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Fertilizing Lawns

Fertilizing Lawns

Posted - Apr. 16, 2004 at 1:23 p.m.



This archived news story is available only for your personal, non-commercial use. Information in the story may be outdated or superseded by additional information. Reading or replaying the story in its archived form does not constitute a republication of the story.

Larry A. Sagers Regional Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved

The beautiful green lawns that surround many Utah homes are important parts of our landscapes. Dozens of growth factors including light, water, pest control, soils and fertilizers play an important part in keeping the turfgrass beautiful.

Most homeowners never worry about their lawn until something goes wrong. They simply want them to sit there, look good and shut up. In short, lawns are the Rodney Dangerfield of the landscape because they “don’t get no respect.” The only time anyone becomes concerned is when they have problems.

The goal of any homeowner is to produce turf that is attractive, healthy, and able to withstand the rigors of use. While all the factors are important, a professional turfgrass manager soon learns all are interrelated. All inputs, whether natural or manmade have to be balanced.

This concept, called the “rule of limiting factors” is best illustrated by comparing the inputs in a lawn care program to the staves of a wooden barrel. If the barrel staves represent each growth factor, the barrel will never be filled unless each stave is full length. In other words, whatever growth factor represented by the barrel stave is most limiting, determines how well the grass is going to grow.

Fertilization is one growth factor represented as a stave on the barrel. Adequate nutrition is one basic component of any turfgrass management program. Correct fertilization determines the turf color, density, uniformity and growth rate. Fertilization helps turf compete with invading weeds and helps it withstand environmental and biotic stresses including fungi, insects and other pests. Turfgrass requires 16 chemical elements for growth and development. All are essential, but there is a great difference in the amounts needed for healthy turf growth.

Living grass plants are mostly water – with a small amount of solid or dry matter composed of the 16 essential nutrients. Plant physiologists divide these essential plant nutrients into two main groups based on where the turfgrass gets them. These are air or water supplied nutrients, and soil or fertilizer supplied nutrients.

The first group, carbon (C), hydrogen (H), and oxygen (O), come from atmospheric carbon dioxide and water and comprise 90- 98% of the grass plant. Quantity-wise these three nutrients account for many times the percentage of the other nutrients. Mother Nature supplies them if the turf is otherwise cared for properly.

The second group is minerals derived from the soil or as fertilizer nutrients. This group subdivided into three groups based on the quantities of the elements used by the turfgrass.

Nitrogen (N), phosphorus (P), and potassium (K) are macronutrients because the turf uses them in relatively large quantities. However, in terms of the total weight of the plant their amount is still very small.

Secondary nutrients include sulfur (S), calcium (Ca), and magnesium (Mg). These are used in smaller amounts by turfgrass plants. The need to apply these fertilizers varies greatly depending on the soil type and the growing area. Utah soils often have excessively high amounts of calcium and magnesium.

Micronutrients, as the name implies, are used in much smaller amounts by the turf. They are often referred to as trace minerals. Micronutrient never means unimportant. These nutrients are (Fe), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), boron (B), and chlorine (Cl) and are used in the smallest amounts by the plants.

The following chart gives relative amounts of nutrients that the turf uses. It gives the element ranges that normally occur in turfgrass as determined by tissue analysis. Maintaining nutrient levels in these ranges keeps turf healthy, dense, and vigorous.

Of these mineral elements, nitrogen, potassium, phosphorus, sulfur, and iron are most commonly applied to turf. Most soils supply adequate quantities of other secondary nutrients and micronutrients. Applying nitrogen, potassium, phosphorus, sulfur, and iron triggers specific growth responses in turfgrass.

Turfgrass Mineral Composition

Dry weight Percentage Nitrogen (N) 3 to 6 Phosphorus (P) 0.4 to 0.8 Potassium (K)2 to 4 Iron (Fe)0.1 to 0.3

Except for nitrogen and potassium, none of the soil-supplied nutrients ever comprises more than one percent of the plant. Most are present in much lower amounts.

Some recommendations erroneously include regular applications of micronutrients. Never apply micronutrients without reason. Visual deficiency symptoms on the turf or reliable soil tests must show the need to apply the nutrients.

Even small amounts of micronutrients applied unnecessarily can cause serious toxicity problems. Overusing micronutrients ties up and adversely affects the uptake of other nutrients. In addition, there are no easy ways to remove toxic nutrients from the soil nor are there antidotes for the problems.

In addition to the amount of nutrients in the soil, nutrient availability is an important issue. It is essential to consider aeration, temperature, moisture, pH and other related factors when outlining a turf fertilization program.

Never apply a fertilizer without considering its effect on the level of nutrients present, the availability of nutrients, or the interactions with all environmental factors. Indiscriminate application of unneeded nutrients increases turf nutrition problems and in some cases makes it impossible to correct the difficulties.

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