Turfgrass Fertilization Basics
A Guide to Turfgrass Maintenance Fertilization
First, a soil test should be made to establish the basis for a regular fertilization program. Soil testing service is available from Penn State's Agricultural Analytical Services Laboratory and from private testing laboratories. Soil test mailing kits for university testing may be obtained from county Extension offices at a nominal cost. The soil sample is forwarded to the university. After analysis, recommendations for fertilization are made.
Grass plants normally need nitrogen, phosphorus, and potassium (potash) in larger amounts than can be supplied naturally from the soil. Nitrogen, which is essential for vegetative growth and good green color, is a constituent of plant proteins, chlorophyll, amino acids, and other plant substances. Phosphorus is necessary for good root development and important in many vital growth processes. Potassium is required for physiological functions and promotes disease resistance, drought tolerance, and winter hardiness in grasses.
Fertilizer should be purchased on the basis of its quality rather than on bag size and price. Value depends on the total amount of plant food contained in the bag and the source of the nitrogen-carrying portion of the fertilizer. The law requires that the total amount of plant nutrients be listed on the bag. If the fertilizer contains slow release nitrogen materials, the percent water-insoluble nitrogen or controlled-release nitrogen must also be listed on the bag.
Complete fertilizer. A complete fertilizer contains the three major fertilizer elements--nitrogen, phosphorus (phosphate), and potassium (potash).
Fertilizer grade. The fertilizer grade designates the percentages of nitrogen, phosphate, and potash in the product. A 20-5-10 grade fertilizer contains 20 percent nitrogen, five percent phosphates and 10 percent potash. Thus, a 40-lb bag of 20-5-10 contains eight lb of nitrogen (20 percent of 40), two lb of phosphate (five percent of 40), and four lb of potash (10 percent of 40). The law requires that the grade be listed on the container and always in the order of nitrogen, phosphate, and potash.
Fertilizer ratio. The fertilizer ratio indicates the relationship among the percentages of nitrogen, phosphate, and potash found in fertilizer. A 10-5-5 grade contains twice as much nitrogen as phosphate or potash and has a 2-1-1 ratio. Grades of 16-8-8 and 20-10-10 also have a 2-1-1 ratio. A grade of 12-4-8 has a 3-1-2 ratio. A ratio may be determined by dividing each number of the fertilizer grade by the lowest number of the grade.
Liquid fertilizer. Fluids in which fertilizer nutrients are in true solution are liquid fertilizers. However, this term is applied also to suspension and slurry fertilizers, which are fluid mixtures containing dissolved and undissolved plant nutrients. Unlike true liquid fertilizers, they require continuous mechanical agitation during application. The value of these materials is based on the grade and weight of the liquid rather than on the fluid content. The law requires the weight to be listed on the container. The plant nutrient content may be calculated in the same manner as dry fertilizers. If, for example, a gallon of 10-5-5 liquid fertilizer weighs 10.5 lbs, then that gallon contains 1.05 lbs of nitrogen (10 percent of 10.5), 0.525 lbs of phosphate (five percent of 10.5), and 0.525 lbs of potash (five percent of 10.5).
Flowable fertilizer. Fertilizer nutrients of extremely small particle size are carried in liquid suspension. Because of the particle size and added suspension agents, they do not require constant mechanical agitation during application.
Water insoluble and controlled-release nitrogen. A fertilizer bag may carry the following label:
20-10-10, Guaranteed Analysis
Total Nitrogen 20 percent
10 percent Urea Nitrogen
2 percent Ammoniacal Nitrogen
8 percent Water Insoluble Nitrogen
Available Phosphates 10 percent
Water Soluble Potash 10 percent
In this example, the 20 percent represents the total percentage of nitrogen contained in the bag. The 10 percent urea and two percent ammoniacal nitrogen represent the total percentage (12%) of soluble nitrogen in the bag. The eight percent water insoluble nitrogen represents the total percentage of nitrogen in the bag that is water insoluble or slowly available. The percentage of the total nitrogen that is water insoluble can be calculated from this label information. This value can be obtained by dividing the percentage of water-insoluble nitrogen indicated by the total percentage of nitrogen contained in the bag (also indicated on the label) and multiplying by 100. In this case, 8 percent ÷ 20 percent × 100, or 40 percent of the total nitrogen is water insoluble.
Proper liming is essential to a sound fertilization program. Lime should be applied in accordance with a soil test. Proper liming creates a favorable soil environment for plant growth and keeps plant nutrients available for plant use. Liming, therefore, provides the most efficient use of applied fertilizer materials.
Again, it must be emphasized that a soil test to determine fertilizer requirements provides the best guide for proper fertilization. When soil tests are not used, one of the following suggested programs can be followed. These suggestions are for average soil conditions and must be supplemented with additional fertilizer where soils are deficient in phosphorus and/or potassium.
Where the fertilizer contains 30 percent or more of the total nitrogen as water insoluble or controlled-release nitrogen:
Apply in late spring 1.5-0.5-0.5 lb of nitrogen, phosphate, and potash per 1,000 sq ft. Apply in early fall 1.5-1.0-1.0 lb of nitrogen, phosphate, and potash per 1,000 sq ft.
Where the fertilizer used contains 15 percent to 29 percent of the total nitrogen as water insoluble or controlled-release nitrogen:
Apply in late spring 1.0-0.5-0.5 lbs of nitrogen, phosphate, and potash per 1,000 sq ft.
Apply in late summer and again in late fall 1.25-0.5-0.5 lbs of nitrogen, phosphate, and potash per 1,000 sq ft.
Where the fertilizer used contains less than 15 percent of the total nitrogen as water insoluble or controlled-release nitrogen:
Apply in midspring and again in early summer 0.75-0.25-0.25 lb of nitrogen, phosphate, and potash per 1,000 sq ft.
Apply in late summer and again in late fall 1.0-0.5-0.5 lb of nitrogen, phosphate, and potash per 1,000 sq ft.
The preceding article was prepared by Peter J. Landschoot, Professor of Turfgrass Science, Department of Plant Science, The Pennsylvania State University, University Park, Pennsylvania.