Nitrogen (N) Sources
For Lawn Fertilization

Nitrogen is an essential element for a beautiful lawn. However, with today’s concerns about a healthy environment, more attention is being focused on the types of fertilizer and sources of N being used. Choices range from natural organic and synthetic organics to inorganic sources of N.

Unfortunately, there is a lot of misinformation associated with all these products. When products are used properly, the grasses root system is highly efficient, trapping most nutrients and even pesticides before they can leach past the root zone.

However, the different choices we have are actually good for us, if we possess the knowledge of when and how to use them properly. For a better understanding of environmental issues, see the page on the Effects of Pesticides and Fertilizers on the Environment.

Most Lawn fertilization programs are based on the nitrogen element. This is because N is the element grasses use in the greatest amount. N is essential in almost all plant functions, especially in energy and chlorophyll production.

Insufficient N affects grass' ability to produce carbohydrates, the plant's food source. If the soil is depleted of nitrogen, the grass will suffer and could eventually starve to death. This page will give you a view of specific N sources that are available and how they can benefit your lawn.

Natural Organic Sources of Nitrogen

The Two Primary Catagories of Organic N Sources

Organics are rapidly gaining in popularity in many places around the world, including the U.S. While many excellent fertilizers are available, many of the better ones are available only to professional companies.

Organic fertilizers can be divided into two different categories:

1) Natural Organic 
2) Synthetic Organic

Natural organics are what most people think of when the subject of organics is discussed. They include fertilizer derived from animal and plant by-products. With natural organics, the N can only be released by activity from soil microbes.

The name "synthetic organic" may sound like an oxymoron, but it actually isn’t. Synthetic organics are classified as an organic because they contain carbon in their structure. In fertilizer, “carbon” (C) is a term that is applied to organic matter.

Natural Organics

Organic fertilizers are an excellent source of nitrogen and have been used since ancient times. Their primary limitation is that they must rely on soil microorganisms to breakdown the organic matter into substances that can be taken up by plant roots. The amount of nitrogen released varies with the material used, but as a rule, the N content is low, measuring less than 1% and rarely higher than 10%.

The important thing to know is that microorganisms are dormant during cold weather and are most active in peak summer months. Most soil microbes become active as soil temperatures reach 55 degrees. This means you cannot expect any reaction from natural organics when applied while microbes are inactive, regardless what the manufacturer or salesman may tell you.

The exception is with certain "bridge products". Bridge products are natural organics blended with synthetic organics or inorganic nitrogen sources. These fertilizers give you the best of both worlds with slow release N in the form of organic matter and faster release sources of N as well.

Natural organics excel in summer. In areas where weather is warm for most of the year, organics can be used throughout that time. Burn potential is low and can be spread at heavy rates.

These products release nitrogen very slowly making over-fertilization difficult. An additional benefit is that some types provide numerous micronutrients as well. Natural organic fertilizers include sewage-based materials, animal manure and plant by-products.

Sewage-based Products

Sewage-based products, as the name sounds, are made from human waste derived from sewage treatment plants. Sludge from waste treatment plants have been commercially used as fertilizer for about 75 years. Materials have been heat treated to kill all bacteria, dried and then granulated for easy spreading. It has a slight organic odor, similar to most manure fertilizers. The drawback is the low nitrogen content, generally around four to five percent.

The one concern in using sewage products is with heavy metals. The micronutrients Boron (B), copper and zinc are higher in these materials. However, regulations require it to be monitored and cannot exceed certain levels.

Popular brands include Milorganite and Huactinite.


Animal manure has been used as fertilizer as long as people have been growing plants. The nitrogen content of manure varies, but is generally low.

Cow and horse manure are not usually made into granulated fertilizers because of the low N content.

One of the goals of manufacturers is to use materials with substantially higher nitrogen content, so it can be spread at rates similar to other fertilizers.

Commercial manure or animal by-product fertilizers are commonly made from chicken and turkey litter, blood meal, poultry feathers, leather by-products and other animal products. These products can be applied at any time of the year, but will only be effective during the warmer months when soil microbes are active.

Cow and horse manure is better used for soil modification. It is best when roto-tilled into the soil before planting, but can be spread over the lawn as a top dressing when properly processed.

It is a common practice in rural areas to get unprocessed manure straight from barns or pastures. You can do this, but be aware, you may also get a lot of weeds and wild grasses as well. Whatever the animals were eating could grow in your lawn and garden.

You should not use manure that is less than 6 months old. Since lawns are not being used for humans consumption, it is acceptable for use if it is unprocessed, but should not be used in vegetable gardens. There may no telling how old the manure actually is and there is always a possibility it could still contain harmful bacteria.

Natural organics made from manure or animal by-products include Ringer products, Toro BioPro, Nature Safe and Nutrients Plus.

Nitrogen from plant and animal by-products

Plant fertilizers are mostly by-products derived from grain mills and will deliver up to 10% nitrogen. They are safe to use on lawns, but many manufacturers market only to the professional industry. An example is a company called "Nature Safe".

Nature Safe has been producing natural and organic fertilizers for the professional industry since 1943. However, with the home lawn industry seeking natural products, more products are becoming available. A leading fertilizer that is available for home use is corn gluten meal.

Corn Gluten Meal is a product that is marketed as an organic fertilizer and a pre-emergent weed control as well. The best weed control qualities are reached after a couple years of application. One of the drawbacks is the amount needed to work effectively. The first time you use corn gluten, especially for its pre-emergent effect, the recommended rate is up to 20lbs per 1000/sq.ft.

Manufacturers include Dynaweed, ProPac, Suppressa, and Wow! as well as others. You can also purchase it though many local farm and feed stores. Renaissance is another product that is made from Soybean protein.

Synthetic Organic Sources

Nitrogen derived from synthetic organic sources are the most commonly used types in fertilizer. "Synthetic organic" may sound a bit like an oxymoron, but it isn’t. Although it is chemically based, it contains carbon in its structure, which classifies it as an organic.

Water Soluble Nitrogen 

Urea is the primary source of N used in synthetic organics. Urea is very versatile and can be used in liquid formulations as well as granular. Quick release urea N dissolves rapidly when water is applied and is sometimes listed on the bag as “WSN” or Water Soluble Nitrogen.

Water Insoluble Nitrogen

Urea can also be altered through chemical reactions with other chemicals forming slow release forms of nitrogen. These are referred to as “WIN” or Water Insoluble Nitrogen. Different slow release products will have different release rates ranging from several days to several weeks. Slow release products that are produced from chemical reactions with urea include ureaformaldehyde (UF), isobutylidine diurea (IBDU and triazone. You will often see one or more of these nitrogen products listed on fertilizer bags along with the percentage of each ingredient they contains.

Encapsulated Nitrogen

Slow release forms of N are also formed when urea is encapsulated in materials such as sulfur (sulfur-coated urea or SCU) or a plastic called polymer (polymer-coated urea or PCU). Just like the chemically altered urea, the encapsulated urea breaks down in the presence of water.

Depending on how the urea was altered will determine the degree of slow release. Some products could take as long as two or three weeks to begin releasing N. Fertilizers containing slow release ingredients will generally contain a percentage of quick release N (WSN) to provide green-up until the slow release N kicks in.

Two important things to know and to remember: 1) is that the soil needs to receive moisture for the fertilizer to release. If the ground is allowed to dry too much, the release action will stop.

Nitrogen Release REQUIRES Microbial Action

2) Ureaformaldehyde and triazone must also have microbial activity to release N into the soil. Yes, you guessed it. It means that those two N types work best during warmer weather when microbes are more active.

Nitrogen Release DOES NOT Require Microbial Action

Isobutylidine diurea does not need any microbial activity to release the nitrogen. Just something to think about if you are planning to use last year’s summer fertilizer in early spring.

A note about "bridge products". Bridge products contain organic matter combined with synthetic organic or inorganic sources and were developed for year around use.

Early spring bridge products will contain the least amount of organic matter due to low microbial activity. For the required nitrogen needs, they are supplemented with the right N sources necessary for that time of the year.

Summer fertilizers will take advantage of the high microbe activity and can be very high in organic matter. Fall fertilizers are also high in organic matter, but are fortified with higher nitrogen sources necessary for fall fertilization of cool season grasses.

These fall fertilizers are also good for warm season grasses the require more nitrogen during peak summer growth.

Inorganic Sources of Nitrogen

Inorganic sources of N are probably the best known types of nitrogen. This group consists of ammonium nitrate, ammonium sulfate, calcium nitrate and potassium nitrate. Their low cost is a big reason for their popularity.

Reasons for Inorganic Nitrogen Sources

Some plants that have had disease problems will respond better with Ammonium Sulfate. Bermuda Dead Spot, will grow out of it better using this nitrogen source. Other N sources can inflame the disease. 

Most of the better fertilizers will contain some of these N sources, but often in small amounts. They are mixed with slow release forms of N to give an immediate response while waiting for the slow release fertilizers to begin working. However, you can buy fertilizer that contains one of these inorganic nitrogen sources as the only source of N.

The problem most homeowners will face with these N sources is their high burn potential and quick release. Applying too much will cause excessive surge growth, which is not healthy for turfgrass.

The fertilizers can burn the grass, regardless of the amount applied, especially if too little water is applied. If the fertilizer bag lists an inorganic N source as it main N ingredient, it will need to be applied very carefully and watered in thoroughly after applying.

Additionally, the warmer the air temperature is, the greater the burn potential becomes. As the N releases, what is not absorbed by plant roots will likely leach below the root zone. When people think of environmental problems with fertilizers, it is often the inorganic sources of N they are referring to.

Other Sources of Nitrogen

Lawn Grass Clippings

Lawn grass clippings are one of many sources of N that can lower the need for fertilizer by as much as 25%. Leaving the grass clipping on the yard instead of bagging them actually benefits the grass in a number of ways and is one less thing going into our landfills.

A blade of grass is 80 to 85 percent water. As the grass blade decomposes, it releases N back into the soil. Like other slow release sources of N, grass clippings can take several weeks to several months to completely break down. The greatest release of N will be in the summer, due to faster desiccation and higher microbial activity.

An important rule to consider with lawn clippings is the "one third rule". This rule has to do with the relationship of mowing and grass health, which states that we should not remove more than one third of the grass blade at a time. Using this rule, the grass clippings are smaller and break down faster. Also, try not to mow your grass when it is still wet. Wet grass clogs the bottom of the mower and leaves unsightly clumps on the yard that take longer to break down.


Leaves that drop in the fall, like grass clippings, will release some N and add organic matter back into the soil as they break down. For best results, the leaves need to be finely mulched. Mower decks designed for mulching are best, but any type of lawn mower deck will work. It your mower is designed to throw the grass clipping out to the side, it may require more than one pass over the leaves to mulch them properly. Using a mulching blade will shred the leaves faster and more efficiently.

However, there shouldn’t be an over abundance of leaves. Too many leaves, even when mulched, can form a thick layer over the soil. This layer can mat forming a barrier that can hinder moisture from reaching the roots. Another problem is with the cooler weather. By the time all the leaves have fallen, the soil temperatures have cooled and microbial activity will be much lower. Without active mircoorganisms, nutrient benefit to the lawn will be delayed.

If you have a garden area, the leaves can be mulched and roto-tilled into the garden.

Developing a Lawn Fertilization Program

Behind every beautiful lawn is a good lawn fertilization program. Whether it's a championship golf course or your home lawn, certain fundamentals always apply. Click here to see how to plan your fertility program.

How to Collect a Soil Sample

The first step in understanding what is in your soil is to take a soil sample. Click here to find out how to how to collect a soil sample that will deliver the best results.

Understanding the Soil Analysis Report

Understanding the soil analysis report can be difficult. Click here for an explanation of results commonly found of most reports.

Simple Formulas for Calculating Fertilizer Rates

One of the difficult parts about fertilizing is knowing how much to put down. This page gives you simple mathematical formulas for determining the correct amounts in different situations.

Spreader Calibration Made Easy

Spreader calibration made easy! Knowing if your spreader is actually putting down the right amount is important for professionals and homeowners alike. This page offers all you need to know about calibrating your broadcast or drop spreader.

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