Fertilization practices affect growth rate, density, color, drought tolerance, disease activity and putting quality of golf greens. Ideally, nutrients should be available to the grass in amounts needed to maintain growth and color without increasing susceptibility to drought and disease and without increasing grain and thatch. Realistically, the superintendent should maintain adequate levels of phosphorous, potassium and minor nutrients in the soils and provide nitrogen and iron as the grass requires.
Soil test and plant tissue analyses help the superintendent monitor the amount and availability of phosphorus, potassium and minor nutrients. However, visual observations of color and density and clipping removal are essential for estimating nitrogen needs. Soil tests and tissue analyses alone are not enough to determine nitrogen needs on putting greens.
Considerable expertise is required of the superintendent to maintain healthy, dense turf and good color without developing “lush” growth. While grass species, environmental conditions, greens construction and cultural practices influence the nitrogen requirements of putting green turf, the superintendent must evaluate all of these factors to maintain the required level of nitrogen.
Organic and slow-release nitrogen sources should be used to provide small amounts of soluble nitrogen over a longer time period. For maintenance, soluble nitrogen should be applied at rates less than 0.5 pound per 1,000 sq. ft. on bermudagrass and 0.3 pound on bentgrass. Slow-release products such as sulfur-coated urea, IBDU and ureaformaldehyde can be applied in combination with soluble nitrogen sources to extend the period of nitrogen availability.
Potassium’s importance as a major fertilizer nutrient is often overlooked on putting greens. Researchers consistently show grass responses to potassium to include root growth, drought tolerance, disease resistance, wear tolerance and color on putting green turf. These responses to applications of potassium are observed even where soil levels of potassium are adequate. Research at Ohio State University suggests that potassium applications may reduce the requirements of bentgrass for nitrogen. Thus, some of the desired responses to fertilization such as root growth, color and disease tolerance can be produced without the excess growth associated with nitrogen applications.
Since potassium losses on greens are similar to those of nitrogen, light and frequent applications of potassium are required to maintain its availability to the grass. On golf greens, potassium should be applied at about the same rate and frequency as nitrogen.
Relative to nitrogen and potassium, lower levels of phosphorus are required for greens maintenance. Also, phosphorus accumulates in the soil, whereas nitrogen and potassium are readily leached below the rootzone of grasses. Under most conditions, two or three applications of phosphorus per year are adequate for either bermudagrass or bentgrass greens.
Since iron is readily tied-up in alkaline soils, and not available to the grass, light and frequent applications of iron are required to maintain its availability on most greens. Monthly applications of iron sulfate or iron chelate required under conditions where iron is not readily available to the grass.