AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Fall 1998, No. 7
Nitrogen is required in the largest quantities of all of the plant essential mineral elements and is often the most limiting nutrient in turfgrass growth. The most obvious result of nitrogen fertilization is rapid green up and an increase in shoot growth and overall turf density. Nitrogen nutrition also affects root growth, stress tolerance, recuperative potential, and weed encroachment.
Nitrogen fertilizers used on turf are classed as quick release or slow release. Quick release sources like ammonium sulfate, urea, and ammonium nitrate tend to cause flushes of growth that last for only a few weeks. Therefore, the most effective way to apply quick release nitrogen fertilizers is by "spoon feeding" in frequent applications. Slow release nitrogen sources like sulfur coated urea, IBDU, and ureaformaldehyde provide a way to avoid the more erratic growth cycles encountered with quick release sources.
Phosphorus is an important component of turfgrass nutrition. Sufficient phosphorus fertility of turfgrasses is associated with increased root growth and branching, increased tillering, hastened maturity, reduced encroachment of some weed species, and improved drought tolerance and recovery. Excessive phosphorus applications have in some cases been related to annual bluegrass (Poa annua) encroachment.
Turfgrasses require large amounts of potassium. Potassium is second only to nitrogen in the amounts required by turfgrass plants. Soil potassium can be quickly depleted under turf. Therefore, frequent applications of potassium fertilizer are usually necessary to achieve optimum performance. The recommended rate of potash fertilization can be as much as twice that of nitrogen in some cases. Proper potassium fertility management has been shown to be associated with increased disease resistance, increased cold and heat tolerance, and improved overall ability to endure stressful conditions. Adequate potassium levels improve the winterhardiness of warm season grasses such as bermudagrasses and the heat tolerance of cool season grasses like bentgrass. Satisfactory levels of potassium produce turf that is more likely to endure stressful conditions such as drought and excessive traffic.
Secondary and micronutrient fertilization is often essential in the production of healthy turf. For example, turfgrass color is often improved with foliar application of iron.
Balanced fertility management can reduce the risk of encountering many problems in turf production. Soil and tissue tests in conjunction with field observation should be used in determining the need for all nutrients.