Written by Mike Hamilton, CCA & President of Turf Dietitian
Environmental pressure and golfers’ expectations have fostered the need for superintendents to have a comprehensive understanding of nitrogen’s function within the plant, as well as its precise management.
I know most Superintendents are very responsible with the use of fertilizers and chemicals, but many home owners and other less qualified individuals aren’t. Unfortunately, the waters of the world are environmentally impacted by others’ lack of experience in applying nitrogen. That impact should be of great concern to you.
If some environmental groups had their way, they would completely prohibit the use of nitrogen on golf courses. You can bet that some environmental groups have already approached our legislators with such demands. The industry doesn’t need the fate of nitrogen fertilization to be used as a negotiating tool by legislators.
I’m not here to argue about whether or not nitrogen is polluting the Earth’s water as that is above my level of expertise. What I am here to advocate for is the need to continuously improve your knowledge, and to encourage you to make it your mission to use all fertilizers and chemicals as responsibly and efficiently as possible. Superior knowledge and professionalism give you the ability to shield the golf industry against unjustifiable allegations regarding the improper use of nitrogen.
The increasing demands on the part of our Golfers has led to the need for precise nitrogen management. Golfers continue to ask for faster, smoother, and more playable greens. Unfortunately, it’s not uncommon for your job security to be based on your ability to provide those conditions without damaging your plant’s health. As all of us know that’s not an easy goal to achieve. The only way to keep the turf health and give the golfers what they want is through precise management programs.
Low nitrogen levels can cause poor root growth, which in turn will cause insignificant uptake of water and nutrients. Lack of nitrogen can also lead to poor color, thinning turf, poor disease resistance, and intensified environmental stress. Put more simply: if you under apply nitrogen your turf will become sickly and probably die.
Over application of nitrogen to manicured turf can also cause life-threatening disease, major deficiencies of other nutrients, environmental stress, and a lot of sleepless nights for Superintendents. Therefore, it’s crucial that nitrogen is managed accurately.
I’ve always believed no matter how good a person is at their job, there’s always room for improvement. So how do you get better at managing nitrogen usage? Here is what you must know in order to assure you’re doing your best.
- Monitor the plant’s need for nitrogen at all stages of growth.
- Monitor nitrogen uptake and ingestion in the plant.
- Monitor plant health in relation to nitrogen levels in the plant during all growth stages.
- Monitor nitrogen’s effect on the uptake of other nutrients.
- Monitor nitrogen loss from the soil.
- Monitor nitrogen loss from the plant.
- Monitor nitrogen levels in the soil.
- Monitor nitrogen levels in the irrigation source.
- Determine how much nitrogen is released from soil organic matter
- Determine the ideal level of nitrogen in the plant, and only apply when levels are less than ideal.
- Have a complete understanding of the functions of nitrogen in a plant.
- Apply the most efficient source of nitrogen.
- Apply nitrogen at the lowest rate necessary.
- Monitor weather conditions before scheduling any nitrogen application.
That all makes sense, right? So, how do you determine when to apply nitrogen? That’s simple! Conduct water, soil, and plant tissue testing; along with the translation of all that data. By understanding where the N comes from, the levels of N in water and soil available for plant consumption, what source of N is present in the soil, how much N is in the plant, and how healthy the plant is, you will help to increase your expertise and efficiency.
Now the real question: Do you have the time to sift through all the data to determine exactly when and how much nitrogen to apply? Probably not. If you’re like most Superintendents, your plate is already full. However, that’s what Turf Dietitian is here for – that’s what we specialize in! Our goal is to be part of your team and assist you in making the most efficient and effective decisions for your nutrient management programs.
Choosing the Most Efficient Sources of Nitrogen
The application of the correct source is a critical component to any efficient nitrogen management program. Applying the same source of nitrogen for every application because it’s worked in the past can prove to be wasteful and can cause imbalances of other plant nutrients, which in turn can diminish plant health.
Depending on factors such as mineralization, volatilization, nitrification, and denitrification, the form of nitrogen in your soil can change frequently. Weather has an enormous impact on the fate and the transformation of nitrogen in the soil. Unless you have a crystal ball, the only way I know to identify the amount and structure of nitrogen in the soil is to have soil reserve and soil solution tested at least 4 times per year in the south and 3 times per year in the north. (Spring, Summer, Fall, and Winter for warm season grasses).
You’ve all seen the chart that shows if a nutrient is a cation or anion. You also know that nitrogen is both and is taken into the plant as an anion (NO3-) and cation (NH4+). Not only is proper nitrogen management dependent on the NO3 to NH4 ratio, but also total nutrient management.
Why is the ratio between NO3 and NH4 so important to nutrient management and plant health? Because even in this day, crowded with designer nutritional products, the most effective way to carry nutrients into the plant is with nitrogen. Cations attach to NO3 and anions attach to NH4, because opposite charges attract. Given that the plant requires large amounts of nitrogen, it will collect all it can through the mass flow of nutrients located in the soil solution. When the nitrogen goes into the plant, the nutrient that is attached goes along with it.
In reading many articles on this subject, the best I can determine is that ideal NO3 to NH4 ratio in turf is 3 to 1. Why? Because cations are used by the plant in a higher quantity (about 3 to 1) to complete all its metabolic functions. If NH4 is high in soil solution it is likely the plant will not take in enough cations. Conversely, if the NO3 is high in solution, the plant most likely will not take in enough anions.
Nitrogen (N) is the key component for growing and sustaining the turf and plants on your property. This essential nutrient makes up the core element of most plant structures and the internal and external metabolic processes. So, what does this mean for your golf course? The turf on your golf course can’t live without nitrogen.
Plants have one purpose on this Earth, to produce proteins and oxygen so that animal life to exist. Nitrogen is responsible for almost every process that converts light energy into plant proteins.
Known as the backbone for plants, nitrogen ensures that your plants experience strong and healthy growth. Nitrogen is the nutrient that is used most by all plants and is essential for almost every metabolic and plant defense function. Given its significant influence on your plants’ health, it’s easy to over or under apply nitrogen. Thus, it’s vital that Superintendents monitor the nitrogen content present in their soil and plant, in order to ensure the plant is getting what it needs at all times.
The wellness of your plants depends on the availability and precise use of nitrogen. Understanding the basic process of nitrogen behavior in soil may be complex, but it will make your life as a Superintendent that much easier.
This biologically influenced process is, in turn, influenced by climatic conditions. The location and soil composition of your golf course has an enormous influence on the biology of the system. The climate will also have an influence on how nitrogen behaves within the soil. It’s important that you get to know your soil in order to be prepared for climatic changes.
Trust me, the more articles I read and learn about plant physiology, the more I am amazed by the complexity of plants’ cellular development. Each plant is made up of their own molecular structure that needs to be nurtured. However, most of the members I’ve dealt with have difficulties getting into the nitty-gritty science behind plant growth.
Think of it like this: your turf is a living organism, just like you. As you need food and water to survive, so does your turf. Getting to know your plants and what they need will help you keep a healthy turf
Nitrogen’s Primary Roles within the Plant:
To start off with, let’s look at the role nitrogen plays in your plant’s structures. Nitrogen is a key nutrient fo the health and development of your plants. A few reasons for this are:
Nitrogen makes up the plant structure’s amino acids – these are the building blocks of plant proteins. Plant proteins ensure healthy germination and development of vital plant tissues and cells like the cell membranes and chlorophyll.
- Nitrogen aids in the plan’ts survival and helps form the plant’s DNA material.
- Nitrogen aids with photosynthesis and enhances the plant’s color.
- Nitrogen is vital for healthy growth and development.
- Nitrogen is a component of amino acids, proteins, vitamins and enzymes.
Where Nitrogen Can Be Found:
We all know you can get bags of manufactured nitrogen from your local fertilizer distributors. However, many times we ignore the most basic supplies. It’s imperative that you’re utilizing the right amounts and embracing the natural supply of nitrogen in your soil.
On many occasions there is enough nitrogen released form soil organic matter during the growing season to supply much of the nitrogen that the plant needs. Yet, most fertilizer suppliers developed programs that encourage applications of liquid forms of nitrogen weekly. My question to you is, how does a supplier know your plant needs nitrogen every week of the growing season? There is no possible way! Unless they are conducting a detailed analysis of each and every factor involved in the plant’s uptake and usage of nitrogen weekly.
Natural Nitrogen Sources:
Manures and Organic Waste: I’ve found that the use of natural organic fertilizers in the golf industry is divided down the middle. There seems to be two basic points of view on whether organic fertilizers are used or not used by Superintendents. Some Superintendents believe that they are trying to prevent and reduce organic matter in their soils, so applying organic material only adds to the problem. Other Superintendents believe that organic fertilizers increase microbial activity in the soil, which helps to improve soil structure and reduces plant stress.
My personal belief is the only bad thing about using organic sources, is the release of the nutrients from the source is unpredictable. However, that is true with all slow release sources. The reality is, that no matter which philosophy you support, monitoring is the only way to determine the release and usage of nitrogen by the plant.
Clipping residues: Another source of nitrogen is in clipping residues. Although very few golf courses return clipping on greens, I do recommend doing it whenever possible. Despite existing in relatively small amounts, the clippings will help nourish both your turf and soil.
Clipping removal is not the only way that you may be disrupting the nitrogen flow in your golf course’s soil. Soil migration and runoff play a role, too. These may not be the main contributors to decreased nitrogen levels, but they should be taken into consideration when you’re planning your water surface management.
I’d recommend developing a fertilizer program to help protect your course against nitrogen loss through erosion or runoff. Typically, the best programs I see are made of a combination of bulk applications of slow release products during aerification, and liquids to supplement when needed.
Soil organic matter: We’d recommend developing a fertilizer program to help protect your course against nitrogen loss through erosion or runoff. Typically, the best programs I see are made of a combination of bulk applications of slow release products during aerification, and liquids to supplement when needed.
You know by supplying oxygen to a soil, organic matter decomposes quickly. However, it leaves behind a more resistant residue that we call humus. This portion of organic matter releases about 20 to 40 pounds of nitrogen per acre per year for each percentage of organic matter. It’s a much slower and more constant release of nitrogen into the soil.
Other inputs of N for plant growth include:
- Biological fixation
- Atmospheric fixation
- Commercial fertilizers
As we’ve discussed, nitrogen has been known to change or transform its behaviors quite quickly. These changes influence the availability of nitrogen for the plants.
Mineralization: The conversion of organic N that’s present in soil organic matter, crop residues and manure into inorganic nitrogen is called mineralization. Through this process, bacteria is digested in the organic material and ammonium is then released.
Nitrification: The conversion of ammonium into nitrate. Nitrification proceeds more rapidly in warmer, more moist soils that are well aerated.
Denitrification: This is the process by which the converted bacteria that is now N gas is lost in the atmosphere. Denitrification will take place in soil that is ample in organic matter and waterlogged. It should be noted that this process is generally kept to topsoil.
Immobilization: A process that occurs when there is nitrate and/or ammonium present in the soil and it’s used by the growing microbes to build proteins. Think of it as a shot of steroids that helps you build up to be big and strong.
During this period, there’s a net gain of N during the growing season. This is due to the additional N present in the residue after the immobilization-mineralization processes.
Once you understand this cycle, you will be better equipped to see what your grounds need during the different stages.
Your Nitrogen Cycle Cheat Sheet
Nitrogen loss from the soil system
To fully develop a plan of action to prevent a loss of nitrogen, we have to back up and look at the cause. The loss of nitrate is a physical event and is referred to as leaching. This process involves the loss of NO3–N when it moves through the soil with excess water below the root zone. To simply put it, knowing your soil could make or break your soil system.
Each golf course has different types of soils with different functions. Coarse-textured soils are known to have a lower water-holding capacity, which has a higher potential to lose nitrates.
Different types of soil also have different water holding capabilities and play a role in how your soil is keeping irrigated too. Your soil’s nitrogen can be filtered if irrigation moves water straight through the root zone. If it moves past your root zone, your plant can’t benefit from nitrogen nutrients.
Denitrification can occur and cause a loss in NO3–N when water saturates the soil for two or three days. Superintendents can take comfort in knowing that nitrogen in the NH4+-N form isn’t subject to this loss.
Volatilization, on the other hand, can cause significant losses too. Volatilization occurs when nitrogen is lost as ammonia gas. The loss of ammonia gas is caused by levels of pH. Urea can be found in manure and fertilizer and is the stimulant for the ammonia gas process. Incorporating nitrogen into your manure and fertilizer will help eliminate the volatilization loss.
Nitrogen loss from volatilization is greater when:
- Levels of pH in the soil are higher than 7.3
- There’s a higher air temperature
- Moisture is rich on the soil’s surface
- The soil is rich in residue
To recap, here are the main factors contributing to nitrogen loss in the soil system:
- Crop Removal
- Soil erosion and runoff
- Improper amount of N applied
- Carbon-nitrogen ratios greater than 20:1
The nitrogen cycle is biologically influenced. Biological processes, in turn, are influenced by prevailing climatic conditions along with a particular soil’s physical and chemical properties. Both climate and soils can vary greatly across your golf course and affect N transformations for the different areas.
Nitrogen Deficiency Symptoms
Now that we’ve looked at the causes, we can start to identify when your plants are taking a turn for the worst:
- The plants’ petioles and veins turn a light red
- Older leaves will gradually change from their normal, healthy green appearance to a much paler green. They will become more uniformly yellow as the deficiency progresses.
- If your leaves turn a yellow-white color, they might have an extreme deficiency.
- Younger leaves tend to become smaller in size and have a paler green color to them.
- Your plants are shorter due to a reduced branching effect.
- The leaf’s veins will turn yellow along with the whole leaf’s appearance.
- A reddish or purple color can be found on the underside of leaves and petioles.
- You will start to notice that older leaves will wilt under water stress much sooner than before the deficiency progressed.
Luckily, the recovery of deficient plants to applied nitrogen is immediate and spectacular.
Nitrogen Antagonism and Interaction
- Levels of micronutrients can become deficient when there are high levels of nitrogen. This is caused by accelerated growth rates.
- An excess of nitrogen dilutes the Phosphorus, Calcium, Boron, Iron and Zinc elements.
- The uptake of Phosphorus, Calcium, Boron, Iron and Zinc can be reduced by low soil levels.
- In order to make Molybdenum deficiency appear less obvious, you can use Ammonium Nitrogen.
Key points for Superintendents
I hope for extensive transformations and reactions of nitrogen in the soil. Were you expecting it to be so complex? Keep it simple and focus on these major points:
- Plants only take to inorganic nitrogen, even though you can add both organic and inorganic nitrogen forms to your soil.
- All nitrogen sources can be converted to NO3-N
- Identifying the initial source of nitrogen is impossible once it’s in the plant or water supply.
- Nitrate will move with your soil’s water and will always be present in the soil solution
- Your plant uptake can be increased as a result of inhibiting the conversion of NH4+-N to NO3-N. Less nitrogen can be lost too. As a superintendent, you should keep sound management practices in place to help prevent the NO3-N from getting into the water supplies.
- You must test soil, water and plant tissue as frequently as possible to precisely manage nitrogen needs by the plant.
Common Nitrogen Sources
Sulfur Coated Urea
25-0-0—-19% Calcium—-1.5% Magnesium
3% to 10% N