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Demystifying Turf Fertilization

Nothing says “baseball season” like a sward of lush, green grass! For many schools and parks, a baseball or softball field sporting dense, uniform turf seems more of a lofty fantasy than a realistic goal. In fact, this dream is not as far-fetched as most believe. In this article, we’ll examine the number one “bang-for-your-buck” practice in turf management: fertilization.

Applying fertilizer is often referred to as “feeding” the grass. In fact, the grass doesn’t need to be “fed” – plants make their own food through photosynthesis – but by adding the proper nutrients to the soil, we can help the grass produce sugars more effectively. The three major nutrients included in fertilizers are nitrogen, phosphorous, and potassium. These elements are typically abbreviated as N, P, and K.


Figure 1. A huge improvement in the quality of most athletic fields can be gained simply by applying enough fertilizer.

Most soils in the Midwest were previously used for agriculture, and still contain an abundant supply of P and K. This is fortunate for turf managers, because in many cases we do not need to add any P or K to the soil. In fact it is illegal in Wisconsin to apply P unless you have a soil test demonstrating low levels. The best way to determine how much P and K fertilizer to apply is with a laboratory soil test. These tests are inexpensive (~ $10) and are available through UW Extension or many private labs. H&K Sports Fields can also help you submit and interpret a soil test.


Figure 2. A soil probe is the best tool for taking samples, but a trowel or spade will also work. Keep the sampling depth consistent and take 10-12 samples per acre; after mixing these plugs together, submit a composite sample to your lab of choice.

Nitrogen is very different from P and K. Unlike phosphorous and potassium, N does not remain in the soil but is quickly consumed by plants and soil microbes. Grass plants require more N than most broadleaf weeds so unless we add fertilizer the desirable grasses can be overtaken by dandelions, clover, and plantains.

So applying nitrogen benefits the grass, but how much should we add? Research by UW Madison turfgrass scientists shows that grass growth peaks at an annual rate of 12 pounds of nitrogen per 1,000 square feet. This is an extraordinary amount of fertilizer!! Fortunately, our goal as turf managers isn’t to maximize growth- it’s to provide a uniform playing surface with good visual appeal. So unless you want to mow your field every day (or twice a day!) please don’t apply this much N. For baseball and softball fields in Wisconsin a good starting point is approximately 4 pounds of nitrogen per thousand square feet each year. This rate is sufficient to encourage vigorous growth and a lush green color without requiring excessive mowing. Unless you are using a slow-release N source, the applications should be made at no more than 1 pound of N per 1,000 square feet at a time.

What’s the best kind of fertilizer to buy for your field? That depends on the individual scenario, but it’s best to keep things simple. The grass doesn’t know whether a fertilizer comes in a fancy, bright-colored package, nor does the grass care whether the fertilizer has proprietary formulations and complicated additives. Many agricultural grade fertilizers are perfectly sufficient for fertilizing turfgrass. Urea, ammonium sulfate, and potassium nitrate are examples of cheap, effective N sources. When used sensibly, these products produce an excellent turf response and pose little environmental hazard. Perhaps 90% of recreational facilities are not supplying enough nitrogen to their turf. This really can’t be stressed enough!


Figure 3. Simple types of fertilizer are usually sufficient for turfgrass – urea and ammonium sulfate are two excellent sources of nitrogen, although they must be applied carefully and watered in to avoid burning the turf.

Fertilization (especially with nitrogen) is the cheapest way to make your field stand out visually, and to produce a safer, more uniform playing surface. In future editions of the H&K Maintenance Minute, we’ll examine other simple turf management tips to help your field sparkle!

For more information on developing a fertilization program for your own facility, contact H&K’s Evan Mascitti at evan@HKSportsFields.com.