6 Nutrient Management

All plants require nutrients to sustain growth and development. Certain essential nutrients are classified as either macro- or micronutrients, based on the amount needed by plants rather than their importance for plant growth. Macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), and magnesium (Mg). Micronutrients include iron, zinc, copper, chlorine, nickel, molybdenum, boron, and manganese. Micronutrients are required in significantly lower amounts than macronutrients. However, a deficiency or excess of these micronutrients can have a profound influence on plant growth.

Proper nutrient management usually includes the following steps:

• Determine plant needs (such as light levels, traffic levels, irrigated or not, and expected visual quality).
• Assess the soil reservoir for availability (soil testing).
• Determine nutrient needs and select the proper source of nutrient fertilizer (most are combination products).
• Decide the rate, timing, and frequency of application.

Golf course managers must ensure that all supplemental fertilizer is handled and applied to maximize plant response and minimize off-site movement. N and P re the most important macronutrients to manage correctly because they are critical to both plant health and water quality.

6.1 Regulatory Considerations

The NYS Nutrient Runoff Law (New York State Environmental Conservation Law, article 17, title 21 and Agriculture and Markets Law § 146-g) prohibits and restricts the use of lawn fertilizers as follows:

• Phosphorus-containing fertilizers with a phosphate (P2O5) content greater than 0.67% cannot be used unless soil tests show a phosphorus deficiency or the fertilizer is being used to establish new seeded or sodded turf.
• No lawn fertilizers can be applied between December 1 – April 1.
• If any fertilizer is applied on sidewalks, driveways or other impervious surfaces, it must be swept up to prevent it from washing into drains or waterways. It cannot be hosed off.
• No fertilizer can be applied within 20 feet of any water body unless:
  • There is at least a 10-foot buffer of shrubs, trees or other plants between the area fertilized and the water.
    OR
  • The fertilizer is applied using a spreader guard, deflector shield or drop spreader and applied no closer than 3 feet from water.

Localities may have additional fertilizer use restrictions; for example, Suffolk and Nassau counties have their own fertilizer laws to restrict nitrogen from fertilizer from reaching waterbodies.

6.2 Nutrient Availability and Soil pH

The pH of a soil influences the entire soil chemical environment and fundamentally determines nutrient availability, fertilizer response, and soil biology. In general, a neutral pH is considered adequate for most turfgrass needs; however, slightly more acidic pH can allow for increased levels of metal ions to become soluble and is often favored as a means of increasing the competitiveness of creeping bentgrass and fine fescue over annual bluegrass. More information on soil pH can be found on the Nutrient Availability and pH web page on the NYS BMP website.

6.3 Soil Testing

Soil testing is the beginning of precise nutrient management programs for all nutrients other than nitrogen. Soil testing can be used to determine nutrient levels, make fertilizer recommendations, and in some cases diagnose the cause of poor performing turf. Assessing the existing reservoir of available nutrients in the soil can minimize the need for supplemental applications of fertilizer, which saves money while protecting the environment.

Soil nutrient analysis aids in determining whether nutrient deficiencies exist, as many soils have various levels of nutrient holding capacity, often referred to as cation exchange capacity (CEC). For example, sand-based systems, which have only a limited amount of stored minerals, may demand more mineral additions. Determining supplemental nitrogen needs is typically not based on soil tests as the method of extracting N and the subsequent calibration with plant growth have not been established.

Information on soil sampling, laboratory analysis, interpreting test results, and supplemental plant analysis can be found on the Soil Testing web page on the NYS BMP website.

6.4 Nutrient Management Planning

Fertilizer programs are ultimately designed to supply nutrients to the turf as they become unavailable over time. The goal of a successful nutrient management program should be to sustain even levels of plant available nutrients for a uniform growth rate and to sustain adequate recuperative potential to meet expectations of quality and turf performance, while minimizing excessive growth and the risk of nutrient loss to the environment. One approach to achieving these goals is to utilize the Minimum Level for Sustainable Nutrition (MLSN) Guidelines, developed by PACE Turf.

6.4.1 Nitrogen Fertilization

Using the right product at the right time and at measured rates of application maximizes plant use of the fertilizer and minimizes the risk of nutrient leaching or runoff. However, determining these best practices requires an understanding of other important factors, such as soil issues, plant issues, product characteristics, and application considerations.

Readily available N sources, such as water soluble N (WSN), provide rapid turfgrass growth and color responses, but are more prone to leaching, particularly in sand-based soils. Slow release N sources are more variable in N content and release characteristics. Most N sources can be applied in granular or liquid form. N fertilizer sources are discussed in detail on the Nitrogen Fertilizer Use web page on the NYS BMP website.

Soil Issues

• Soil Type: Well-drained soils with coarse textures and high percolation rates have lower water holding capacity, greater infiltration, and higher risks of leaching.
• Organic Matter: Soils with low amounts of organic matter have lower biological capacity to assimilate nitrogen and are more susceptible to leaching.

Plant Issues

• Growth Phase: Newly seeded areas pose higher risks of leaching and runoff than well-established stands of turfgrass. Once established, the increased density of root mass increases nitrogen uptake while reducing the risk of leaching. Turfgrass in early stages of growth (1 to 20 years or more, depending on the organic matter starting point) has increasingly greater capacity to store and release nitrogen, reducing fertilizer requirements. The lower the amount of organic matter present in turfgrass, the longer the period of storage will be. As the site matures and the amount of organic matter accumulates (20 to 50 years), it poses a higher risk of leaching than younger turf.

Product Characteristics and Application

• Product: The best strategy for use of water soluble fertilizers is light rates of 0.5 lbs N/1,000 sq. ft in general; 0.4 lbs N/1,000 sq. ft on sand; and no more than 0.7 lbs N/1,000 sq. ft on other soils (assuming no heavy rain events) and more frequent applications. This practice more closely matches plant uptake and ensures minimal leaching past the turf root zone.Water insoluble or slow release products, including organics or stabilized products, used properly, have a lower risk of impairing water quality through leaching and runoff. Release rates of combined fertilizer sources and applications can increase or “stack” the amount of available nitrogen. The combined total nitrogen can possibly leach nitrogen even if individual products would not.
• Fertilizer Rate: Excessive applications of any nitrogen-based fertilizer product can create high soil nitrate levels (>1.0 ppm) susceptible to leaching.
• Timing: Application of any nutrient to saturated soil or prior to heavy rainfall can lead to significant off-site movement. Applications made too early in the spring or too late in the fall result in higher soil nitrate levels, posing a greater risk to groundwater quality. Similarly, applications should be reduced during summer decline when plant uptake decreases. Research has not shown an appreciable difference in turf quality using different schedules of application. Applications made every month compared with split schedules of spring and fall, spring only or fall only show reasonable consistency. Light and frequent applications may provide the most consistent quality and limit the susceptibility of losses to leaching and runoff. Low rates of N associated with light and frequent applications may require that applications be made using spray equipment to uniform coverage and response.

6.4.2 Phosphorus Fertilization

As with nitrogen, using the right phosphorus product at the right time and at measured rates of application maximizes plant use of the fertilizer and minimizes the risk of leaching or runoff. This requires considerations of soil and plant issues, as well as other sources of phosphorus that may need to be considered. Phosphorus can be supplied by a number of sources in fertilizers, biosolids, or as an integral by-product of other soil amendments, natural organic fertilizers, or bio-stimulants. These are discussed in detail on the Phosphorus Fertilizer Use web page of the NYS BMP website.

Soil Issues

• Phosphorus fixation increases with increasing clay content in the soil. The larger amount of surface area associated with clayey soils and the aluminium-iron minerals in the lattice help adsorb more P than other soils. In calcareous soils, the adsorption is associated with calcium carbonate (CaCO₃).
• Larger fertilizer additions are required to maintain a level of plant available P in finer soils compared with that in coarser, sandy soils. The risk of leaching P is highest in sandy soils.
• The rate of biological activity, and therefore P mineralization, increases with increasing temperatures. Fertilizer applications should only be applied to active soils when soil temperatures are above 50° F.
• Applying lime to acid soils increases the P solubility in acid soils, but over-liming can reduce P solubility. Sorption also occurs to calcium cations (Ca²⁺) but only at pH values up to 6.5. At higher pH values, Ca-P precipitates form.
• Incorporating P into the soil when possible increases adsorption and reduces the amount of plant available P. Broadcasting P fertilizer on the surface leaves the fertilizer susceptible to runoff.

Plant Issues

• Returning clippings to the turf is a practical method of returning organic P back to the soil. Clippings may account for 0.10 to 0.35 lbs P per 1,000 sq. ft. If clippings are removed, the loss of P depletes available P for plant uptake.

Other Sources Issues

• Foliar applications at light rates may increase plant uptake. Unabsorbed foliar P, however, remains at risk for episodic losses due to runoff caused by heavy precipitation or excessive irrigation. A light irrigation after P fertilizer application has been shown to reduce P runoff.
• Phosphonate fungicides are chemically different from phosphonate fertilizers in that the fungicide provides a phosphite ion (H₂PO^3-) having one less oxygen atom. Potassium phosphite, also labeled as mono and di-potassium salts of phosphorus acid (Aliette, and Chipco Signature) are the most common examples of a phosphonate fungicides. No evidence suggests that the phosphite ion is used in the plants metabolism. Regardless, the amount of P supplied in any fungicide application is negligible.

6.5 Fertilizer Applications

Proper application of fertilizers is possible only with accurately calibrated sprayers or spreaders. Incorrectly calibrated equipment can easily apply too little or too much fertilizer, resulting in damaged turf, excess cost, and contamination of the environment. Therefore, sprayers and spreaders should be calibrated at first use and after every fourth application. The time it takes to calibrate application equipment is returned many fold in improved results.

An excellent resource for spreader care and calibration can be found on the Penn State Extension site. Spreaders should also be thoroughly cleaned after use due to the high salt content that corrodes metal parts. However, the wash water will likely contain N or P and should be disposed of properly.

6.6 Nutrient Management Best Management Practices

Soil Testing

• Maintain dense turf stand through proper nitrogen fertilization to reduce soil runoff.
• Because turf is extremely responsive to soil N status, evaluate changes in clipping yield during the growing season to estimate N availability.
• Monitor K and P by testing soil regularly.
• Conduct a soil test as required by the NYS Dishwasher Detergent and Fertilizer Law to confirm a need for phosphorus fertilization prior to its application.
• Sample when soils are biologically active. Fall sampling is most common and allows time to review results and apply lime and nutrients in advance of spring growth and to develop a season-long plan.
• Do not sample within the two months following heavy fertilizing or liming; sampling around frequent, light applications (spoon feeding) is acceptable.
• Test soils at the same time of year to allow for comparison of results from year to year.
• Because soils exhibit significant spatial variability, take a number of samples, combine, and then subsample. As a rule, a minimum of 10 sample locations should be sampled per acre.
• Sample areas with different soils and drainage separately. For instance, sample sand-based greens and tees separately from fairways and roughs.
• Take the sample from the root zone (typically 4-6 inches deep) by removing the grass mat from the top of the sample.
• Used in conjunction with soil tests, analyzing plant tissues over time can be used to observe trends that can be correlated to environmental and management factors.
• On sand based areas, consider foliar testing as a diagnostic tool.

Nutrient Management Planning

• Use N fertilizer to produce even growth rate. This increases golf course playability and minimizes the risk to the environment, while excessive fertilization reduces playability and increases the risk of N leaching.
• Use water soluble fertilizers at light rates of 0.5 lbs N/1,000 sq. ft in general; 0.4 lbs N/1,000 sq. ft on sand; and no more than 0.7 lbs N/1,000 sq. ft on other soils (assuming no heavy rain events) and more frequent applications.
• Lightly irrigate after P fertilizer application to reduce the potential for P runoff.
• Do not apply nutrients to saturated soil or prior to heavy rainfall, which can lead to significant off-site movement.
• Avoid N application too early in the spring or too late in the fall because it can increase soil nitrate levels and can pose a greater risk to groundwater quality.
• Reduce nutrient applications during summer decline when plant uptake decreases.

Fertilizer Applications

• Choose the appropriate type of spreader for a given fertilizer.

Calibrate application equipment every first use and after every fourth application.