Short Summary
Wheat Tiller Number and Spring Nitrogen Recommendations Purdue University Extension Article


Article explores nitrogen recommendations for Indiana wheat.
Preplant Nitrogen Test for Adjusting Corn Nitrogen Recommendations University of Missouri Extension Webpage

Mar 2000

Information on why a soil test for nitrogen is important, and how to take these samples. Overapplication of fertilizer or manure nitrogen (N) in corn can cause water quality problems when unused nitrogen leaches into ground and surface water. Applying nitrogen according to crop need maximizes the economic benefits of applying fertilizer.
Soil Quality Indicators: Potentially
Mineralizable Nitrogen (PMN)
USDA-NRCS Fact sheet

Jan 2014

PMN can be defined as the fraction of organic nitrogen converted to plant available (or mineral) forms under specific conditions of temperature, moisture, aeration, and time. Determining levels of PMN can provide an estimate of available N in the soil.
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.
N Mineralization Potential – In Situ Buried Bags Michigan State University, LTER Extension/Research Protocol

Not Dated

Protocol to measure soil N mineralization potential using buried bags. The nitrogen mineralization potential of soils is an estimate of the net production of inorganic N under given conditions and provides a means to assess soil N availability.
Biodiversity Gradient: Baseline Soil Sampling Michigan State University, LTER Extension/Research Protocol


Basic soil sampling methods using cores. Used to measure inorganic N and soil moisture.
Soil Inorganic N Michigan State University, LTER Extension/Research Protocol

Not Dated

Protocol to sample inorganic N. Ammonium (NH4+) and nitrate (NO3) are the predominate forms of inorganic N in soils; their availability affects rates of N transformation, plant uptake, and N leaching.
MCSE: Soil Leachate – Inorganic and Dissolved Organic Nitrogen Michigan State University, LTER Extension/Research Protocol

Not Dated

Protocol to measure Soil Leachate. Soil leachate samples are collected from low-tension quartz lysimeters on a biweekly basis from March through November.
Yield stability analysis reveals sources of large-scale nitrogen loss from the US Midwest Nature Scientific Report

Apr 2019

Farmers can pinpoint exactly which spots in their fields produce stable yields as well as which areas are inconsistent. By concentrating on those, farmers can save money, reduce fertilizer loss, and lower greenhouse gas emissions. ​
Fate and Transport of Nutrients: Nitrogen USDA-NRCS Governmental Webpage

Sep 1995

This manuscript reviews the fate and transport of N from the various sources used to supply the N-requirements of crops in the context of the N cycle.
A Comprehensive Guide to Wheat Management in Kentucky University of Kentucky Extension Publication


Publication explores Kentucky wheat production, including nitrogen recommendations.

This page reviewed by Liz Schultheis, Mara Zelt, Mike KuceraGary Lesoing,  Kenny EckWalt Sell, Todd WhitneyNaeem Kalwar, and Vicki Morrone.

Technical review: April 13, 2020