A basic understanding of fertilizers is a huge asset in sports turf management
December 9, 2011 By Mike Jiggens
Ratherâ€ˆthan killing weeds once they have appeared, sports turf managers
would be better off adopting measures to prevent them from occurring in
the first place, members of the Sports Turf Association were told in
September at the organization’s 24th annual field day in Oakville, Ont.
Dr. Eric Lyons, an associate professor with the department of plant agriculture at the University of Guelph, spoke to his audience about how to use fertilizers correctly to reduce the need for pesticides on sports fields.
The cosmetic pesticide ban has been in place in Ontario for three full seasons now, and has forced sports turf managers to reconsider how they approach best turf management practices.
“For most of our operations, it will get worse before it gets better,” Lyons said. “We need to change the way we approach it.”
Proper management is the means to prevent weeds from appearing on sports fields, he said, emphasizing the goal of achieving optimum growth or ensuring playing surfaces grow enough to recover from wear.
“If you have lots of wear, you need lots of growth. If you manage the use of the field, you can really reduce the wear. If you reduce the wear, you reduce the voids, and, if you reduce the voids, you reduce the weed encroachment.”
The correlation between grass cover and the booking of events on the fields must be realized, Lyons said.
“If not, we’re going to be in trouble.”
Once the amount of usage is better managed, sports turf managers will need to compete with the pest, which is accomplished through optimizing growth. Fertilizer is often misapplied after overseeding to repair worn areas, resulting in “a big waste of money.”
Lyons said when putting down seed, sports turf managers must realize the seedlings cannot handle high amounts of urea right away or burn will occcur.
Mowing is a key component in optimizing growth, he said.
“If you can’t mow it, don’t grow it. You don’t want to maximize growth, you want to optimize growth.”
If a sports turf manager is growing grass faster than he is able to keep up with mowing, he’s going to create more problems than if he just holds back on his fertility, Lyons said.
As a cultural practice, mowing most directly affects the grass plant. The individual assigned to mow the field is the one who will directly see its condition on a regular basis while the sports turf manager himself may seldom, if ever, see what is happening. The mower operator is the one who will monitor the turf’s growth on an ongoing basis and will make such other observations as turf burning from the misapplication of fertilizer.
Such observations must be directed toward the sports turf manager who can then better deal with booking to help ease the fields’ recovery from wear, Lyons said, adding it is imperative the mower operator regularly relays such information.
Sports fields are typically overseeded with perennial ryegrass because it is quick to germinate. But mower blades will generally dull faster when cutting perennial ryegrass compared to Kentucky bluegrass, thereby affecting mower maintenance.
Height of cut and mowing frequency are key toward affecting plant size.
“The lower you mow, the smaller the plant, the denser the plant…until you mow too low and then you get death.”
Frequent mowing encourages lateral growth, and mowing more often increases turf density. Dense turf wears better than thin turf.
“When you get out there and mow more frequently, you are actually increasing tiller density,” Lyons said.
When turfgrass is allowed to grow high, it shades out its neighbours. Neighbouring plants have the ability to discern whether they’re being shaded from another plant or by a building. Instead of growing new tillers or expanding out into divots or worn areas, the shaded plant will grow upward to compete with its neighbour for light. This causes the shaded plant to grow finer and finer leaves and fewer and fewer tillers, resulting in less wear tolerance.
“The higher the grass, the bigger the isue.”
Light quality is what inhibits the plant’s growth.
Turf density increases as mowing heights are reduced, but height of cut and growth rate will determine the frequency of mowing.
“If you’re mowing really low and have a high growth rate, you’re going to have to mow daily or every two days,” Lyons said.
Mowing low means having to mow more often if denser turf is the objective.
Lyons warned that if mowing isn’t done frequently enough, a significant cover of clippings will result and the turf beneath will be dying. Even if clippings are moved by mowing in the opposite direction, the yellow, weaker turf beneath will give weed seed a good chance to germinate.
Turf that is overfertilized will result in one having to “bale hay,” Lyons said, with the grass perhaps succumbing to the massive cover of clippings and opening the door to weed infestation.
Turf growth is stunted if mowing isn’t done frequently enough.
“The goal of fertilization or the goal of applying fertilizers is to provide enough mineral nutrients for optimal growth.”
That means that growth does not exceed the ability to mow it, yet the turf still grows fast enough to give it a chance to recover from the amount of wear is sustains.
“The more you wear it, the more growth you want,” Lyons said, adding it also means the more frequently it will need to be mowed.
Optimal growth is a balance between recovery and excessive growth. Nitrogen generally drives growth and recovery, but the amount needed and its rate will depend on the amount of wear, whether the field is sand or soil-based, and the particular municipality’s mowing schedule. The amount of nitrogen required will also depend on the municipality’s geographic location since growth rate is also influenced by the time of year and temperature. The amount of required nitrogen will therefore differ between Windsor and North Bay.
Lyons said a major concern is that many sports turf managers will put down a certain number of bags of fertilizer per field, but aren’t sure how that works out per 100 metres.
They may also be confused by fertilizer ratios, but it’s something they needn’t get hung up about, he added.
What they should know is that if their nitrogen requirements are higher than those of their phosphorus and potassium, they can use a straight nitrogen fertilizer since it’s how much phosphorus and potassium put down over the course of a year which is important. Sports turf managers can use a base fertilizer containing phosphorus and potassium that is put down twice a year, and straight nitrogen can be used the remainder of the time.
Urea is the most common type of fertilizer applied. It is broken down into ammonium which can volatilize as ammonia and escape. It can be transferred into nitrate which can leach into the groundwater or it can be taken up by the plant which it has to be back-converted into ammonia and then turned into amino acids and proteins.
Since the coming of synthetic fertilizers, there have been great advances in fertilization. With urea, it is put down, there is a flush of growth and lots of volatilization and leaching “and very little of what you put down is taken up by the plant.”
Controlled and slow-release fertilizers produce steadier growth, and more of the nitrogen put down gets taken up by the plant.
“That means you can actually apply less per season,” Lyons said.
Once it’s down, it’s down, he said, and even the slightest overlap will produce a stripe lasting for two or three months. With urea, it’s gone in three to four weeks.
Most fertilizers today are a combination of readily-available and slower controlled-release nitrogen, producing fairly quick greenup and steady growth throughout the season. With many of these fertilizers, the size of the prill determines how quickly it releases.
Lyons said if a sports turf manager is using a water-release mechanism fertilizer, and there is an extended period of drought, there’s won’t be much release unless the fields are irrigated. Some managers may have put down a second application during the past summer’s drought period and, once the drought was over and rain returned, two separate applications were released.
He said it’s important for sports turf managers to understand how their fertilizers release, which allows them to better adapt their fertility programs for the future, permitting them to keep up with mowing.
Sulfur-coated urea is a fairly inexpensive coating, Lyons said, and is perhaps the most common slow-release fertilizer available today. Typically, it is 30 to 40 per cent nitrogen whose coating is dissolved by water. A particularly thick coating will inhibit its release.
Polymer coatings typically control release by the diffusion of water across a plastic membrane. Because it’s diffusion, it’s temperature-based. Depending on the temperature, water passes through the coating and most will release rapidly above 21 degrees Celsius. Some coatings may be susceptible to mechanical damage but not to the same extent as sulfur-coated urea.
Other fertilizer types include cold water-insoluble nitrogen, whose slow-release ability depends on how much is insoluble, and methylene urea in which anywhere from 25 to 60 per cent of the nitogren can be cold water-soluble. Methylene urea are carbon chains attached to nitrogen in which the size of the chain controls the release. The longer the chain, the slower the release. Microbes eat the carbon and then release the nitrogen.
Burning can occur with methylene urea if too high a rate is used.
Formaldehyde ureas have longer chains. Less than 15 per cent of the nitrogen is unreacted and provides a more consistent slow release.
“For some people it’s too slow,”â€ˆLyons said, adding many prefer the methylene or sulfur-coated ureas.
He said it’s important to understand how the various fertilizers release so that applications can be timed accordingly. Again, the mower operator is the one who will see the effects of fertilizer more than anyone else, “whether they’re baling hay or barely cutting.”
Lyons warned his audience to exercise caution with regard to organic fertilizers, saying it’s difficult to grow turf with them. Organic fertilizers include manures and animal byproducts, kelp, bone meal, corn gluten and leaf litter.
“Just because it’s organic doesn’t mean it won’t burn. It doesn’t mean it’s not readily available.”
Slow-release organics depend on microbial activity and temperature, and water must be present. The mindset behind organic fertilizers is that carbon is being put into the soil, thereby stimulating microbial activity and contributing toward a healthier system. Fewer pests will be present and less pesticide will be required.
Lyons said that’s good for agriculture, but less soil carbon is preferred in turf. Carbon is controlled by introducing oxygen through aeration.
The percentage of nitrogen in organic fertilizer is usually less than 12 per cent, requiring more of it to be put down. It can also be expensive if trucked from afar, such as one of the more popular organic fertilizers which is shipped from northern California.
A local product may have the best cost and best environmental benefits, but it’s usually inconsitent, Lyons said. There may be application issues which arise from putting down so much material that it acts like excessive grass clippings and smothers the grass.
All fertilizers have both advantages and disadvantages, he said.
“Without proper application and the person in the field paying attention to what’s happening with growth rates, it really doesn’t matter.”
It’s also important to realize that sand-based fields can’t be fertilized in the same way as soil-based fields, Lyons said. They don’t have as much organic matter in them and don’t have the same ability to hold nitrogen.
“If you have a sand-based field and the guy booking isn’t paying attention and, all of a sudden they book five hours a night for two weeks, you can kill the field in less than a week because it’s a sand-based field. A soil-based field may be able to survive that. A sand-based field has no chance.”
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