The sports turf management paradox is to create a safe, beautiful and playable surface while staying on budget and being sustainable. As many readers know this is easier said than done; sports turf managers face comical constraints and an endless stream of demands. We’ve all heard some form of “It’s just mowing grass,” right?
Do these sound familiar?
- The field needs to be playable even though it has rained for 7 days.
- Your task list requires twice as many people as you have.
- You need to find a miracle fertilizer to keep grass healthy at half cost.
- Your organization wants to leverage perception by not negatively impacting the environment.
- Water consumption needs to be reduced but the grass better be green even when it is 100 degrees with no rain for months.
You should be doing more for your turfgrass to thrive, not just survive. But, honestly, how?
Work the problem
We suggest three strategies: see the whole plant; look for parallels; and reduce the complexity to essentials.
When we think landscapes, most of us think about shoots. The roots (~50% of the plant) and the complex soil environment they grow in are often ignored. We should give more than a passing thought to “dirt” and its vast population of organisms.
In terms of parallels, compare turfgrass to humans. Both are intricate organisms . . . and sometimes difficult to repair. On the other hand, providing suitable nutrition and care is cheap in comparison—prevention is the key. Most of us understand this for ourselves, but don’t apply it to turfgrass.
Finally, we shouldn’t let complexity confuse us (or be used against us to sell us high $ snake oils). Growing turfgrass can be reduced to a simple set of variables as we blend these strategies to be better Grass Masters.
What are the variables?
The system is complex, but to simplify management, we need to understand plant needs. How can we grow healthy turfgrass in a water bucket? By supplying its needs artificially. Growing turfgrass hydroponically in a growth chamber is tricky; you must ensure everything is provided and maintained in balance. Light is provided electronically. The pH is carefully buffered. Pests are rarely a problem due to isolation, but sometimes fungicides are needed. Nutrients are carefully balanced. The normal atmospheric air provides ample carbon dioxide and oxygen. Although this is adequate for shoots, the roots need additional air bubbled into the rooting solution.
What does hydroponically grown turf have to do with anything in the real world?
We can draw parallels to aid our understanding and management. It demonstrates that we know everything turfgrass needs, not only to survive, but to thrive. One thing we’ve learned from hydroponics is the effect of nutrient balance. Countless studies show what happens when nutrients are deficient and also when they are excessive. And, we’ve learned the importance of oxygen. The roots can be literally bathed in water as long as there is oxygen present. Even though shoots are surrounded by ubiquitous oxygen and some oxygen-containing compounds are is translocated to the roots, it isn’t enough and air has to be provided for in the rootzone.
Where should we focus? Our outcome control comes down to a smaller subset of variables.
Variables we generally don’t have to worry about include:
- The sun provides the light for us as long as we aren’t too shaded (i.e. no light bulbs necessary most of the time).
- The air provides carbon dioxide and oxygen to the shoots.
- The soil provides a growing medium, anchor, and a nutrient store
- The basic laws of biology, chemistry and physics often take care of our plants.
If everything necessary for life is provided, biology thrives regardless of complexity. If a plant is already healthy, it’s likely to fight off potential pathogens, such as pythium or brown patch. If it’s well established, weeds can’t compete. If roots are encouraged to grow deeply early in the season, the turfgrass will thrive even when it’s blazing hot in August with no rain. The turfgrass will hold up better under the wear and tear when the coach insists on practicing in the exact same spot every day. All because the soil is healthy.
The soil is one thing that we do need to worry about and there are specific aspects to focus on. Healthy soil = healthy roots = healthy grass = healthy, and happy, turfgrass manager. Well . . . mostly . . .
What soil variables matter the most? Optimal levels of mineral nutrients (nitrogen, potassium, etc.), and balancing non-mineral nutrients (water and oxygen).
Optimizing mineral nutrition
Plants require 15 essential mineral nutrients and benefit from others. However, the most important is nitrogen—the rest aren’t even in the same league. In our experience, most turfgrass is receiving deficient or excess amounts of nitrogen. And in the sports turf world nitrogen is usually excessive. It is like an illicit drug . . . sure it gives a short-term pleasing look, but the long-term impacts are unhealthy roots and increased disease and insect pressure.
Soil, water, and plant tissue testing can fine-tune a nitrogen fertilization program by identifying excesses and deficiencies. However, unlike most nutrients, soil testing poorly determines base application rates because nitrogen is so transient in the system.
Ideally, nitrogen is spoon fed at 2.5-3.5 lb. N per 1000 sq. ft. throughout the growing season because it is so easily lost below the shallow turfgrass rootzone or to the atmosphere. Less is needed if the irrigation water source has nitrogen in it, which is surprisingly common.
Uniform application is key (compared to applications to species with larger root systems which can effectively use large fertilizer particles every few inches). Unlike other plants, the rooting cylinder for an individual turfgrass plant is tiny. Thus, frequent foliar sprays or injection into the irrigation system of urea ammonium nitrate (28-0-0 to 32-0-0) or similar is ideal. If applying with the irrigation, realize that sprinkler patterns are never uniform, resulting in higher nitrogen in areas receiving more water.
For soils with low nutrient holding capacity (i.e., sandy and less organic matter) more frequent applications are needed. Some turfgrass grown in sand gets an application with every irrigation. Otherwise, monthly applications suffice.
Although this is the ideal, this approach is costly and time consuming.
Another option is using control or slow release fertilizers at higher rates per application. These fertilizers are costly, but generally labor savings of fewer applications offset this. Our research reveals a minimum of two applications is needed for results to be almost identical to constant spoon-feeding. Note: carefully select these products and use only those scientifically and independently vetted. Despite claims, many are ineffective, with their effect largely gone within a few weeks.
We recommend applying the following rate in early spring and double this rate in early fall. Note: the high rate in the fall has proven to be the most effective application to help survive dormancy and to provide healthier roots into the next summer.
- 5 lb./1000 sq. ft. ammonium sulfate (21-0-0-24S) or 0.6 lb./1000 sq. ft. urea (46-0-0) if your sulfur is high in the water/soil
- 5 lb./1000 sq. ft. polymer coated urea (43-0-0) or similar controlled/slow release nitrogen
This equals 1 lb.-N/1000 sq. ft. in spring and 2 lb.-N/1000 sq. ft. in the fall and about 0.3 lb.-S/1000 sq. ft. of the sulfur nutrient, which is likely enough for most situations. Sandy, low organic matter soils may require up to 50% more of these fertilizers.
Other nutrients are generally easier to manage because soil holds them in supply to plants using principles of equilibrium chemistry. It is rare to find deficiencies in turfgrass of anything other than nitrogen phosphorus, potassium, sulfur, and, in cases of older varieties, iron. Sounds complex? Well, we recommend soil testing, especially for phosphorus and potassium, to insure adequate, but not excessive, levels. Remember, too much of a good thing is toxicity, which is very common.
Take a proper sample and submit to a trusted lab. Generally the lab can provide guidelines for interpretation based on the methods they used and the scientific calibration of those tests. We emphasize to not fertilize with nutrients that are already adequate in the soil; at best it is a waste of time and money and at worse can cause toxicity and legal liabilities due to environmental hazards.
Balancing water and oxygen
This is a thorny problem. Plant roots need water and oxygen, and a toxic gas escape pathway from soil. Unfortunately, soil water saturation pushes oxygen out and eventually traps toxic gases. Plants can grow submerged in water as long as they have oxygen. In a well-developed soil there is a balance of water holding micropores and air filled macropores. Unfortunately, frequently overwatered and heavily trafficked sports fields have compacted pores, resulting in more water and less air.
Unlike nutrition, we don’t have simple reliable aeration tests. Rather, we assess soil moisture through hand probing and sensors. Also, smell your soil. Yes, smell is an excellent detector. Soil cores will have a “swamp” gas smell when they are lacking oxygen.
How do we prevent oxygen deficiency? We start with drought tolerant varieties/species, proper mowing heights, nutrient (especially nitrogen) management, intentionally moisture stressing the grass in the spring, and other best management practices to foster deep root development. Drying the soil down between irrigation and then refilling the profile with water to rooting depth is essential. And, managing the macropore content of the soil is another key through traffic management, frequent aeration and topdressing. Some soils (such as ASTM spec sand rootzones) require rare aeration; others require it frequently in proportion to traffic rates. Still others, which are prone to compaction (such as sandy loams), require near constant aeration.
Most of us are applying too much water and fertilizer and not supplying enough oxygen to roots. Great soil doesn’t solve all your problems. And your bosses may not understand or appreciate your ninja-like Grass Master skills. But that’s the difference between a layman and a master craftsman, who sees beneath the surface, focusing on what is not seen.
Bryan G. Hopkins, PhD, is a Certified Professional Soil Scientist and a professor in the Plant and Wildlife Sciences Department at BYU in Provo, UT. Tyler J. Hopkins is now with SciScapes in Provo.