7 - Nutrient Management
Proper fertilization and nutrient management are a key cultural practice that supplies essential nutrients to turfgrass plants. A sound fertilization program utilizes information from soil and tissue analysis in order to ensure turfgrass health, performance, and recovery. Proper fertilization in combination with other culture practices allow for sustainable turfgrass while reducing other chemical inputs.
Regulatory Considerations
Local and state regulations are in place to better manage nutrient risks based on the unique conditions that exist by location. Designing a nutrient management plan within these regulations addresses local concerns minimizes risks to each unique ecosystem.
Depending on the location, regulatory agencies may include federal, state, or local policies.
In Connecticut, there are varied terrain and considerations. All BMP policies should be tailored to local regulations.
The goal of a proper nutrient management program should be to apply minimal nutrients to achieve an acceptable playing surface in the most efficient manner helping the plant to recover from the many stresses that it faces.
Overview
There are at least 17 nutrients essential for turfgrass growth.
These nutrients are separated into 2 categories, macronutrients & micronutrients.
Macronutrients are such as Nitrogen, Carbon, Oxygen, Phosphorous, Potassium, Calcium, Magnesium, & Sulfur are required in relatively large amount.
Micronutrients such as Iron, Manganese, Zinc, Boron, Molybdenum, Copper, Chlorine, & Nickel are usually required in lower amounts.
Turfgrasses obtain Oxygen, Hydrogen, & Carbon from the atmosphere and water, the remainder are obtained primarily through roots in the soil. (Some may be obtained by foliar applications).
Soil testing is an important component in deciding what nutrients and in what quantities that each nutrient is required for plant health.
Factors affecting fertilizer application decisions include plant species, soil pH, & site conditions.
Reference the New England Regional Nitrogen and Phosphorus Fertilizer and Associated Management Practice Recommendations for additional BMPs: https://extension.unh.edu/resources/files/Resource002468_Rep11092.pdf
Best Management Practices
Apply nutrients when turfgrass is actively growing
Apply N rates and intervals to maintain moderate growth and recuperative potential
Use light, frequent applications (spoon feeding) to provide consistent nutrition and minimize potential for leaching and runoff.
Apply slow-release N fertilizer at the appropriate time of year to maximize the products release characteristics.
Select a N:K fertility ration based on turf use, rootzone, and clippings management
Exercise caution when applying nutrient applications during turfgrass establishment as these applications are particularly susceptible to loss via leaching and runoff.
Provide appropriate rates and products to minimize N loss without reducing turfgrass establishment.
Be aware of different spreaders and understand the advantages and disadvantages of each.
Calibrate spreaders regularly to reduce environmental risk and increase efficiency.
Reduce environmental risk by properly storing and loading fertilizer and cleaning up any spills.
Avoid applying fertilizers to soils that are at, or near, field capacity or following rain events that leave the soils wet.
Do not apply fertilizer when the National Weather Service has issued a flood watch, tropical storm or hurricane watch or warning or if heavy rains are likely.
Soil Testing
The purpose of soil testing is to provide a detailed report which includes measurable variables including pH, soil organic matter, soil salts, and nutrients available for plant use. It also offers a prediction of a plants response to applied nutrients. Proper use of testing results includes analysis, interpretation, and recommendations. Through these and record keeping, decisions can be made to apply those nutrients that are deficient and need to be applied for turf health and sustainability.
Best Management Practices
Accurate and consistent sampling is essential to providing useful information over any period of time.
Divide course into measurable components such as greens, fairways, tees, etc. for each hole or area to be tested.
Take 10-15 samples from each area and blend together to get a uniform and representative mixture.
Each soil sample should be taken at an equal depth.
The purpose of a soil test is to provide the grower with a prediction of a plant’s response to an applied nutrient.
If the location has correlation data between a given nutrient applied to a soil and a response to that nutrient by turfgrass, then recommendations may provide expected results.
If the location does not have correlation data, then soil test recommendations may be of little value.
Use an extraction method appropriate for the soil and remain consistent in using this method when comparing test results from different periods of time.
Keeping soil tests from previous years will allow you to observe changes over time and make appropriate decisions in the future.
Plant Tissue Analysis
Plant tissue analysis is a valuable tool for guiding fertilizer recommendations. With tissue analysis, the clippings are analyzed for nutrient concentration that is actually in the plant. These values are compared to a critical level range indicating deficiency, sufficiency, or excess. Some believe this method is more accurate since it measures the actual concentrations of nutrients actually taken up by the plant. Some of the shortfalls of this method are cost, testing availability, and speed of results. When using tissue analysis, it is recommended that the following should be monitored. Turfgrass quality, clipping yield, and performance. By recording and analyzing these variables, future nutrient management can be established.
Best Management Practices
Tissue samples may be collected during regular mowing.
Do not collect tissue after any event that may alter nutrient analysis.
Place tissue in paper bags. Do not use plastic.
If possible, allow tissue samples to air dry before mailing them.
Poor quality turfgrass that is of concern should be sampled separately from higher quality turfgrass.
When turfgrass begins to show signs of nutrient stress, a sample should be collected immediately.
More frequent tissue sampling allows more accurate assessment of turfgrass nutrient status and how it changes over time.
The quantity of tissue analysis should be based on individual site needs. Two to four site tests per year are common on greens while one to 2 tests per year are common on fairways and tees.
Keeping tissue tests from previous years will allow you to observe changes over time.
Tissue testing can provide good evidence of the impact of nutrient management programs.
Fertilizers Used in Golf Course Management
An understanding of the components of fertilizers, the fertilizer label, and the function of each element within the plant are all essential in the development of an efficient nutrient management program.
Macronutrients
Macronutrients are required in greater quantities and include Nitrogen(N), Phosphorous(P), & Potassium(K). Understanding the role of each of these macronutrients within the plant will provide you with a greater understanding of why these nutrients play such a key role in proper turf management.
The Role of Nitrogen
Nitrogen is typically required in greater quantities by turfgrasses than any other element except carbon(C), hydrogen(H), and oxygen(O). Nitrogen plays an important role in numerous plant functions including being an essential component of amino acids, proteins, and nucleic acids.
The goal of all applied nutrients is to maximize plant uptake while minimizing nutrient losses. Understanding each process will increase ability to make sound management decisions and increase profitability while reducing environmental risk.
To aid in this, you must understand the fate and transformation of nitrogen(N) along with the release mechanisms and factors affecting N release from various N sources.
Understanding how certain N sources should be blended and applied is an essential component in an efficient nutrient management plan. In many cases, N sources are applied without regard to how they are released. Each N source is unique and should be managed accordingly. Applying a polymer coated urea in the same manner as a sulfur coated urea greatly reduces the value of the polymer coated urea. Similarly, applying a 2 lb rate of N from an ammonium sulfate may cause burning but on the other hand, applying a 2 lb rate of a polymer coated urea may not yield the quick response of an ammonium sulfate urea. Rate, application date, location, and turfgrass species should all be considered in the nutrient application decision.
Soluble nitrogen sources:
Urea (46-0-0)
Ammonium sulfate (21-0-0)
Diammonium phosphate (18-46-0)
Monoammonium phosphate (11-52-0)
Calcium nitrate (15.5-0-0)
Potassium nitrate (13-0-44)
Fast release sources of nitrogen(N) are often characterized by short bursts of growth followed by slow growth resulting in a peak and valley growth response by turfgrasses that may result in compromised root growth.
Slow-release nitrogen sources:
Sulfur coated urea
Polymer/resin coated
Isobutylidene diurea
Urea-formaldehyde reaction products
Natural organic
Slow release fertilizers are any fertilizer where the release of the N into the soil is delayed either by requiring microbial degradation of the N source, by coating the N substrate which delays dissolution of N, or by reducing the water solubility of the N source.
Some fertilizers combine both slow and fast release forms combining the advantages of both.
Urease and nitrification inhibitors:
Urease inhibitors reduce the activity of the urease enzyme resulting in a reduction of volatilization and increase in plant available N.
Nitrification inhibitors reduce the activity of Nitrosomonas bacteria, which are responsible for the conversion of NH4 to NO2. This reduced activity results in a reduction of N loss via denitrification and an increase in plant available N.
Role of Phosphorous (P)
Phosphorous can be a growth limiting factor for many organisms and is a major contributor to eutrophication of water bodies. Proper timing and rates should be adhered to in order to reduce the risk of off-site movement.
Phosphorous forms high-energy compounds that are used to transfer energy within the plant. Phosphorous may remain in an organic form or may become incorporated into organic compounds and application rates should be based upon soil test results from documented correlations demonstrating a turf response to soil test phosphorous levels.
The role of phosphorous in turfgrass culture is important in seed germination, seedling vigor, & rooting responses. Therefore, phosphorus is critical in turfgrass establishment and should be incorporated during establishment when soil tests indicate a deficiency.
P deficiency symptoms:
Initially, reduced shoot growth and dark green color may be observed
Later, lower leaves may turn reddish at the tips and then the color may progress down the blades.
P fertilizer sources:
Diammonium phosphate
Concentrated superphosphate
Monoammonium phosphate
Natural organics
Role of Potassium (K)
Potassium is of no environmental concern, but can be an economic concern, especially when potassium is over utilized, which is quite common. As a general rule, concentrations of potassium are about 1/3 to ½ of Nitrogen.
Potassium is not a component of any organic compound and moves readily within the plant. Potassium is a key driver of osmoregulation which has been documented to increase stress tolerance.
K deficiency symptoms:
Except under severe, documented deficiencies, K may not have an observable influence on turfgrass appearance. Yellowing of older leaves followed by tip dieback and scorching of leaf margins have been reported.
Tissue concentrations of less than 1% are considered deficient.
K sufficiency ranges:
Consult UConn/UConn CAHNR for sufficiency ranges for the specific location
K fertilizer sources:
Potassium sulfate
Potassium chloride
Potassium nitrate
Secondary Macronutrients
Secondary macronutrients are essential to plant function and are required in amounts less than N, P, & K but more than micronutrients. These include calcium (Ca), magnesium (Mg), & sulfur(S).
Micronutrients
Understanding the role of micronutrients within the plant should provide you greater understanding of why these nutrients play such a key role in proper turfgrass management.
Micronutrients are just as essential as macronutrients, but they are required in very small quantities compared to macronutrients. Micronutrients include iron (Fe), manganese (Mn), boron(B), copper (Cu), Zinc (Zn), molybdenum (Mo), and Chlorine (Cl).
Consult UConn/UConn CAHNR for sufficiency ranges of micronutrients in the specific location.
Best Management Practices
Maintain a pH near 6.8 to optimize nutrient availability and reduce fertilizer requirements
To increase soil pH, apply a liming material (calcium carbonate, calcium oxide, dolomitic limestone) that contains Ca or Ca/Mg and neutralizes acidity.
To lower soil pH, products containing Sulfur(S) should be applied.
In some cases, utilizing injection pumps into irrigation water to address pH can be beneficial.
Soil pH
Identifying and maintaining soil pH plays an important role in turfgrass growth. Nutrient availability along with flora and fauna activities are closely associated with the pH of the soil. Soil pH is the result of chemical reactions that take place in the soil and affect the degree of acidity or alkalinity of a soil solution.
Soil pH in Connecticut may vary but most turfgrass soils are in the range of 5.0 to 7.0. The soil pH is usually a function of precipitation in a region which induces more leaching of Ca, Mg, & K ions which are replaced with H & Al ions. Connecticut soils tend to be more acidic. Other factors that affect soil pH are parent material of the soil, organic matter content of the soil, and fertilizing practices. Nitrogen applications generally have an acidifying affect because of the release of H ions.
In general, most turfgrasses can tolerate a wide range of soil pH’s, but it is recommended that Connecticut soils have a pH of 6.0 to 7.0. Kentucky bluegrass does best with a pH between 6.5-7.0 while ryegrass and bentgrass can tolerate a slightly lower pH.
At extreme pH values, certain essential nutrients become less available, while others become more available leading to excessive availability. At highly acidic levels of pH, there is a decrease in microbial activity which can lead to decreased mineralization and decomposition of organic matter causing potential loss of favorable soil structure, and excessive thatch buildup.
Correcting Acidic Soils
When soil test shows an acidic soil, the following materials are most common:
Calcitic limestone- CaCo3
Dolomitic limestone- CaMg (CO3)
Soil tests are the only way to determine if the turf soil requires lime. The rate required for liming materials is partly determined by soil texture. Soils with more clay and silt require more lime than sandier soils. Soils with higher organic matter content may also require more lime than a soil with a lower organic matter content.
It is recommended that since most Connecticut soils are sandier, a maximum rate of 50#/1000 square feet be applied at any one time on established turfgrass stands. If soil tests call for more lime, then split applications should be utilized with a few months’ interval in between. When establishing new turf, the total limestone requirement may be incorporated into the top 4”-6” of soil before seeding.
Lime moves slowly through the soil profile at a rate of .5”-1” per year. Therefore, it may take 2 or more years for the lime to increase the pH of the rootzone. It is important to not allow the pH to drop too low before applying corrective measures. It is recommended to test soil every 2 years to determine pH and make corrective applications. Fall applications are best as are applications during aeration to move lime more quickly into the rootzone.
Correcting Soil Alkalinity
If a soil test shows a pH of above 8.0, then it must be lowered. In this situation, an application of Sulfur(S) at a rate 3#-5#/ 1000 square feet to decrease pH to more favorable levels. Sulfur can be applied by using elemental Sulfur, Ammonium sulfate, iron sulfate, or potassium sulfate.
