Written by Mike Hamilton, CCA & President of Turf Dietitian
Because of that century and a half old Liebig’s Law, we know that every nutrient is equally essential for plant health. However, when you look at nutrient’s functions, some simply do more work than others.
So how important is phosphorous? If there were no phosphorous there would be no life on this Earth!
Phosphorus appears in all plant, animal and microbial cells. In plants, phosphorous is imperative for collecting the sun’s energy and completing the photosynthesis process, by converting it into plant energy that is utilized for cell development and reproduction. In plants, phosphorous is a fundamental part of metabolic processes such as photosynthesis, energy transfer, energy synthesis, breakdown of carbohydrates via adenosine triphosphate (ATP). Phosphorous is also a part the formation of ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and membrane phospholipids.
Phospholipids act as both fat-soluble and water-soluble complexes. Phospholipids can be immediately absorbed or dissolved in cellular water. Phospholipids can also be hydrophobic and form fatty acids. The combination of both characteristics makes it easy for phospholipids to transport materials like proteins and lipids, and maintaining the structure of plants.
So, all you need to do is regularly apply phosphorous and your turf will be fine, right? Not so fast my friends. Every environmentalist in the world would condemn you for frequently applying phosphorous. There are environmental associations that are trying to get our government to pass laws banning the use of any phosphorous for plant growth. In my opinion that thought pattern borders on stupidity and should be contradictory for any logical person. Phosphorous can indeed pollute water sources, but only if over applied or directly applied to a water body. Responsible superintendents are not part of phosphorous pollution.
The majority of the fertilizer ordinances that I have read, have blackout periods during rain seasons (in most cases growing season). Most ordinances state that golf courses are exempt from these blackouts, but only if you can prove a need. I see very few soil reports that show phosphorous as being deficient in the soil. So based on soil data, you will have a difficult time proving a need.
You are fortunate at this time, as I’m not aware of any state that’s enforcing the existing ordinances. However, you should keep in mind that most environmental laws are either enforced or not enforced due to political majorities. Even if your local government does start enforcing fertilizer ordinances, you have a loophole if you need to apply phosphorous; it’s called tissue testing.
We’ve analyzed hundreds of thousands of tissue tests and they frequently show phosphorous deficiencies in the plant. Why? Because, very little phosphorous is available for plant uptake. Phosphorus becomes plant available as minerals weather, or by microbial degradation. The problem is rainwater isn’t acidic enough to mineralize phosphorous from soil particles, and microbes have to work hard to break the strong bond.
Fortunately, tissue testing is inexpensive, current, and the data can be used to prove phosphorous deficiency within the plant. I cannot put any more emphasis on this statement other than this bold print. Every time you apply phosphorous you should attach your proof to the application sheet, regardless if it’s a spray or granular application. Why? If the government begins to strictly enforce fertilizer ordinances, and they find no proof for application, they will start digging in deep to your records. No one wants that to happen.
Proving a need if you apply phosphorous is as easy as a phone call away. Give Turf Dietitian a call and we will help to protect you and your club from enforcement.
Another way to prove you are being proactive is to show an effort to lower the high levels of phosphorous in soil reserve. There are a few ways you can speed up the mineralization with chemical applications.
You can apply low rates of a strong acid (pH less than 5) to mineralize strong bonds, and release tied up phosphorous. Some will leach, but much of it will be available for plant uptake. Keep in mind though, when the plant dies or clippings are returned to the soil, very little of that phosphorous will leach out of the soil; it too will tie-up. Therefore, lowering excessive phosphorous levels will be a slow process, especially if there are high levels in the irrigation, or rainwater. Also, research the acid you use, some create long term problems that can damage soil structure.
Calcium chloride can help to lower P levels in soil reserve by producing Calcium Phosphate. Once calcium bonds with phosphates, it will slowly leach through the soil. CaCl2 dissolves in water, producing chloride and the aquo complex [Ca(H2O)6]2+. This process is slow, but effective if you use CaCl with a water flush.
3 CaCl2 + 2 PO3−4 → Ca3(PO4)2 + 6 Cl−
If your soil has a lot of natural calcium chloride, there is a good chance your levels phosphorus will be low in soil reserve.
(This has nothing to do with this article, but it’s a pet peeve for me. There is no such thing as an insoluble compound. Everything can be broken down; it just depends on strong acidity and time.)
Why is phosphorous so important to life? For all my customers who are sick of hearing me say apply phosphorous because the plant is running out of energy, here is why:
1. Phosphorous provides energy to the plant by using the energy from the sun to help complete the photosynthesis process
2. Phosphorous is part of the molecule adenosine triphosphate (ATP) which produces energy.
3. ATP also transports energy within cells and is the main energy source of the cell and the Krebs Cycle.
4. ATP is the central energy source for the bulk of cellular functions. This includes the synthesis of macromolecules, including DNA, RNA, and proteins.
5. The Krebs cycle is the world’s smallest biological motor.
6. The Krebs cycle is a part of cellular respiration. The Krebs cycle delivers the hydrogen and electrons needed for the electron transport chain (ETC).
7. Cellular respiration is what cells do to break up sugars so plant cells can use it as a food source. Cellular respiration uses the food to generate the ETC.
8. The electron transport chain happens in the mitochondrion which is the site where succinate generated in the Krebs cycle are oxidized, providing energy to power ATP synthase. ETC is also responsible for cellular respiration.
9. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen are derived from the amino acids adenine, thymine, guanine, and cytosine. The order of these bases is what determines DNA’s instructions, or genetic code.
10. RNA is any of a class of single-stranded molecules transcribed from DNA in the cell nucleus or in the mitochondrion or chloroplast, containing along the strand a linear sequence of nucleotide bases that is complementary to the DNA strand from which it is transcribed: the composition of the RNA molecule is identical with that of DNA except for the substitution of the sugar ribose for deoxyribose and the substitution of the nucleotide base uracil for thymine.
11. Amino Acids are the building block that make up proteins. Each amino acid has the same fundamental structure, which consists of a central carbon atom, also known as the alpha carbon, bonded to an amino group, a carboxyl group, and to a hydrogen atom. Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group,
12. Proteins are polymers of amino acids. Proteins have a variety of function in cells. Major functions include acting as enzymes, receptors, transport molecules, regulatory proteins for gene expression, and so on. Enzymes are biological catalysts that speed up a chemical reaction without being permanently altered. They have “active sites” where the substrate/reactant binds, and they can be either activated or inhibited.
Each of these bullet points could be expanded into a very large book or a lifetime of work for a scientific researcher. I admire people who devote their entire careers to understanding plant metabolism, but it’s way more analytical than I’m able to be. The one thing you need to take away from this outline, is that none of these fascinating chains of events could take place without phosphorous. Also, there are people who want you to stop using life sustaining phosphorous.
As we have just read above, phosphorus is an enormously important macronutrient for plant growth, health and development. Although P is usually found in abundance in most soils, it is rarely in the plant available form for plant uptake.
Phosphorus is immobile in the soil and therefore the plant must form a deep root system to enhance phosphorus uptake. Plus, in most cases the available phosphorus is quickly pulled into the root leaving the immediate area around the root devoid of phosphorus.
The function of Phosphorus in the plant:
- Structural component of ATP (ATP is the trigger for the Krebs Cycle).
- Reproduction – structural component of proteins, amino acids, enzymes, nucleic acids, and DNA.
- Photosynthesis – production of sugars and starches.
- Respiration – producing energy by oxidizing sugars and starches.
- Energy production, storage, and transfer.
- Cell division and enlargement.
- Early root formation and growth.
- Greater flowering and seed production.
- Increase water use efficiency.
- Better cold tolerance.
Phosphorus Uptake by Plants
Phosphorus must be in the orthophosphate form for plant uptake entering through the root by diffusion.
Most of the Phosphorus that enters the root gets there via diffusion with a very small amount entering due to mass flow. There must be a higher concentration of phosphorus in the soil than in the root in order for kinetic energy to create a balance of available P. Because P is mainly insoluble, plants use phosphorus at a faster rate than it can be replenished.
High phosphorus soils are not immune from problems, as it can have a negative effect in the uptake of certain micronutrients. Phosphorus will often bind with zinc and/or iron converting them to a non-available form, making all three elements unavailable for plant uptake.
Phosphorus uptake can also be minimized by the following factors
- Strongly acidic (pH 5.5 or less) or alkaline (pH 8 to 8.5) pH.
- Sodium: High levels of sodium can affect the mineralization of phosphorus making it less available for plant uptake.
- Low Soil Organic Matter: The amount of organic matter in soil acts as a reservoir for phosphorus. The lower the OM, the lower the levels of phosphorus will be.
- Soil Temperature: Cold soil will cause a slowing of the mineralization process.
- Low levels of Mycorrhizae: Mycorrhizae are soil fungi that attach to plant roots and help transport nutrients to the root as well as helping absorb the nutrients.
- Compaction: Compacted soils often have low oxygen levels which will slow the release of phosphorus into the plant available phosphorus.
Phosphorus toxicity rarely occurs but problems can arise if phosphorus is over applied. The biggest concern is runoff, phosphorus can move with water and/or soil draining into bodies of water after heavy rain events.
There are many products available to help superintendents manage and prevent any phosphorus deficiencies and monitoring your soil through testing will help to find the most efficient product for your needs.
Phosphorus Deficiency Symptoms
With phosphorus being the main energy source for the plant, it stands to reason that one of the first symptoms of a plant being deficient in phosphorus would be a plant that is dwarfed or stunned. Mild to severe deficiencies of phosphorus will cause the tip and leaf margins to turn a purplish color before senescence will start to occur if deficiencies are not corrected.
Choosing the Most Efficient Method of Phosphorus Management
I cannot stress this enough; plant, soil and water analysis are a key method to maintain turf health. Even more so for analyzing the amount of phosphorus in the soil and the amount that is available for immediate plant uptake in the soil.
By doing more frequent monitoring of plant tissue, soil and water, it will allow you to be proactive to seasonal changes, and more efficient with your applications.
Correcting any nutrient problem is difficult, but it becomes easier when you understand how they behave throughout the year. It’s hard to correct problems if you don’t know what they are in the first place. Regular testing gives you solid data to make the best choices for your turf.