No matter how often you add gas to your car, it’ll always run out and need more to operate. To a certain extent, bermudagrass is like a car: If you want it to perform, you have to feed it – sometimes a little or sometimes a lot, depending on what you want it to do. If you’re after vigorous growth, then you must provide more fertility. If you’re thinking about less vs. more, it’s best to consider that on an annual perspective instead of each fertilizer application.
As illustrated by Figure 1, warm-season grasses are in most need of nutrition during the summer months following spring green-up. Warm-season grasses can be sluggish coming out of winter dormancy, especially with wet, cool and cloudy spring weather. Applying nitrogen (N) too early can deplete root nutrition levels, leaving the plants vulnerable to unpredictable spring growing conditions.
In northern areas, warm spring weather can encourage growth only to be followed by frosts in repeated cycles, critically depleting carbohydrate reserves and damaging shoots and roots. These conditions provide an opportunity to apply phosphorus to aid in green up and possible regrowth of roots.
Knowing the soil
Fertility programs should begin with consideration of the current soil nutrient status as well as thought-out goals and outcomes for the turf. Up front, it’s wise to consult past records and test at the same time as was done previously.
Comparisons from year to year are most accurate when tests are conducted in the same month. From a timing standpoint, relating test results from one season to the next is problematic in that they’re often misleading due to biological occurrences that occur naturally throughout the year. For example, as soil temperatures rise, the microbial population of the soil increases as well, affecting nutrient availability and the potential for misrepresentation of the organic matter content and concentration levels of various nutrients.
The previous performance of the turf should influence the specific areas to be tested. The ones that are viewed to be consistent in growth and appearance should be tested separately from those with random patterns.
Once areas are identified for sampling, cores should be removed 5 to 6 inches deep. Any vegetative tissues – crowns, blades, stolons, rhizomes – should be separated from the sample and discarded along with the thatch. When sampling, concentrate on the soil particles in the 2- to 5-inch level of the soil profile.
When it comes to soil sampling, both the “law of diminishing returns” and “the more the better” apply; as such, an even dozen is a good number to shoot for per section of sampled turf. Mix these together in a plastic bucket and send them to a reputable soil-testing laboratory. Throughout the entire process, keep consistency in mind in that changes in sample depth, time of year, lab used and overall testing methods can distort the results and their usefulness.
As soil test results are interpreted, specific calculations for each nutrient and other soil test features can differ. Generally, soil tests for phosphorous and to a lesser extent potassium are usually more reliable than for nitrogen, in that they are more stable in the soil from year to year. Because nitrogen is a transient and mobile nutrient, test results should be thought of as a “one-time” or “today only” result rather than an etched in stone fact.
Season to season
Out of dormancy, applications of a half-pound to 1 pound of nitrogen per 1,000 square feet are often recommended once turf is completely green. If soil test results are not available, a slow-release, complete N-P-K turf fertilizer in a 4-1-2 ratio is a reasonable beginning point for the season.
However, if results are available, more precise applications may be made. As the various nutrient categories are being considered, the readings for organic matter and pH/liming need should be take into account as well. Especially following hollow tine aerification, adjustments via topdressing are timely as the season begins.
Over the summer months, recommendations vary depending on the desired growth rate and the traffic expected by golfers. Depending on the intensity of each, applications of a half pound to 1 pound of N every four to six weeks are generally called for in early, mid and late summer. As the effects of play, weather and growth rate are monitored, adjustments can be made to maximize performance.
Consistency of applications at regular intervals with quick release sources of N or well-timed applications of slow-release sources will help avoid peak-and-valley feeding of the turf. This can in turn reduce to potential for summer stress and overdevelopment of thatch (See Figure 2).
To aid in selecting nitrogen (N) fertilizer carriers, Figure 3 provides a comparison of various types of N carriers available, their N release characteristics and their estimated N release residuals.
In late fall, a traditional approach has been to reduce the frequency and intensity of applications in an effort to glide into early winter without much in the way of hearty plant growth that would likely be damaged as cold temperatures begin their influences.
It’s difficult to argue with this tried-and-true methodology, however, research at several land-grant universities has indicated that applications of soluble N in mid-fall had the effects of producing enhanced fall and spring color of bermuda turf without causing undesirable outcomes of increased potential for winterkill. The studies also indicated that slow-release N sources failed to produce the same responses.
In light of these discoveries, the application of low to moderate rates (0.2 to 0.4 pound N/1,000 square feet) of quick release N approximately two weeks before the onset of dormancy will provide needed nutrients for root and rhizome growth without stimulating excessive top growth. The lower, more quickly available formulations are in keeping with the questioning of the eventual fate of the N previously recommended, in either the slowly or quickly available forms.
The basic question is: If a large amount was applied in the fall and a small amount was recovered in the spring, then what happened to the remainder? Really, only two possibilities exist – it was used by the plant and it left the turf and moved to the atmosphere, or it leached into groundwater, both undesirable outcomes.
The balance with this approach is applying just enough that will be immediately absorbed and utilized in the plant, but not more than is needed, as it’s likely to be wasted or lost from the site.