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Foliar Nutrition of Turfgrass |
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When discussing foliar applied and absorbed nutrients several concepts need
to be clarified. The first concept one needs to understand is that the “non-root” parts of plants can and will take up nutrients from nutrient sprays and other applications. This concept has been shown over a long period of time by many
researchers.
The second concept to discuss is the difference between fertigation, foliar applied fertilizers and foliar absorbed nutrition.
Fertigation is the application of small amounts of liquid or dissolved fertilizer through the irrigation system. The main advantage of this application technique is that relatively inexpensive inorganic fertilizers can be applied, often in small
amounts. This method keeps only what nutrition the plants require for short periods of time in the root zone. It is seen as an alternative to slow release fertilizers, which do the same thing. Both methods are environmentally sound since they prevent soluble nutrients from leaching below the root zone. The drawbacks to fertigation include: The need for a highly effective irrigation system, access to dealers who sell the bulk liquid fertilizer or the equipment
to make it, and the fact that some climatic zones do not require irrigation on a steady basis throughout the growing season. While very small amounts of nutrients may be taken into the plant direct, nutrients applied by fertigation are
still root uptake and should not be confused with foliar nutrition.
Another method of applying small amounts of nutrients to the turf, sometimes referred to as spoon feeding, is to dissolve the inorganic, powered fertilizer in water and apply with your spray tank, then water in. The advantage to this
method is that you can make even distribution of very small amounts of fertilizer that would not be possible to do with granular fertilizers. Again,
although the plants may absorb small amounts of these compounds, it should not be confused with foliar nutrition. The advantages of this method are similar to fertigation and slow release granular fertilizers. The main disadvantage to this method is that many of the inorganic soluble compounds can be phytotoxic
and cause burn of the foliage if not neither properly applied nor watered in. When compared to other forms of foliar nutrients that contain usable carbohydrates present to help with plant growth, several researchers have
shown that plants have the ability to absorb some forms of carbohydrates directly and utilize them for plant bio-functions. These various forms of carbohydrates are not present in the inorganic solutions of fertilizer.
Foliar Nutrition
Foliar absorption of mineral nutrients by above ground plant parts including leaves stems and flowers have been reported for over 200 years. Interest however has been mainly since the 1950’s. This interest has grown over the years because of the increased costs of fertilizers, environmental concerns about leaching and runoff, a better understanding of how to facilitate the absorption process and a better understanding of plant growth. Minor element
deficiencies in fruit have been corrected by foliar applications for 80 to 90 years. More recently over the last 40 years or so, foliar absorption of the macronutrients has also been studied extensively. It is now known that not
only nutrients can be absorbed but also pesticides, growth regulators, organic acids and many carbohydrates.
Among the advantages to foliar absorbed nutrients include the fact that they can be rapid and effective, with quick plant response. Because they are so effective they require less fertilizer input by avoiding soil fixation, leaching
and runoff. They are applied to the leaf blade and allowed to remain there until fully absorbed. You do not water in and no fertilizer is carried into the soil. Today we have the knowledge of how plants grow in order to make the most
effective use of this technique. Other advantages revolve around the fact that they are effective when the turf has a restricted root system from such things as being closely mowed, periods of environmental stress, seasonal root loss, periods of low photosynthetic output and correspondingly low carbohydrate reserve.
In turf unlike agriculture the plants are continually mowed. This continual loss of leaf blade creates the main disadvantage of foliar fertilizers on turf. Due to the constant mowing they need to be continually applied. However, this spoon-feeding is the best method of application, even if we were not removing the blade constantly.
Some nutrients including phosphorus become fixed in the soil and results in low efficiency as a root absorbed nutrient. Foliar applications of the macronutrients as a supplementary fertilizer are highly effective. Foliar application of micronutrients can be and have been used successfully for deficiencies in turf. Another advantage of foliar applied nutrients is that in wet climates the highly soluble nutrients such as nitrogen and potassium cannot be leached from the plant once absorbed, as they can be from the soil.
Factors that affect foliar absorption.
Several factors will affect foliar absorption include relative humidity, temperature, pH of the nutrient solution, variety of the turf, age of the leaf, concentration of the nutrient solution, difference in the nutrient compounds
(formulations) use of surfactants and the addition of non-nutrient facilitating or carriermediated agents.
Humidity and temperature have a direct relationship with absorption of nutrients. As they increase penetration also increases. The total amount of time the nutrient is in contact with the leaf is critical. Optimum pH is a factor that varies from nutrient to nutrient and most good formulators recognize the need to have optimum pH for the nutrient used.
The formulators should also study chemical compounds closely, as many are ineffective as foliar nutrients. For example Shafer and Reed studied a total of 31 organic and inorganic potassium compounds for their efficacy as a foliar fertilizer. Their results showed a broad spectrum in foliar absorption of potassium from both organic and inorganic carriers. Studies from other researchers on many other nutrient compounds show similar results.
Golf course superintendents need to know and trust the expertise of formulators from the various companies who make foliar absorbed nutrients, and follow their commendations.
Modern Foliars
The effectiveness of modern foliar fertilizers nowadays varies significantly. Using both organic and inorganic facilitating agents to transport the cations into and throughout the plants has become a very exact science and is the main difference in the claims between companies in the foliar business. Golf course
superintendents need to separate facts from claims and get a high degree of confidence in the company they choose to work with and to purchase from. The process of building excellent foliar fertilizers is an exacting and complex one.
Many humic and organic materials have the capacity to bind substantial amounts of metals and other cations, and they can therefore exert considerable control over the supply and availability of nutrient elements to plants and in water.
When the metal ion combines with an electron donor, the resulting substance is said to be a complex or coordination compound. If the donor atoms are attached not only to the metal ion but also to each other as well forming a ring, it creates a chelate.
There are good complexes and bad complexes and there are good and bad chelates. Some of the organic agents used in these products are: humic acids from many sources, fulvic acids, ligno sulfates, amino acids, sugars and carbohydrates, hydrolyzed protein mixes and derivatives from the wood pulp industry. Many of these have low stability constants and when mixed with anions such as phosphates may result in precipitation. One again select your
products wisely. When added to the nutrients, organics are biodegradable and available to the plant and the soil micro community as an energy source.
Since the 1950’s synthetic chelating agents have been used as aids in plant nutrition. Among the more popular ones are EDTA, HEDTA and EGTA, and others. They are cost effective and can be effective if used properly but they are generally not biodegradable.
Synthetic chelates are used extensively in many turf products. Many researchers have reported that they may remain as a residue in the plant
tissue or in the soil tying up other nutrients and providing no additional energy source.
Mobility
Absorption is only one aspect of a foliar fertilizer. In addition, the absorbed nutrient generally must be translocated throughout the plant. While absorption is a key process in selecting a foliar applied nutrient, the extent of redistribution or mobility of each nutrient in the plant is an important consideration also.
Buyer Beware
There is little regulation over the complexing and chelate foliar industry.
The presence of an organic or synthetic chelating agent in the formulation legally makes the product a chelate.
It does not matter whether there is enough chelating agent in the mixture to chelate all the metals in the formulation or not to be considered a chelate.
Any agent that can be shown to cause chelation is considered a chelate, without regard to whether it is stable or not.
Unstable chelates that precipitate when mixed with anions, such as phosphorus, are poorly absorbed by the plants and do not translocate well in the plant.
The concentration of these complexing and chelating agents in the various formulations need not be on the label.
I personally believe that the best chelating agents are those that are natural components found in the metabolism of the plant and my personal observation is that they need to compose a high concentration within the formulation.
Summary
I like chelated compounds over non-chelated, complexed products. However, complexed products, in my opinion, are better than those foliars that have neither. There are some good quality chelated liquids out there in the market
place. I like natural organic chelating agents over synthetics. Use the ones that will hold against precipitation with phosphors. Try this easy test: take some water, mix in enough10-34-0 liquid fertilizer to be representative of your
fertilizer mix and add a little of what you are testing and see what happens. If it is a good chelate it will remain in solution while poor chelates will tie up with the phosphorus and cause a precipitate. Many products are not 100% chelated and as I have stated, some companies put only enough chelating agent to
claim its presence. Although classified as a chelate by law it will be ineffective.
Even with organic agents some chelating agents are far superior to others. In most cases, the form of the nutrient will react differently to different agents. Find someone who understands this and uses the form of nutrient and type of chelating agent to give the strongest chelate.
Conclusions
Look at your soil fertilizer program as a “bank”. The soil tests show how much you have on deposit in our “bank” and you balance the nutrients on the cation exchange sites with soilapplied fertilizers. This is traditionally the way golf course superintendents have developed their fertility programs.
Tissue tests are also important and show what our intermittent withdrawals from the soil “bank” are. If we see a need we can make the appropriate “deposit” directly to the plant with foliar nutrients and bypass soil cation exchange and root absorption.
Why foliar feed turfgrasses? Most professionals agree that you can get:
More control with less risk. If you combine soil testing and regular tissue analysis you can tank mix any compatible products in order to give your turf up-to-date needs.
Lower overall nutrient inputs. Since foliar fertilizers are more effective than soil fertilizers you can reduce the overall amount of fertilizer used.
No nutrient leaching past the root zone and therefore no chance of ground water contamination. Since foliar fertilizers are absorbed by the plant and will not leach from the plant they are not present to leach from the soil.
Better response with a poor root system. Because foliar fertilizers are plant absorbed and quickly responsive, you can put nutrients quickly into action even when you have a less than ideal root system.
Better response without optimum soil pH. Foliar fertilizers do not depend on any given soil pH. Foliar Nutrition of Turfgrass
When overseeding, the young plants have a very limited root system and foliar fertilizer is the best way to bring the overseeding into maturity. After maturity, the overseeded cool season turf still has a root system limited to the thatch layer of the bermudagrass. Foliar fertilizers continue to be the best system for nutritional balance.
Good results with plants under stress.
Foliar fertilizers are the very best in a “spoon-feeding program.”
Application needs to be every 7 to 14 days depending on growth, season and how much leaf is removed during mowing.
You can balance these advantages with the following concerns:
All organic and inorganic compounds vary in their efficacy of foliar absorption; therefore choose your formulator wisely.
Absorption is only one aspect of a useful foliar fertilizer. In addition, the absorbed nutrient must be translocated throughout the plant to be effective.
Phytotoxicity can be a concern with some compounds, especially the inorganic compounds.
Foliar nutrition is an effective method of providing a steady flow of nutrients to the turfgrass. In combination with some traditional types of root uptake fertilizers it is another effective management technique for progressive golf course superintendents who wish better control of nutrition and growth.
Gary holds a BS degree in Agriculture and Entomology from Utah State University and a Master of Science degree in Agronomy from Michigan State University. After a 34 year career as a golf course superintendent he retired to become co-founder of Grigg Brother Fertilizers.
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release 1/19/2011 |
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