Fertilizing

Building Your Fertility Program

Your goal as a turf manager should be to provide adequate nutrition that promotes turf density and in turn improves field safety and playing conditions. 

Many factors will influence the ultimate fertility program you develop including: grass species, soil type, time of year, intensity of field use, performance expectations, specific sport, budget, equipment, available labor, etc.

Some managers develop their sports field fertility program based on their experience, turf performance and generally accepted guidelines. 

However, routine soil testing that provides baseline information on the phosphorus, potassium status, pH and organic matter content coupled with tissue testing can add precision to your management decisions.

Soil testing

Soil testing is an important routine management practice and an essential tool when developing a fertilizer program that promotes good turf growth while protecting the environment.

For more information go to the Soil testing section. Keep in mind that turf will not benefit from the addition of fertilizer if there are adequate levels present in the soil and in the plant. Excess nitrogen applications will be harmful to turf growth and can have a negative environmental impact. Most New York soils have adequate levels of phosphorus so supplemental applications in most cases may not be necessary. When adequate soil levels of potassium (K) are present there is no benefit from applying more K. In fact high applications levels can inhibit root growth and excessive levels have been shown to increase the incidence of some diseases, like snow mold.

 

 

Necessary nutrients

Nitrogen (N), phosphorus (P) and potassium (K) are called “macronutrients” because they are needed by the plant in relatively large quantities.  Nitrogen (N) is the nutrient that primarily controls turf growth and density and is required in the largest amount. 

When adequate nitrogen is provided the turf will have a vigorous root system, high shoot density, maximum recuperative potential and tolerance to environmental stress. Also, varieties that have a color response to nitrogen will darken up when fertilized. Inadequate or low levels of nitrogen will reduce shoot density,  stress tolerances and ability to recover as fast from traffic damage, and favor weed encroachment and certain diseases like rust, red thread and dollar spot. Excessive amounts of nitrogen can be detrimental to the turf by reducing rooting, stress tolerance and wear tolerance. Excessive nitrogen can also increase thatch and favor diseases that thrive in high nutrient situations like snow mold, leaf spot and brown patch.

There is no reliable soil test for nitrogen so other factors are used in determining the amount of nitrogen that is needed. However, soils with more than 6% organic matter require less nitrogen. You can select nitrogen fertilizer sources that are water soluble and have quick release properties, fertilizers that have slow release properties or a combination of both.  See tables for advantages and disadvantages of different nitrogen sources. 

Advantages and disadvantages of nitrogen fertilizer sources

Nitrogen form Advantages Disadvantages

Quick release:

  • Urea
  • Ammoniacal N
  • Ammonium sulfate
  • Quick release, rapid response(within a week)
  • Minimal temperature dependency
  • Water soluble
  • Can be tank mixed (sprayed on)
  • Low cost
  • Short duration of response (peaks in 2 weeks, can last up to 6 weeks)
  • High salt index, can have foliar burn
  • Can leach or volatilize
  • Nitrogen losses can be greater

Slow release:

  • Sulfur Coated Urea   (SCU)
  • Polymer Coated Urea
  • Methylene Ureas
  • IBDU
  • Usually last 8-12 weeks, some 20
  • Low foliar burn potential
  • Reduced loss by leaching
  • Applied at higher rates less often
  • Higher cost per unit of nitrogen
  • Slow initial release rate
  • If bags damaged nutrients released
  • Microbial activity may be required for release

Slow release:

  • Natural Organics
  • Some contain other macro and micronutrients
  • Some improve soil properties
  • Some have disease suppressive activity
  • Slow initial release
  • Lower nitrogen content
  • Higher cost/unit of nitrogen
  • Nitrogen release is dependent on microorganisms, temperature and moisture dependent

Phosphorus 

Phosphorus (P) promotes rooting and is especially important in new seedings because it enhances establishment, especially with tall fescue. Phosphorus should be incorporated into the seedbed since it is not very mobile in the soil. Applications of phosphorus to established turf are rarely needed but applications of P may be necessary when overseeding. Soil test to determine needs.

The availability of phosphorus in the soil is influenced by pH. Phosphorus is most available at pHs above 6.5 so be sure to check your soil pH. 

Some common sources of phosphorus include superphosphate (16-21% P2O5), triple superphosphate (40-47%), Monammonium phosphate (48%) and Diammonium phosphate (46-53%).  A natural organic source is steamed bone meal (23-30%) and animal based composts.

Potassium

Potassium (K) promotes rooting, rhizome and stolon development and is said to improve heat, cold, wear and drought tolerance (although there is not enough research to back up this claim). It can help reduce some diseases such as leafspot, brown patch, red thread and dollar spot.

Potassium is very mobile in the soil and is easily leached in sandy soils.  So when soil tests determine potassium is needed it should be applied in smaller amounts several times during the year or applied in slow release forms especially on sandy fields. If soil test results are not available a minimum ratio of 2:1 (nitrogen: potassium) is desired. Common potassium sources include muriate of potash (KCL) with 60-62% K2O and sulfate of potash containing 50-53%.

Micro-nutrients for sports fields

Micro-nutrients are just important as macronutrients but are required in smaller amounts. They include iron (Fe), manganese (Mn), boron (B), molybdenum (Mo), zinc (Zn), copper (Cu), nickel (Ni) and chlorine (Cl). 
 
Sports turf managers either apply micro-nutrient packages based on soil test recommendations or because they are looking for “extra insurance”. Generally speaking, unless your soil has a very high pH (>8.0) or is very sandy in texture or low in organic matter it is unlikely that your soil will have a micronutrient deficiency.
 
Of all the micronutrients iron is the one we see the greatest response from greening.  Iron is an essential component of chlorophyll synthesis so it is not surprising to find chlorosis or turf yellowing in the youngest leaves if there is a deficiency. Regular applications of iron are usually essential for turf maintained on very alkaline (high pH) soils. Iron fertilizers can also be used to produce a dark green color without stimulating excessive leaf growth. A common practice for iron deficiencies is to apply a 1-2 ounce spray of ferrous sulfate per 1000 sq ft. Applications made when turf is growing rapidly enhance color for only 2-3 weeks, whereas applications made during periods of slow growth may last for several months. Organic products will provide a slower color response than inorganic sources like ferrous sulfate. Take care not to over do it! Excessive rates can cause a noticeable black-green color. When rates of inorganic sources were applied at greater than 5 lbs./acre, significant phytotoxicity (plant injury) was observed.

Before you consider using micro-nutrient packages as a routine practice, remember to check the soil pH. If it is in the 6.0 to 7.0 range micronutrients are usually found in sufficient amounts to support good turf quality. If the pH is high >8.0 sulfur can be used to lower the pH.  Use sulfur rates recommended by a soil test.  

Fertilizer terms

Complete fertilizers will have the 3 most important macronutrients nitrogen, phosphorus and potassium (N-P-K) and will be stated on the fertilizer bag.  The numbers on the bag are always written in the same order and indicate the fertilizer analysis which is the percent (%) of nitrogen, phosphorus (as an oxide P2O5) and potassium (as soluble potash K2O) by weight. In a 100 lb bag of 20-5-10, 20% would be the nitrogen (or 20 lbs), 5% would be the phosphorus source (or 5 lbs) and 10% would be the potassium source (or 10 lbs).  The remaining material is needed to help spread the fertilizer or may just be part of the N, P or K and not added to make if spread better.

Another fertilizer term worth knowing is fertilizer ratio.  That is the proportion of the nutrients to each other. A fertilizer with the analysis of 20-20-20 has a 1:1:1 ratio as does 30-30-30.  A fertilizer with a 20-5-10 analysis has a 4:1:2 ratio.

A starter fertilizer is one that has a higher percent of phosphorus which is beneficial at the time of seed establishment and overseeding if soils are low in P. Examples include: 18-24-12 and 16-25-12.

Commonly used abbreviations and symbols

Unit Abbreviation or symbol Examples
Ounces oz. Apply 5 oz. each time
Pound lb. or # Apply 3 lbs. or Apply 3#
Cubic Yards cu. yd. or yd3 Apply 75#/ cu. yd. or Apply 75#/yd3
Square feet sq. ft. of ft2 Apply 5#/ 1,000 sq. ft. or Apply 5# 1,000 ft2
Acre = 43,560 sq. ft. A Apply 500#/A

 

Nitrogen sources

Although N, P and K are all important nutrients, more attention is given to nitrogen because it is needed in the largest quantity and will give the greatest response.  Applying nitrogen during the playing season will significantly improve turf quality, growth and recovery. Water soluble nitrogen sources provide rapid response within days or a week (depending on temperature) and will typically last about 2-6 weeks.  Slow release or controlled release nitrogen sources offer an extend period of nutrition and can last 8-12 weeks and some even as long as 20 weeks.

Natural organic nitrogen sources come from plant and animal by-products or waste products. They are typically lower in nutrients, have little burn or leaching potential and require warm moist soils for availability. The rate of nitrogen release from organic sources does differ. Research from North Carolina State University found that over a 10 week period, Nature Safe (turkey manure and feathers) released 70% of its total nitrogen, Milorganite (bio-solids) 60% and Bion (hog waste) 20%.  Products containing proteins (meat, blood, feathers, fish meal, corn gluten meal) release more nitrogen than previously digested sources such as bio-solids and animal wastes.

Characteristics of common turfgrass nitrogen sources

Fertilizer Source Nitrogen Content % Leaching Potential1 Burn Potential2 Low Temp
Response3
Residual Effect4
Inorganic*
Ammonium sulfate 21 high high rapid short
Organic - Natural
Bio-solids 6 very low very low very low long
Manures 3-10 very low very low very low long
Natural products 3-12 low-very low very low low-very low mod-long
Organic – Synthetic
Urea 45-46 high high rapid short
Sulfur coated urea 22-37 low low moderate moderate
IBDU 31 mod-low low moderate moderate
Methylene ureas 38 low low very low mod-long
Urea formaldehydes 38 mod-low low low long

* Ammonium nitrate and Calcium nitrate.

1 Leaching potential – likelihood of the fertilizer moving beyond the root zone due to its solubility.

2 Burn potential – likelihood of turf injury due to the salt concentration of the fertilizer.

3 Low temperature response – the ability of the fertilizer to have an effect under low temperature    (50°- 60°, for example in the spring when early green up is desired.

4 Residual effect – estimates how long the fertilizer effect will last.  For example, water soluble   (quick release) fertilizers are short termed lasting between 2-8 weeks whereas slow release  fertilizers may last up to 4 months or more.

Nitrogen timing and rates

When establishing a new stand of turf on sandy type soils apply 0.4 pound of a soluble nitrogen  per 1,000 sq. ft. or up to 1 pound of total nitrogen with fertilizers with at least 60% slow release nitrogen. If in 4-6 weeks the turf is not dense and it is before November 1st make another application at the same rate. If it is after November 1st wait until mid-May to make this application.

On non-sandy soils apply 0.7 pound of a soluble nitrogen  per 1,000 sq. ft. or up to 1 pound of total nitrogen with fertilizers with at least 30% slow release nitrogen. If in 4-6 weeks the turf is not dense and it is before November 1st make another application at the same rate or less.  If it is after November 1st wait until mid-May to make this application.

Fertilizing established turf

Understanding how cool season grasses grow and develop will help in understanding the strategy behind specific timing of established turf.

Focus your fertility program on building a healthy root system. Sixty percent (60%) of your fertilizer applications should be made in the fall when the roots can benefit from it the most. An extensive root system is better able to survive stress next summer.

When a fall application was not made and spring sports are planned a light nitrogen application can be done in early spring after April 1st. Heavy spring fertilizer applications, however, lead to excessive shoot and leaf growth and poor root growth.  This leaves the turf less likely to handle the harsh summer conditions.

Unless you are irrigating the turf there may be little or no need to fertilize in the summer if it is dry. If an early summer application is desired to repair damaged fields from spring use, select a slow release type like a natural organic source which release nitrogen slower than conventional water soluble sources.

A late summer fertilizer application (mid-August) is important because it promotes recovery from the summer's drought and heat related stress. Select a fertilizer with a 50:50 water soluble N: slow release form and apply at the ¾ -1 lb nitrogen rate per 1000 sq. ft.

Early fall fertilization (September) increases turf density by encouraging the production of new tillers, rhizomes and stolons and more shoot growth from existing turf. The production of carbohydrates at this time will help turf survive the stresses of winter and encourage spring growth.  October fertilization will maximize turf growth and recovery from fall sports.

Fertilizing turf when the soil is not frozen and when foliar growth slows down (when air temperatures are <50° for 10 days) contributes to significant root, rhizome and stolon growth.

Also, turf color is extended into the late fall and early winter and early spring green up is promoted. Be careful, however, with late season nitrogen applications on sites with ground water issues, like Long Island. Follow state and local laws on the last date to apply fertilizer which may be November 1st or November 15th in your area. If you choose this option select a nitrogen source that is not temperature dependent, like IBDU and SCU and apply at the ¾ lb. rate or urea at the ½ lb. per 1,000 sq. ft. nitrogen rate. 

Sample fertilizer program for football fields

Situation: no spring sports on this field
Minimal management field rates are bolded
High management fields rates are in red

Timing Nitrogen rate
per 1,000 sq. ft.
Nitrogen
source
Comments and strategy
Before April 1st     Do not apply fertilizer.
Early spring     If late fall fertilization applied previous year, early fertilization may not be needed
Mid-late May 1#
1#
50% water soluble or use a 100% organic source Warm soil temperatures release nutrients.
Organic sources build up soil nitrogen and feed microorganisms.
July     No need to fertilize especially if fields are not irrigated.
Mid-August 1#
1#
50% water soluble Apply just before the season begins.
Mid-September 1# 50% water soluble  
Mid-October ½ # 100% water soluble  
November     New York State or local laws may prohibit application of fertilizer at this time.