With ample rain and warmer weather many of us have been working to enhance the quality of our lawns. In many cases this means providing adequate plant nutrients to maintain a high quality lawn. To help with that, AgriLife Extension in Nueces County has partnered with the City of Corpus Christi to offer free soil testing in early spring over the last 4 years. As a result, over 800 urban soil samples have been submitted to through the program and some basic trends can be observed.
We often generalize our suggested lawn care practices and often assume that what is good for our neighbor is good for us as well. For example, our predominantly clay soils are generally assumed to be relatively high in two of the three main macro-nutrients we typically fertilize for; phosphorus and potassium. However, results of the campaign suggest that 27% of the samples submitted required additional phosphorus to insure a healthy lawn. An application of some potassium was recommended 7% of the time. Also, we generally assume that most of our soils will need additional nitrogen to maintain a high quality lawn and yet 35% of the samples submitted suggested that no additional nitrogen be applied. The most common soils fertility suggestion was 0.9lb of nitrogen per 1000 square feet of lawn; however this suggestion was only made in 7% of the submitted samples. These results highlight the variability of fertility levels in our soils and the value of soil testing.
Excess nutrients in our soils have the potential to runoff, enter storm water, and become directly discharged into our area receiving waters such as Corpus Christi Bay. In fact, it has been estimated that 45% of rain on our lawns is lost to surface water runoff. Along with the water coming off our lawns we lose around 32 lbs of soil per 1,000 square feet of lawn. This soil lose comes from our nutrient rich topsoil layer, and once it has reached our receiving waters can become a pollutant.
The over-enrichment of water with nutrients is called eutrophication. This will cause rapid growth of algae and other plant life. When the plants die and start to decompose, bacteria begin to use up all of the oxygen in the water. The oxygen level can become so low that many types of fish, insects and other animals can no longer survive.
From a healthy lawn stand point, excessive phosphorus build-up in the soil can lead to deficiencies in iron and zinc. Deficiencies of these nutrients will cause yellowing of turf grass. High levels of nitrogen can also promote fungal problems like take-all patch in St. Augustine lawns. For these reasons, soil testing and applying recommended amounts of fertilizer are the best way to protect the environment and maintain a healthy lawn.
In addition to managing soil nutrients, homeowners can also improve their lawns quality through regular mowing. Ideally we should remove no more than 1/3 of the leaf during any mowing and have our mower set at a height of 2 ½ to 3 inches. Frequent mowing at a lower height produces higher quality turf. Not only does it help the turf have a denser fuller look, but it also helps control weeds as well.
While generalizing fertility suggestions are not ideal for the reasons mentioned above; in the absences of a soil test recommendation homeowners should use a completer fertilizer with a 3-1-2 ratio of ratio of nitrogen, phosphorus and potassium like 15-5-10 for their initial spring application. About 1 pound of nitrogen per 1,000 square feet should be applied.
To determine how much of a fertilizer product to apply you divide the pounds of nitrogen desired per 1,000 square feet by the percentage of nitrogen in that product. So with a 15-5-10 fertilizer to put out 1 lb of nitrogen you would divide 1 / 0.15= 6.6 lb of 15-5-10 fertilizer per 1,000 square feet. Following the initial application homeowners may choose to apply 1 pound of soluble nitrogen per 1,000 square feet every 8 to 10 weeks until 4 to 6 weeks prior to first expected frost using a nitrogen-only fertilizer such as 21-0-0.