7 Nutrient Management
Elevated levels of nitrogen (N) and phosphorus (P) have been identified as major contributors to the decline of the health of the Chesapeake Bay and the Delaware Inland Bays. Fertilizers containing N and P are a potential source of nutrients that can be transported in leaching and runoff events. Therefore, ensuring that a nutrient management program emphasizes proper fertilization and maintenance of turfgrass on golf courses reduces the potential for N and P losses to groundwater or surface water. The goal of nutrient management programs is to apply the minimum necessary nutrients and maximize their uptake in order to achieve an acceptable playing surface and to maintain turfgrass density.
7.1 Regulatory Considerations
In Delaware, state laws and regulations apply to N and P applications to turfgrass, including golf courses. The Delaware Legislature passed the Delaware Nutrient Management Act (Title 3 Chapter 22 Nutrient Management) in 1999. The purpose of the Delaware Nutrient Management Law is to:
- Establish a certification program that encourages the implementation of best management practices in the generation, handling, and land application of nutrients.
- Formulate nutrient management programs that maintain agricultural profitability and improve water quality.
- Establish a nutrient management planning program.
- Regulate those activities involving the generation and application of nutrients.
7.1.1 Delaware Nutrient Management Certification
As per the Nutrient Management Certification Regulations, golf courses with 10 or more acres of fertilized land must have an employee certified as a private nutrient handler. Initial certification sessions for turfgrass nutrient management are offered annually (in early winter) by the University of Delaware Cooperative Extension Nutrient Management Program. Initial certification for private nutrient handlers is valid for three years. Certified private nutrient handlers must obtain six continuing education units (CEUs) every three years to maintain their Delaware Nutrient Management Certification. (One CEU = 50 minutes of instruction.)
Large facilities may be able to offer their own training to satisfy the CEU requirement; the University of Delaware Nutrient Management Program should be consulted to be approved for CEU credits. Please note that certification follows the individual and not the facility. If a facility’s certified private nutrient handler leaves, another individual must become certified.
7.1.2 Nutrient Management Planning
All Delaware golf courses with 10 or more acres of fertilized land must have a valid nutrient management plan or a nutrient management general permit.
Nutrient Management Plans
Only a certified nutrient consultant can write a nutrient management plan for a Delaware golf course. DDA maintains a list of public and private consultants who are certified to write nutrient management plans for Delaware operations. Cost-share funds are available through the DDA to offset the costs of obtaining a nutrient management plan. Contact the DDA Nutrient Management Program for more information.
Nutrient management plans are valid for three years. Updates to a nutrient management plan must be completed by a certified nutrient consultant at least every three years, upon significant changes to the operation activities, or when there is an increase in operations of 25% or more. The Delaware Nutrient Management Commission should be informed of plan updates no later than December 15 of the year in which it must be updated.
Nutrients applied to land managed under a nutrient management plan must be handled in accordance with the operation’s approved nutrient management plan and done by or supervised by an individual who is certified by the Delaware Nutrient Management Program. The following standards apply to all nutrient management applications in Delaware:
- Fertilizer applications are prohibited between December 7 and February 15 or to frozen or snow-covered ground.
- Fertilizer applications to impervious surfaces (roads, sidewalks, and other paved surfaces) must be removed on the same day.
- Annual applications of P to soils that exceed 150 UD-FIV (University of Delaware Fertility Index Value = 150 mg/kg Mehlich 3 P) cannot exceed 1 lb P2O5 per 1000 ft2 or a three-year plant removal rate justified by a certified nutrient consultant.
- Soil sampling and testing must be completed every three years.
o Soil test results and nutrient application rate recommendations.
o A copy of the applicable nutrient management plan or nutrient management general permit.
o A log indicating the source (including analyses), rate, dates, and method of application for nutrients (N and P).
- Annual reporting by March 1 every calendar year is required. (DDA provides the form.)
Nutrient Management General Permits
Golf courses may be eligible for a nutrient management general permit, provided they meet the following requirements:
- Land was planted in perennial crops or turfgrass for a minimum of two years.
- A nutrient management plan was implemented for a minimum of three years.
The nutrient management general permit is intended as a substitute for the nutrient management plan specifically for low-risk operations. Golf courses with an approved nutrient management plan in place for a period of three or more years that are interested in applying for coverage under the nutrient management general permit should file a notice of intent (NOI) for coverage with the Delaware Nutrient Management Commission. Upon approval by the Delaware Nutrient Management Commission, golf courses managed under a nutrient management general permit must meet the record keeping and annual report requirements outlined above for the nutrient management plan.
Applications of N and P are managed more strictly under the nutrient management general permit than under a nutrient management plan. Nutrients applied to land managed under a nutrient management general permit must be handled according to the following standards:
- Soil sampling of fertilized areas must be conducted once every three years (at a minimum).
- Fertilizer applications are prohibited within 10 feet of the vegetative edge of any stream, pond, lake, river, drainage conveyance, or stormwater management facility.
- Fertilizer applications are prohibited between December 7 and February 15 or to frozen or snow-covered ground.
- Application of raw animal manure is prohibited.
- Annual applications of P cannot exceed 2 lb P2O5 per 1,000 ft2 (87 pounds per acre) per year unless justified in writing by a certified nutrient consultant.
- Annual applications of P to soils with phosphorus concentrations greater than 150 UD-FIV may not exceed 1 lb P2O5 per 1,000 ft2.
- Single applications of fertilizers containing >70% of N in a water-soluble form should not exceed 1 lb N per 1,000 ft2.
- Single applications of fertilizers that contain at least 30% of the total N in a slow release form (water insoluble N) should not exceed 2 lb N per 1,000 ft2.
- Single applications of soluble N sources should not exceed 1 lb per 1,000 ft2.
- Annual N recommendations presented in Table 3 are acceptable under the general permit with written approval of a certified nutrient consultant.
Annual N applications may not exceed 2 lb N per 1,000 ft2 for standard maintenance and 3 lb N per 1,000 ft2 for high maintenance areas without written approval of a certified nutrient consultant.
Table 3. Annual N regulatory limits for the turf general permit for common turfgrass species grown in Delaware based on maintenance level.
Annual Nitrogen Rate (lb/1000 ft2)
|Standard Maintenance||High Maintenance|
|Fine Fescue (K-31)||2||3-4|
The maintenance level of a turf area is dependent on several factors that demand more nutrients, namely N. High and standard maintenance must be determined by each area and should represent management intensity to include mowing, travel, stress levels, compaction, pest pressure, irrigation, and other management factors, as appropriate.
High maintenance turf includes areas with:
- Frequent mowing (3 or more times per week) to a low height (≤0.75 inches) with removal of grass clippings.
- Irrigated turf.
- Vehicle or personnel traffic that creates visual damage to the turf area.
- Insect pest pressure or disease pressure that demonstrates visual plant damage and stress.
- A sandy growth medium for improved drainage, such as California greens.
Standard maintenance turf includes areas with:
- Limited traffic.
- Grass clippings recycled.
- Native healthy soil structure.
7.2 Soil Testing
Soil testing provides the basis for sound nutrient management and water quality protection programs in golf turf management, especially given the dynamic nature of the sandy soils of many putting greens and tees (Figure 16). In Delaware, golf courses are required to have soils tests at least every three years and maintain records of the results in accordance with the nutrient management plan or general permit. The DDA maintains a list of soil test laboratories. Using the same soil testing laboratory for subsequent soil tests allows for easy comparisons of changes in soil fertility values over time. Keeping soil test results from prior years also allows monitoring changes in soil nutrient levels over time and provides evidence of the impact of nutrient management plans.
A standard soil test provides information on soil pH and the levels of the macronutrients phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) and often contains concentrations of typical micronutrients iron (Fe), zinc (Zn), copper (Cu), or boron (B). Soil test results do not provide soil N concentrations because N constantly fluctuates between plant available and unavailable forms. However, soil test results typically provide a recommendation for N levels and timing of applications. It is important to note that different soil testing laboratories offer different tests as part of their “routine” packages. For example, the University of Delaware Soil Testing Program offers the pH test, the lime requirement test, and the Mehlich 3 soil test for P, K, Ca, Mg, B, Cu, and Mn as part of the routine analysis.
Soil testing labs report extractable macronutrient and micronutrient concentrations using a variety of units, including parts per million (ppm), pounds per acre (lb/A), or as a fertility index value (FIV). The University of Delaware Soil Testing Program uses the Mehlich 3 soil test method for routine fertility testing and reports soil test results for macronutrients as the FIV. Micronutrients (B, Mn, and Zn) and S (as SO42-) are reported in lb/A by the University of Delaware Soil Testing Program. The University of Delaware uses four soil test categories to rate soils in terms of the likelihood of a probable plant response to P, K, Ca, and Mg additions in fertilizers. General interpretations are assigned to each soil test category as follows:
Low (0-25 FIV). The nutrient concentration in the soil is inadequate for the growth of most plants and will very likely limit plant growth. There is a high probability of a favorable response to additions of a nutrient.
Medium (26-50 FIV). The nutrient concentration in the soil may be adequate for plant growth but should be increased into the optimum range to ensure that plant growth is not limited. There is a low to moderate probability of a favorable response to additions of a nutrient.
Optimum (51-100 FIV). The nutrient concentration in the soil is in the range recommended for the growth of all plants. Since there is a very low probability of a favorable response, nutrient additions are rarely recommended.
Excessive (>100 FIV). The nutrient concentration in the soil is above the range recommended for the growth of all plants. Additions of the nutrient are not recommended. Erosion, runoff, and leaching from soils that are excessive in P can have negative effects on water quality.
Soil test reports usually recommend nutrient (including N) and lime application rates, as well as frequency of application. The results form the basis for nutrient management planning for the selection of nutrient sources, rates of application, and appropriate timing to meet site specific needs for greens, tees, fairways, and roughs.
For more information on soil testing, see the following publications:
- Soil Sampling and Analysis, Delaware Nutrient Management Program.
- How to Take a Soil Sample, University of Delaware.
- Recommended Soil Testing Procedures for the Northeastern United States. University of Delaware Extension.
- Interpreting Soil Phosphorus and Potassium Tests, University of Delaware Extension.
7.3 Plant Tissue Analysis
Plant tissue analysis can provide additional information on the nutritional status of a turfgrass stand when used in conjunction with soil testing. While soil test results provide an index of potentially plant available essential nutrients in the soil, they do not indicate how much of any given nutrient that the plant has taken up. Analysis of turfgrass tissue samples indicates the level of macronutrients and micronutrients in the plant. However, low concentrations of a given plant nutrient in tissue may not indicate a lack of nutrient availability but rather of an abiotic problem (such as drought stress or herbicide damage) or a biotic problem (such as an insect or disease issue) that reduces or inhibits nutrient uptake. A lack of regional correlation data and numerous problems regarding taking representative tissue samples further limit the impact of using tissue sampling as the primary tool for adjusting nutrient management programs.
Perhaps the greatest potential use of tissue sampling is for turf grown on soil with a very low cation exchange capacity (CEC), such as the high sand content mixtures used on greens and tees. In these situations, the nutrient retentive capacity of the soil is very low, and the potential for nutrient imbalances (high levels of one nutrient causing excessively low levels of another nutrient) in the plant is thus relatively high. Tissue sampling can indicate when such imbalances are occurring. These situations are most likely to be occur with micronutrients but can also occasionally occur with macronutrients. For more information on collecting plant tissue samples and interpreting the results, see Plant Analysis: An Important Tool in Turf Production.
In Delaware, the DDA Agricultural Compliance Laboratory analyzes samples of fertilizer and agricultural lime sources to ensure that labeling guarantees are met and that the product is safe for the environment. A fertilizer label must contain the following five components:
- guaranteed analysis
- net weight
- name and address of the registrant and licensee
Fertilizers are also often classified as either organic (containing carbon) or inorganic (containing no carbon). Organic fertilizer sources can be a naturally occurring animal or plant byproducts or a synthetic product such as urea or any urea-based compound (ureaformaldehyde, methylene urea, isobutyraldehyde urea, etc.). However, “organic fertilizer programs” are likely using naturally occurring organic sources and not synthetics.
The grade (19-19-19) and the guaranteed analysis are typically most important for fertilizer selection. The grade presents the percentages by weight of N, phosphate (P2O5), and potash (K2O). Note that the grade is not N, P, and K; the percentages of the actual (or elemental) P and K nutrients can be determined by multiplying the P2O5 level by a constant of 0.44 and the K2O level by 0.83. While most soil test recommendations for these nutrients are provided in units of P2O5 and K2O per 1,000 ft2, concentrations are sometimes provided in pounds of the actual nutrient instead. The guaranteed analysis details all nutrients in the product (in addition to N, P2O5, and K2O) on a percent by weight basis.
Complete fertilizers contain N, P2O5, and K2O, while incomplete fertilizers contain only one or two specific nutrient needs (such as 45-0-0, 0-20-0, 0-0-50, 18-46-0). Balanced fertilizers contain equal amounts of N, P2O5, and K2O (e.g., 8-8-8, 10-10-10, or 19-19-19, etc.). Balanced fertilizers are often referred to as “garden fertilizers” because of their use in gardening applications to optimize bloom or fruit yield with phosphate and potassium. The widescale use of balanced fertilizers is often discouraged because of the emphasis placed on applying P only when indicated by a soil test. Unbalanced fertilizers have varying levels of nutrients (such as 29-3-7, common in many turf-specific products).
Nitrogen applications to golf course turf are essential to provide sufficient growth to recover from intense traffic, to minimize the potential for disease incidence, and to maintain sufficient turfgrass density that minimizes weed encroachment, surface water runoff, and soil erosion. Three areas of N applications that are interrelated need to be addressed to develop a sound N management program:
- Source of N in a fertilizer.
- Rates of application (per application and total annual N applied).
- Timing of applications during the year.
A wide range of N-containing fertilizers is available to the turfgrass manager. These fertilizers generally fall into one of two broad categories:
- Fertilizers that contain only soluble, quickly available N.
- Fertilizers that contain some N in a slow release form that is not immediately available for plant use.
7.5.1 Water Soluble Nitrogen
Fertilizers with N that can immediately go into solution, and thus have N that is rapidly available for turf uptake, are categorized as water soluble N fertilizers. These fertilizers, while quickly available for turf use, have the most potential for leaching if used improperly.
The most common water soluble forms used for golf course fertilization contain N in the ammonium form (NH+4). Soluble N fertilizers that contain ammonium N include urea, ammonium sulfate, and ammonium chloride. These fertilizers can produce excellent quality turf without leaching or runoff problems if used properly. The ammonium N can be absorbed by the soil, reducing the potential for N movement. Ammonium sulfate can be particularly useful in suppressing diseases, such as take-all patch in young bentgrass, and other common patch diseases of turfgrass, such as spring dead spot in bermudagrass.
Some water soluble N fertilizers contain N in the nitrate (NO3) form. N leaching and runoff potential is much higher for NO3-N than other forms of N. Thus, where conditions exist that are conducive to leaching or runoff, fertilizers that contain significant amounts of NO3-N should not be used. These conditions include sandy sites (sands and loamy sands) with high water tables, times when turf is not actively growing, and sites that are highly sloped. Fertilizers high in NO3-N include ammonium nitrate, potassium nitrate, and calcium nitrate. Fertilizers that contain predominantly NO3-N should only be used on sites not prone to runoff or leaching, where very rapid response is essential, and on turf that is actively growing. Turfgrass uptake may occur within a few days with NO3-N containing fertilizers compared with seven to 10 days with NH4-N fertilizers. Generally, fertilizers containing significant amounts of NO3-N are not recommended for turfgrass fertilization.
Excessive rates of soluble N per application can result in excessive growth of turf (which can eventually affect tolerance to environmental stress and pest resistance) and can increase the potential for N loss through leaching, particularly on sandy soils.
7.5.2 Enhanced Efficiency Nitrogen
Enhanced efficiency fertilizers allow increased nutrient availability and reduce potential of nutrient losses to the environment (e.g. leaching, runoff, gasesous losses) when compared to an appropriate reference product, such as the soluble fertilizers urea or ammonium sulfate. Enhanced efficiency fertilizers are divided into two groups: stabilized fertilizers and slow-release fertilizers.
Stabilized fertilizers reduce nitrogen loss in its gaseous form via one of two processes – nitrification and ammonia volatilization. Nitrification occurs mostly in areas with high organic matter, high moisture, low oxygen concentrations and slightly acidic to basic soil pHs. Increasing temperatures also increase the rates rate of nitrification. Stabilized fertilizers with nitrification inhibitors reduce the amount of nitrogen converted to nitrate after application.
Ammonia volatilization may occur when ammonium-based fertilizers are applied to calcareous soils but more commonly the transformation of nitrogen to ammonia is accomplished by microorganisms. Factors that affect microbial growth and metabolism of these microorganisms will affect the rate of volatilization. These factors include the amount of urea or ammonium, temperature, pH and moisture affect the rate at which volatilization occur. Increasing temperatures can lead to volatilization. Stabilized fertilizers with chemical additives called urease inhibitors can reduce this volatilization potential and promote nitrogen uptake.
For more information, see the article “Enhanced Efficiency Nitrogen Fertilizers”.
Slow release N fertilizers contain N in a form that delays its availability for plant uptake after application, extending N availability significantly longer than a rapidly available nutrient source such as urea. Slow release N fertilizers include sulfur coated urea (SCU), polymer coated ureas, ureaformaldehyde (UF), methylene ureas, isobutylidene diurea (IBDU), and natural organics.
While varying considerably in individual characteristics and release patterns, slow release N fertilizers typically provide more even turfgrass response and uptake over a longer period of time. The use of slow release fertilizers should particularly be considered on sites that are prone to leaching, as recent studies show that under certain conditions some slow-release nitrogen fertilizers are less likely to leach into groundwater than soluble fertilizers.
Natural organic fertilizers are slow release N fertilizers that are derived from either a plant or animal product and do not contain synthetic materials. They have not been altered from their original state except by physical manipulation (drying, cooking, chopping, grinding, shredding, or pelleting). Most natural organic fertilizers contain P and thus have additional regulations imposed on their application.
7.6 Nitrogen Rates and Timing
7.6.1 Turfgrass Establishment
For establishment of turfgrass on sand-based soils (both natural and modified), the University of Delaware recommends the use of enhanced efficiency fertilizers, preferably products with 50% or more slowly available N sources. Apply 1 lb N per 1000 ft2 at planting using products containing >50% slowly available N to feed the plants for the first four weeks. Warm season grasses should receive additional applications of readily-available N sources at a rate of 0.25 to 0.5 lb N per 1000 ft2 per week for the next four weeks. Fertilize cool-season grasses for the next eight weeks with 0.25 lb N per 1000 ft2 if using fertilizers with <50% slowly available N or 0.5 lb N per 1000 ft2 if using fertilizers with >50% slowly available N.
For establishment of turfgrass on heavier soils (predominantly silt or clay), apply up to 1 lb N per 1000 ft2 of a fertilizer containing >50% slowly available N to feed warm- or cool-season turf for up to four weeks. If readily-available sources of N are used, split the total N application into four weekly applications of 0.25 lb N per 1000 ft2. Follow the initial N application with weekly applications of readily-available N sources at a rate of 0.25 to 0.5 lb per 1000 ft2.
7.6.2 Turfgrass Maintenance
In Delaware, N applications are regulated as part of a nutrient management plan or general permit, as discussed in the Regulatory Considerations section of this chapter. Nitrogen applications must be handled in accordance with the operation’s approved nutrient management plan or in compliance with N rate (Table 3) and timing guidelines of the nutrient management general permit (as applicable). Applications of N fertilizer are prohibited between December 7 and February 15 and to snow-covered or frozen ground outside of this date range for all Delaware golf courses.
7.7 Nitrogen Applications
When possible, maintenance N applications should be split into two or more applications. This strategy meets both turfgrass nutritional needs and minimizes potential water quality concerns. Restricting N application levels is especially important on sand-based putting greens and is easily adapted into green management programs, where it is commonplace for superintendents to “spoonfeed” (0.05 to 0.4 lb N per 1,000 ft2) the turf, making numerous light applications of nutrients on a frequent basis. This strategy balances turfgrass growth and color with requirements for turf health, recovery, and playability, in addition to reducing nutrient leaching potential.
Spoonfeeding can be accomplished with both granular and liquid applications. The practice of liquid feeding or foliar feeding is popular for facilities with spraying equipment. Liquid feeding uses greater than 45 gal/A (1 gal per 1000 ft2) of water, and most nutrient uptake occurs through the root system. Foliar feeding uses less than 45 gal/A water carrier to keep most of the nutrients on the leaf surface for foliar absorption.
Applying fertilizer in water improves the uniformity of distribution and allows small amounts of nutrients to be accurately applied with water as the carrier. Fertigation (delivery through an irrigation system) is another specialized means of delivering nutrients and is especially effective during a grow-in when wet soils are not conducive to spreader and/or sprayer operation. Fertigation performance is only as good as the distribution and uniformity capabilities of the irrigation system. Dispersible granule fertilizer formulations are now available that provide enhanced turf coverage that mimics foliar or liquid feeding. Upon contact with water, a single fertilizer granule separates into several thousand particles, thus coating the turfgrass foliage. This formulation technology is expected to become more widespread.
Phosphorus is a critical nutrient for turfgrass growth and development, playing important roles in energy transformations in plant cells and root development. Phosphorus is particularly critical for new sites being established from seed. On the fertilizer label, the middle number of the analysis represents the percent by weight of P2O5, which can be converted to % P by multiplying by 0.44 (10-10-10 is actually 4.4% by weight P).
In anionic form (HPO42- or H2PO4–), P is highly leachable and is a concern for water quality. However, the complexing of P with other elements (such as aluminum, iron, or calcium) greatly minimizes P leaching in native soils, unless P has been overapplied for many seasons. Phosphates are a potential leaching concern during the grow-in of turfgrasses on sand-based systems that inherently have very low nutrient holding capacity and are subject to frequent irrigation. On sand-based soils, P leaching can also be a concern if over-applied. Therefore, phosphorus should only be applied to established turf when a routine soil test shows need. The application of fertilizers near water resources and/or hardscapes that move stormwater is prohibited under a general nutrient permit.
7.8.1 Phosphorus Rates and Timing
Phosphorus is particularly critical for establishing new stands of turf. Established turf, however, can generally tolerate relatively low levels of soil P. Phosphorus applications are regulated under Delaware law and should be based on results of a soil test. Areas on the golf course that will be fertilized with P must be sampled and tested every three years. Soil testing is recommended on an annual basis for greens and tees, especially in sand-based systems, due to the potential for rapid depletion of soil P due to high maintenance. The University of Delaware’s recommended rates for P applications based on soil tests are shown in Table 4.
Table 4. University of Delaware P application recommendations for golf turf.
|Application Timing and Method||Soil Test Phosphorus Category|
|Pounds P2O5 per 1,000 ft2|
|Broadcast2||2 – 3||1 – 2||0 – 1||0|
|Incorporated3||3 – 4||1 – 2||0 – 0.5||0|
|Maintenance||2 – 3||1 – 2||0 – 0.54||0|
1Facilities managed under a Delaware Nutrient Management General Permit are prohibited from applying P at a rate >2 lb P2O5 per 1000 ft2. Higher rates are restricted to those facilities managed under a nutrient management plan with written justification by a certified nutrient consultant.
2Surface broadcast or incorporated into soil to a depth <2 inches.
3Incorporated into soil to a depth >2 inches depth.
4Maintenance applications of P to soils testing in the high category are recommended only to encourage recovery in situations where turfgrass has been severely damaged.
7.8.2 Phosphorus Applications
For facilities managed under a nutrient management general permit, annual applications of P to established turf cannot exceed 2 lb P2O5 per 1,000 ft2 (87 pounds per acre) per year unless justified in writing by a certified nutrient consultant. Annual applications of P to soils with phosphorus concentrations greater than 150 UD-FIV may not exceed 1 lb P2O5 per 1,000 ft2. For golf courses under a nutrient management plan, annual applications of P to established turf growing soils that exceed 150 UD-FIV cannot exceed 1 lb P2O5 per 1000 ft2 or a three-year plant removal rate justified by a certified nutrient consultant. However, researchers have shown little benefit to applications of P to soils where soil test P concentrations are above the agronomic optimum, even for overseeding, spot renovations, or sodding.
Applications of P fertilizer are prohibited between December 7 and February 15 and to snow-covered or frozen ground outside of this date range for all Delaware golf courses.
Potassium is not a direct component of any organic compound within a plant but is heavily involved in many biochemical responses. K is the nutrient that most impacts water relations within the plant, sometimes referred to as the “antifreeze” and “coolant” nutrient of the plant world. Potassium is generally more critical for established turf and may play a role in drought, heat, cold, and wear tolerance. Potassium is not considered to be an environmental concern that negatively impacts water quality and therefore does not receive the regulatory attention that N and P do.
The University of Delaware provides K recommendations for establishment and maintenance. However, K applications are generally more critical for established turf. While soil tests should be taken routinely to monitor soil K levels, experience has shown that K fertilizer rates that are approximately half that of the annual N fertilizer rate are generally sufficient to maintain adequate soil K levels. Recommended rates for soil test-based K applications are shown in Table 5.
Table 5. University of Delaware K application recommendations for golf turf.
|Application Timing and Method||Soil Test Potassium Category|
|Low (0-25 FIV)||Medium (26-50 FIV)||High (51-100 FIV)||Excessive (>100 FIV)|
|lb K2O per 1,000 ft2|
|Broadcast1||2 – 3||1 – 2||0 – 2||0|
|Incorporated2||3 – 5||1 – 2||0 – 2||0|
|Broadcast||2 – 4||1 – 3||0 – 2||0|
1Surface broadcast or incorporated into soil to a depth <2 inches.
2Incorporated into soil to a depth >2 inches depth.
7.10 Secondary Macronutrients
Secondary macronutrients are essential to plant function and are required in quantities less than N, P, and K, but more than micronutrients. These include Ca, Mg, and S. Each are described briefly below:
- Calcium: Primarily a component of cell walls and structure. Found in gypsum, limestone, and calcium chloride.
- Magnesium: Central ion in the chlorophyll molecule and chlorophyll synthesis. Found in S-Po-Mg, dolomitic limestone, and magnesium sulfate.
- Sulfur: Metabolized into the amino acid cysteine, which is used in various proteins and enzymes. Found in ammonium sulfate, elemental sulfur, gypsum, and potassium sulfate.
Understanding the role of each micronutrient within the plant should provide a greater understanding of the key role these nutrients play in proper turfgrass management. Micronutrients are just as essential for proper turfgrass health as macronutrients but are required in very small quantities compared with macronutrients. Micronutrients include FE, Mn, B, Cu, Zn, Mo and Cl.
- Iron: Part of the catalytic enzymes, Fe is required for chlorophyll synthesis affecting photosynthesis, nitrogen fixation, and respiration. Delaware soils contain a fair amount of Fe. However, because it complexes with other nutrients in the soil, Fe is the micronutrient most likely to be deficient. Iron occurs primarily as oxides and hydroxides that are sparingly soluble in well-aerated soils above pH 4.0. Root exudates of organic acids from deeply rooted plants are generally able to solubilize sufficient iron to optimize plant growth, but high N rates and close mowing decrease root growth relative to shoot growth and limit uptake capability. The inherently low levels of Fe in high-sand putting green soils, and some of the native sandy sands, along with the relatively high supply of N and P in these management systems can further complicate Fe uptake.
- Manganese: Involved in photosynthesis, Mn is required as a cofactor for about 35 enzymes. Lignin biosynthesis depends on Mn.
- Boron: Found in the cell wall. B is probably required for the structural integrity of the cell wall.
- Copper: Cu-protein plastocyanin is involved in photosynthesis and is a cofactor for a variety of oxidative enzymes.
- Zinc: Zn is a structural component of enzymes and is required for protein synthesis. Carbohydrate metabolism is affected by Zn.
- Molybdenum: Mo is primarily related to nitrogen metabolism and is involved in the structural and catalytical functions of enzymes.
- Chlorine: Cl is required for the oxygen-evolving reactions of photosynthesis and appears to be required for cell division in both leaves and shoots.
To correct Fe deficiency, apply ferrous sulfate or iron chelate at a rate of 0.5 ounces Fe per 1,000 ft2. Iron applications should be avoided during the heat of the day. Applications can be made three to four times in summer and/or fall. Repeated applications may be needed to prevent reoccurrence of Fe deficiencies. Foliar applications of Fe are not recommended between March and June. Granular Fe applications generally do not provide as rapid color responses as foliar applications due to the rapid complexing of the Fe in the soil. As such, soil applications of granular materials are not recommended.
Deficiencies of other micronutrients are rare except on mostly sand soils. Again, maintaining appropriate soil pH ensures satisfactory availability and prevents potential phytotoxicity issues. Some notable Zn and Mn toxicity issues on golf greens have occurred over the years where a popular fungicide (mancozeb) has been repeatedly applied for disease and algae suppression. Zn and Mn solubility can become so high at low soil pH relative to other nutrients that turf phytotoxicity occurs. Maintaining the pH at an appropriate level by application of a soil test-recommended lime application is the easiest way to manage this problem. Where supplemental micronutrient applications are needed (most often indicated by tissue testing), chelated micronutrient formulations are very effective.
7.12 Soil pH
Maintaining soil pH in an optimum range is important for maximizing the efficiency of nutrient use and can be important in reducing weed and disease problems. Turfgrass can withstand a rather broad range of soil pH, but 6.5 is generally considered the target pH for golf turf in Delaware. Wide deviations from this target pH can result in reduced P and micronutrient availability and can interfere with soil N metabolism and availability. Depending on turfgrass species, problems may start to occur when soil pH is below 5.4 or above 7.8. Soil testing for pH is recommended to maximize efficiency of nutrient availability.
Most of the native soils of Delaware are slightly to moderately acidic. The use of acid-forming fertilizers can further decrease soil pH. Therefore, Delaware soils typically require periodic liming to make the rooting environment hospitable for root exploration and development.
Golf turf soils are rarely too alkaline in the Mid-Atlantic. If soil pH is too high, nutrient deficiencies and toxicities are just as prevalent as for low pH soils. High alkalinity is typically due to excessive lime applications made without soil test recommendations. This situation should be avoided due to the difficulty of managing high pH soils as compared with low pH soils.
7.12.1 Liming Rates
The University of Delaware makes recommendations for limestone applications to achieve a soil pH of 6.5 based on the results of a routine soil test (which includes the soil pH and lime requirement tests). Lime recommendations are based on the use of pure CaCO3, use Calcium Carbonate Equivalence (CCE) values to calculate an equivalent rate of liming material if calcific lime is not used as the liming material. See the fact sheet Liming Materials for more information on calculating CCE values.
Whenever possible, soil pH should be adjusted prior to establishment as pre-plant incorporation greatly accelerates the neutralization of the acidity throughout the root zone. In addition, applying limestone approximately one month or more before seeding can minimize potential P availability problems and the potential for volatilization loss of applied N. When liming established turf, no more than 50 pounds of lime per 1,000 ft2 is recommended in a single application and 25 pounds per 1,000 ft2 application to golf putting greens. If recommended rates exceed these thresholds, then the total amount of lime should be split into two or three treatments that are applied two to four months apart until the whole amount of lime is applied.
The beneficial effects of liming occur only where lime and soil are in contact. Traditional liming materials applied to mature turf stands are sparingly soluble and react strongly with the soils that they contact. As a result, most lime materials are relatively immobile in the soil and surface applications generally affect no more than the surface two to three inches during a growing season. To move more lime into the soil profile, lime can be applied in conjunction with hollow-tine core aerification events. Lime is typically applied during the active growing season when the turf can quickly rebound from the damage/surface disruption of the coring. Applying lime in the fall and winter months is also possible because the foliar burn (leaf desiccation) potential from the liming material is very low, and the freezing and thawing of the soil over winter can aid in mixing lime throughout the root zone.
While these recommendations should result in satisfactory establishment in most situations, many factors can impact whether modifications of these recommendations are warranted for a specific site. For example, it may be desirable to maintain a lower soil pH (5.4 to 5.7) if diseases such as take-all patch of bentgrass, summer patch of Kentucky bluegrass, or spring dead spot of bermudagrass are of concern.
7.12.2 Soil Acidification
Turfgrass areas with excessively high pH can be amended gradually over time through the application of acid- forming N fertilizers such as ammonium sulfate. Where pH is so high it requires immediate attention, the chemical amendments of choice are elemental sulfur or aluminum sulfate. Depending on the source used, maximum application levels are quite restricted due to the caustic nature of these materials (no more than 5 lbs per 1,000 ft2 in a single application). Like liming recommendations, adjustments to lower soil pH should only be based on a soil test.
7.13 Fertilizer Equipment Selection and Maintenance
Different types of spreaders are available, and advantages and disadvantages exist for each. In addition, not all fertilizers can be spread with every spreader. For example, a drop spreader can damage the sulfur coating in sulfur-coated urea, essentially leading to an increase of soluble urea. It is important that you use the appropriate type of applicator or spreader for the fertilizer.
Most importantly, accurately calibrated sprayers or spreaders are essential for proper application of fertilizers. Incorrectly calibrated equipment can easily apply too little or too much fertilizer, resulting in damaged turf, excess cost, and greater potential of nutrient movement off-site. An excellent resource for spreader care and calibration can be found at Penn State’s Department of Plant Science. Spreaders should also be thoroughly cleaned after use due to the high salt content that corrodes metal parts and in keeping with the BMPs for equipment washing as discussed in the “Maintenance Operations” chapter of this document.
7.14 Nutrient Management Best Management Practices
Nutrient Management Planning Best Management Practices
- Follow the nutrient management plan or general nutrient management plan fertilizer application rates.
Soil Testing Best Management Practices
- Divide the course into logical components such as greens, fairways, tees, and roughs. In addition, do not combine samples from areas that have different past management histories, exhibit different problems, or have different turfgrass species.
- Ten to 15 soil samples should be randomly taken from each sample area and blended together to provide a representative, uniform soil sample.
- Each soil sample should be taken from the same depth, with thatch removed.
- Use the same soil testing laboratory for subsequent soil tests to compare changes in soil fertility values over time.
Fertilizer Applications Best Management Practices
- Licensed nutrient applicators should apply nutrients or directly supervise nutrient applications by experienced or trained staff.
- Prevent fertilizers from being deposited onto impervious surfaces.
- Avoid applying fertilizer to soil at or near field capacity or following rain events that leave the soil wet.
- Do not apply fertilizer when heavy rains are likely.
- Maintain buffer areas around waterbodies that are not fertilized.
- Choose the appropriate type of spreader for a given fertilizer.
- Identify those areas on the golf course most prone to potential losses or potential impacts on water quality.
- On highly sloped areas, use slow release N sources and apply a maximum of 0.9 pounds N per 1,000 ft2 per application and avoid application prior to any expected high rainfall. If suitable for the site, use species such as hard or chewings fescue or other species with lower N requirements.
- Use species with low N requirements in areas immediately adjacent to water.
- On sandy soils in areas with high water tables, use slow release N sources or spoon feed to apply at a maximum rate of 0.9 pounds N per 1,000 ft2.
- Apply slow release N fertilizers at the appropriate time of year to maximize release characteristics. For example, an application of slow release N to warm-season turfgrass in fall may not be as effective as the same application applied in early summer because of the prolonged release time in fall.
- Do not use fertilizers that contain significant amounts of NO3-N on sites conducive to leaching and runoff, such as sandy sites (sands and loamy sands) with high water tables and highly sloped sites or when turf is not actively growing.
- Irrigate turf after it has been fertilized to bring fertilizer into contact with soil and to move soluble N into the soil. Irrigation intensity must be low enough so that water infiltrates soil instead of contributing to runoff.
- When feasible, leave clippings. This may reduce annual fertilizer N requirements.
- Direct drainage systems from greens, tees, and fairways to areas of lower maintenance, such as non-irrigated roughs.
- Appropriate organic matter should be part of the root zone mixture for putting green construction to increase nutrient retention. (See USGA specifications.)
- Avoid applying fertilizer to soils that are at, or near, field capacity or following rain events that leave the soils wet.
- Do not apply fertilizers within 15 feet of waterways; or within 10 feet if a drop spreader, rotary spreader with deflector, or targeted spray liquid is used.
Soil pH Best Management Practices
- Test soil pH as part of soil testing.
- Adjust soil pH as needed, targeting 6.5 as an ideal pH for Delaware soils.
Fertilizer Equipment Best Management Practices
- Accurately calibrate sprayers or spreaders.
- Thoroughly clean equipment after and in keeping with the BMPs for equipment washing.
- Perform routine maintenance on equipment, such as inspecting hoses, maintaining tire pressure, changing oil, cleaning filters, and replacing old nozzles.