DEVELOPING A FERTILIZER PROGRAM FOR TURF
, 8 min reading time
Fertilization is very important for the maintenance of most quality turf areas. It is the process of applying essential nutrient elements for the growth and development of grass. There are a few highly fertile soils where regular fertilization may not be required, but most of us are going to need at least some fertilizer for proper maintenance of our turf areas. So, what is needed, how much do I need, and when should it be applied.
The term fertilizer can refer to many different materials that provide essential elements for the growth of plants. There are currently 17 elements considered essential for all plants. They include the following elements: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), magnesium (Mg), and calcium (Ca) are macronutrients, whereas molybdenum (Mo), copper (Cu), zinc (Zn), manganese (Mn), boron (B), iron (Fe), chlorine (Cl), and nickel (Ni) are termed micronutrients. The carbon, hydrogen, and oxygen are obtained from the air and water, but the others are generally taken up by the roots from the soil.
Nitrogen (N) is generally the limiting factor in most turf soils and will be the element applied in the greatest quantity. In fact, most fertilizer programs for turf areas are based on the amount of N to be applied each year. The exception is at the time of establishment, where fertilizers high in phosphorus (P) are generally required. These are called starter fertilizers. (See WHAT IS A STARTER FERTILIZER IN THIS SERIES).
A good place to start in developing a fertilizer program is to take a soil test. Begin by taking a representative sample from the soil to a 3-inch depth. Collect samples from several locations in the lawn, mix them together and take a subsample of approximately a cup of soil. In many locations, the local extension office can help you with where to submit the sample. Many universities perform the service for a fee. If that is not available, you may have to go to a private laboratory in your area. Information on these private labs will generally be available online. Again, there will be a reasonable fee for the service. These soil tests do not provide useful information on nitrogen requirements, but they can tell you if any of the other elements are limited and will help you determine which fertilizer to buy.
The most important elements supplied by a commercial fertilizer are generally N (nitrogen), P (phosphorus), and K (potassium), although you may find some types that include iron, magnesium, or some of the other minor elements. All fertilizers sold in the United States use a standard system for listing the elements and the amount of each element found in the container. This is done by listing three numbers on the label. For example, a 50 lb. bag of fertilizer may have the following numbers listed in a prominent location on the front of the bag:
25-5-15
These numbers are called the “analysis” of the fertilizer. They represent the percentage by weight of three distinct materials. They are N, P2O5, and K2O. Notice that this is not N-P-K. In the example above, the fertilizer would contain 25% by weight N, 5% by weight P2O5, and 15% by weight K2O.
To determine how much of the elements P and K are in the fertilizer, the following conversion factors are needed:
P2O5 x 0.44 = P
K2O x 0.83 = K
In the above example, a 50 lb bag would contain
50 x .25 = 12.5 lbs. N,
50 x .05 = 2.5 lbs. P2O5
and 50 x .15 = 7.5 lbs. K2O.
To convert the P2O5 to P, multiply the
2.5 lbs of. P2O5 by .44 = 1.1 lbs P,
and the
7.5 lbs K2O by .83 = 6.2 lbs. K.
The bag of fertilizer then contains 12.5 lbs. of N, 1.1 lbs. P, and 6.2 lbs. K. This sounds unnecessarily complicated, but it is the way all fertilizers in the US are sold.
When buying fertilizers, the analysis will be critical in determining how much fertilizer is needed for a particular area. The recommendation for fertilizer needs is generally expressed on the amount of N per unit area. For instance, 1 lb. of N/1000 sq. ft. is often recommended. But that does not answer the question of how much actual fertilizer to apply. If I need 1 lb. of N/1000 sq. ft. and I’m using a 25-5-15, one lb. of fertilizer will not be near enough because the fertilizer is only 25% N. To determine how much fertilizer is needed to get 1 lb. of N, use the following equation:
X .25 =1 lb. N
In this equation, X is the amount of fertilizer that will be needed/1000 sq. ft. and .25 is the percentage of N in the fertilizer. It is solved by dividing both sides of the equation by .25. This results in 1 divided by .25.
X = 1/.25
X = 4 lbs. fertilizer
In this example, 4 lbs. of 25-5-15 fertilizer would need to be applied per 1000 sq. ft. to attain a rate of 1 lb. N/1000 sq. ft. For more information see The Mathematics of Turfgrass Maintenance (http://www.amazon.com/Nick-Edward-Christians/e/B001H6SB7A/ref=ntt_dp_epwbk_0).
So, how much fertilizer should you apply and when should it be applied? As is the case with most things in turf management, the answer is “it depends”. In this case, it depends on the type of grass your growing, the soil type on the area, and the local climatic conditions.
In most situations, do not apply more than 1 lb. N/1000 sq. ft. in a single application. Nitrogen can burn turf and excessive amounts can cause serious damage. The exception to this is certain slow-release fertilizers that have a lower burn potential, but most N sources will burn the grass if over-applied. In very hot conditions, you may need to reduce this to one half lb. or less. But generally, it is a good idea to wait for cooler weather to apply fertilizer.
For cool-season grasses, on clay-loam soils, 3 to 4 lbs. of N/1000 sq. ft. per season will generally be enough to maintain a high-quality turf. Not more than 1.5 lbs. N of this should be applied in the spring and the rest in late summer or fall. Avoid the high temperatures of mid-summer when the cool-season grasses are undergoing slow growth and burn will likely be a problem. A standard program would include 0.75 lb. N/1000 sq. ft. in April in combination with a preemrgence herbicide. An additional 0.75 lb. N would be applied about 4 weeks later before the hot weather sets in. In mid-to-late August, apply 1 lb. N/1000 sq. ft. Follow up 4 to 6 weeks later with 1 lb. N. This is a total of 3 lbs. N./1000 sq. ft. If the season has been unusually wet or the soil has a lot of sand, an additional lb. can be applied in late October to early November for a total of 4 lbs./1000 sq. ft. for the season. On very fertile soils, you may be able to get by with less than 3 lbs. for the season and on very sandy soils and wet conditions, more than 4 lbs. N may be needed. But the standard 3 to 4 lb. N. program will be fine for most areas in the cool-season zone.
For warm-season grasses, the standard recommendation is 1 lb. of N/1000 sq. ft. per growing month. In the central part of the country, where growing seasons are shorter, three-monthly applications may be enough and in more southern regions, 4 to 5 monthly applications may be necessary. As with cool-season grasses, a little less will be fine on highly fertile soils and more may be needed on sandy soils and in wet conditions. For more detailed information on fertilizers programs for your region, contact your local extension service. Also, see Fundamentals of Turfgrass Management for more detailed information (http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html).
It is a good idea to use a fertilizer with some P and K. A material like 25-3-15 or 20-3-10, or some similar analysis will be appropriate for most soils. On high pH soils, some iron (Fe) may be required and on sandy soils with a low pH, magnesium (Mg) may be required. This is where the soil test will become useful for fine-tuning the program for your particular site.
Nick Christians, University Professor of Horticulture, Emeritus, Iowa State University
books: Nick Christians, University Professor of Horticulture, Emeritus, Iowa State University
books: http://www.amazon.com/Nick-Edward-Christians/e/B001H6SB7A/ref=ntt_dp_epwbk_0
turf blog: http://www.iaturf.blogspot.com/
Fundamentals of Turfgrass Mgt. 5th ed http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html
Web site: https://www.hort.iastate.edu/directory/nick-christians/
turf blog: http://www.iaturf.blogspot.com/
Fundamentals of Turfgrass Mgt. 5th ed http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html
Web site: https://www.hort.iastate.edu/directory/nick-christians/