The nitrogen cycle in turfgrass can be quite complex. Nitrate is taken up through the roots, converted into protein in the leaves, recycled as ammonium as grass clippings decompose and taken up again as nitrate. Nitrogen maybe recycled three to five times during the growing season. Nitrate in the soil is also subject to denitrification, volatilization, leaching and runoff.

Major Nutrients.Nitrogen NH 4 +, NO 3 -.Phosphorus H 2 PO 4 -.Potassium K + The major fertilizer nutrients include nitrogen, phosphorus, and potassium. In the fertilizer analysis nitrogen is always expressed as percent elemental nitrogen, phosphorus as percent HPO, and Potassium as percent K +.

Phosphorus is rarely limiting in turfgrass production, however in sandy root zones under irrigated conditions it can become limiting. Turfgrasses do not respond to excessive application of phosphorus in terms of color or growth. Excessive phosphorus can lead to deficiencies of minor elements, especially iron.

Phosphorus deficiency would appear as weak, thin turf and may display a purple pigmentation. This color symptom is often apparent in newly seeded bermudagrass that is planted too early or that is watered excessively. Phosphorus is not available to the grass under saturated soils or under low temperatures. Phosphorus levels of.3 to.5 percent in plant tissue are adequate.

Phosphorus, H 2 PO 4 -.Soil minerals.Organic matter.Fertilizers 3Small amounts present in soil 3Very slowly available 3readily filled by Ca, Fe, Al & microorganisms Phosphorus is made available to the plant through decomposition of soil minerals and organic matter and as fertilizers supplement. Phosphorus tends to accumulate in fertilized turfgrasses since it is not subject to leaching or volitalization.

P availability influenced by:.pH.Soluble Fe, Al (low soil pH).Soluble Ca (high soil pH).Amount of organic matter.Activity of microorganisms Phosphorus is most available at a pH range of 6 to 7.5.

The typical appearance of a seedling bermudagrass showing phosphorus deficiency.

Potassium, K + Often present in large amounts:.Soil minerals.Organic matter In clay or clay loam soils, potassium is usually present in adequate quantities. In sandy root zones, potassium is a limiting nutrient. Fertilizer applications provide the major source of potassium to turfgrasses.

Turfgrasses appear chlorotic and thin under low potassium levels. Such grasses are also subject to severe wear and weed invasions. Potassium levels are adequate at 1.5 percent or greater. However, on sports fields or high traffic areas 2 percent potassium in plant tissue is desirable. Once the potassium level is adequate grasses do not respond in terms of color or growth to additional potassium.

With low levels of K in plant tissue grasses appear chlorotic and weak. Such grasses are subject to severe wear.