Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, September 8, 1994 TAG: 9409080045
SECTION: CURRENT PAGE: NRV-12 EDITION: NEW RIVER VALLEY
SOURCE: JOE HUNNINGS
DATELINE: LENGTH: Long
Fertilizer Analysis
Many brands and formulations of lawn fertilizers are available. A basic understanding of what the numbers on the bag mean can help you decide which type of fertilizer is best for your lawn. Fertilizers are identified by their analysis, that is, the three numbers on the bag. The numbers refer to the percentage of nitrogen, phosphorus (expressed as P205), and potassium (expressed as K20) in the fertilizer. A 100 pound. bag of 29-4-8 contains 29 percent nitrogen, 4 percent phosphate, and 8 percent potash, or converted to weight, 29 pounds. nitrogen, 4 pounds. phosphate, and 8 pounds potash. The rest is inert ingredients, included to help distribute the nutrients evenly.
Nutrients
Nitrogen can really "green up" a lawn. However, some forms of it are very mobile and can leach through the soil to contaminate the water supply if not properly applied. The nitrate form of nitrogen (N03) can move with the soil water and contribute to pollution and algae blooms; it is of greatest concern in water quality. The positively charged ammonium form of nitrogen (NH4) can attach to the negatively charged soil particles and remain in the soil, but oxidizes to the nitrate form rapidly. There is a form of nitrogen, however, that does not move through the soil very fast. It's called Water Insoluble Nitrogen (WIN), and the fertilizer bag indicates what percentage of the total nitrogen is in this form. Water insoluble Nitrogen dissolves more slowly and stays in the plant root zone longer.
Lawns vary in their need for nitrogen. Maintaining an existing lawn requires less nitrogen than starting a new lawn. Maintenance applications should be split and applied over a few months, so there is less danger of leaching. A healthy root system can absorb most of the leaching nutrients.
The second number on the bag is phosphate (P205). New lawns benefit from a high relative level of phosphorus. This helps with seed germination and gets the roots off to a good start. Phosphorus is fairly stable and is held by the soil particles. There is a chemical balance of phosphorus in the soil, with some readily available and some held in reserve. But if erosion occurs, phosphorus can move with soil particles and contribute to pollution. Phosphorus also contributes to algae growth, although not as seriously as nitrogen.
The third ingredient on the bag, potash (K20), is a source of potassium. It contributes to the strength of the plant and helps the plant form carbohydrates. It does not contribute much to water pollution as potassium can bind to soil particles. However, if there is an erosion problem, this nutrient can move with the soil particles. A healthy plant cover greatly reduces soil erosion.
Soil Test
A soil test for your lawn can help you to make a wise fertilizer choice, which, in turn, can save money because you won't add nutrients your soil doesn't need. A soil test from Virginia Polytechnic Institute and State University provides information on pH, available phosphorus, calcium, and magnesium. It also provides nitrogen recommendations. You don't need to perform a soil test for your home lawn more often than every three to four years. Forms and sample boxes are available from your local Extension office.
Lawns grow best at a pH of 6.2 to 6.5. That is, the nutrients are most available to the grass plants in this pH range. Most soils in Virginia require lime to raise the pH to this desired level. The soil test gives specific recommendations on how much to apply to your particular area.
In our part of Virginia - where cool-season grasses (Kentucky bluegrass, tall fescue, perennial rye grass, creeping red fescue) are grown - fertilizer should be applied in the fall. September, October and November-December are best. Splitting the total yearly amount of fertilizer into three applications is recommended to minimize the potential for leaching.
The advantages of late fall fertilization are increased density, increased root growth, decreased spring mowing, improved fall to spring color, decreased weed problems, increased drought tolerance, and decreased summer disease. This helps the lawn green up faster in the spring and makes it more tolerant of heat and drought stress. When applying fertilizers, avoid getting it on paved surfaces; it can easily wash into storm drains, resulting in water pollution.
Your responsibility in using fertilizers safely and effectively results in a healthier lawn and better water quality of our surface and groundwater resources.
Joe Hunnings is the Virginia Cooperative Extension agent for agriculture in the Montgomery County Extension Office in Christiansburg. If you have questions, call him at 382-5790.|
by CNB