Figuring out Fertilizer. (High Science)

Article excerpt

Sixteen elements are essential for normal turfgrass growth. A deficiency in any one, regardless of the amount required by plants, can interfere with normal plant growth.

* soils do not normally contain high levels of nitrogen;

Nitrogen (N) is required in the largest amount of any of the other nutrients, making up 3 to 6 percent of the dry matter. It is a component of the green pigment in plants (chlorophyll). Nitrogen is more likely to be deficient than the other 15 elements for several reasons:

* nitrogen applied as fertilizer may be lost because of leaching and volatilization;

* sandy soils are prone to leaching where irrigation occurs frequently; and

* clipping removal leads to nitrogen depletion.

Nitrogen affects turf performance in seven ways:

1 It will increase the rate of shoot growth.

2 It will increase root growth when added to a nitrogen-deficient soil. Too much nitrogen can actually decrease root growth by forcing top growth at the expense of shoot growth.

3 It promotes tillering, plus rhizome and stolon production that creates thicker, more dense stands.

4 It will affect disease proneness. Some diseases (leaf spot, brown patch, pythium blight, snow molds) are favored by high nitrogen levels. Diseases favored by low nitrogen levels include dollarspot, red thread, rust and anthracnose.

5 It will improve heat, cold and drought tolerance going from a deficiency to a sufficiency level. Again, too much nitrogen can decrease tolerance to these stresses.

6 It will improve the ability of turfgrass to recover from injury by forcing new growth.

7 It will affect the composition of the turfgrass community when grass mixtures are planted. For example, higher N rates will favor Kentucky bluegrass when planted in mixtures. Also, properly fertilized turf areas will help prevent weed invasion.

Nitrogen sources

Nitrogen sources are usually classified by the [timing of the] availability of nitrogen: quick release and slow release.

Quick-release fertilizers contain nitrogen in either the nitrate or ammonium forms which are readily available for plant uptake. These fertilizers are often called water-soluble because they will dissolve in water. Quick-release N sources commonly used for turf include urea, ammonium nitrate, ammonium sulfate and ammoniated phosphates.

Slow-release fertilizers -- sometimes called controlled-release or water insoluble fertilizers -- may be divided into three main groups: synthetic organics (such as ureaformaldehyde and IBDU), natural organics (derived from any naturally occurring plant or animal by-products) and coated materials (such as sulfur-coated urea and the newer polymer-coated products). Generally slow-release sources aie applied at higher rates, less frequently.

Phosphorus (P) is a component of ATP, which is a chemical in the plant that holds and transfer energy. It affects turf performance in five ways:

P and K

1 It will promote rooting.

2 It's especially important in new seedings because it enhance establishment.

3 It will hasten maturation (important in seed production).

4 It is important in reproduction (for seed prod production).

5 It will influence the composition of the turfgrass community (higher rates tend to favor Poa annua). …