Lawns, Water and Nitrogen
When you buy and apply fertilizer to your lawn, you are feeding the grass plants with a combination of three plant nutrients. One of those nutrients, nitrogen, encourages green plant growth and is one of the key elements of plant life. Most of the nitrogen in the soil underneath your lawn is tied up in the organic matter. Through Mother Nature's soil nitrogen system, this nitrogen is continually being transformed and used by plants.
Nitrogen, usually extracted from the air, is combined with phosphorus and potassium to produce manufactured fertilizer products. The nitrogen in a lawn fertilizer supplements the natural nitrogen from the soil's organic matter, and together, these plant nutrients provide you with a vigorous green lawn.
Fertilizer ratios
The ratio of three numbers on a fertilizer product label tells you the amount of nitrogen-phosphorus-potassium in the product by weight. The average nitrogen-phosphorus-potassium contained in a blade of grass is about 4-1-2. A lawn fertilizer in the ratio of 24-6-12 is almost an exact replacement of the nutrients that the plant demands from the soil.
Fertilizing your lawn
Early in the growing season, quickly growing grass plants need more nitrogen than is available through the supplies held by the soil. Granular fertilizers formulated specifically for lawns also offer the advantage of slow-release nitrogen, making the nitrogen available to the plant at a consistent rate for a period of six to eight weeks. Fertilizers designed for agricultural use do not release the nitrogen at a controlled rate and may injure your grass plants.
As grass grows, new green shoots replace old shoots, which die and create a layer of thatch on the surface of the soil. As these grass clippings decay, they will also become part of the thatch layer. A healthy lawn, cut at the recommended height of 2" to 3", will contain a layer of thatch about 3/4" deep. Grass that is properly fertilized will naturally maintain the proper thatch layer, and will be able to fight off diseases such as brown patch and powdery mildew Healthy grass plants will be better able to compete against weeds.
Fertilizer and surface water
Your lawn contains 1.5 to 5 grass plants per square inch. When rain or water from a sprinkler falls on your lawn, all of these plants act as sponges and dams, trapping and holding the water in the thatch layer and the roots. Little or no water will escape from your lawn during the average rainfall.
When you apply fertilizer to your lawn, it falls into the thatch layer, and is absorbed by the soil's organic matter. Even in a very heavy rain, very little if any nitrogen would be dislodged from the soil and carried away in water washing off the surface of the lawn.
Fertilizer and groundwater
Growing grass uses over 70 per cent of the water that reaches it from rainfall and sprinklers. The remaining water that moves deep into the soil may become groundwater. The nitrogen applied in lawn fertilizer (when applied at the recommended rate) is absorbed and held by the soil's organic matter and is taken up by plants. It does not travel with the groundwater as it moves through the soil.
Keys to safety and success
- Apply fertilizer according to label instructions.
- Fertilizer was formulated to be spread onto the living surface of your lawn. Sweep any fertilizer that lands on the sidewalk or driveway back onto the lawn.
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