With 46 years of industry experience, and having written numerous articles for many trade publications, I thought hard on what I could say that would benefit GCI readers.
Boiling down what I believe are the most important lessons learned over nearly a half century, I believe learning how to manage stress is one of the more important issues.
I am not taking about my stress, but the stresses golf course turf must contend with throughout the season. These are important issues, especially for plant health. I have been preaching plant health now my entire career, long before it even became a buzz word in our profession. In simple terms, the less stress, the healthier the turfgrass.
Here are the three turfgrass stresses you must be aware of:
- Water use and stress
- Stress created by poor root growth
- Nutritional stress
Water Use and stress
To discuss water use, we must first discuss the water cycle. Plants take in water through the roots and the absorbed nutrients from the soil are carried into the plant by the water. The stomata of the leaf regulate water movement in the plant and by extension also the nutrients. The stomata of the leaf are the controlling factor and regulate the system. Water is evaporated by the stomata which reduces the pressure in the vascular system and brings more water and nutrients into the plant and into the leaf where it is converted into carbohydrates by photosynthesis for plant growth and storage in the root system. The passage of water from one state to another causes a drop-in temperature. Transforming water into vapor is how plants cool themselves when it’s hot. This process is directly related to solar radiation and is called transpiration.
Thermal stress happens when the temperature of the plant at the surface is about 10 degrees greater than ambient temperature. It causes the stomata to close to protect the plant. As golf course superintendents, we use that law of passage of water from one state to another causing a drop in temperature. We syringe the greens to cool them off as the water evaporating from the syringe of the turf also cools the turf just like an evaporative cooler works. Thermal stress is also often called temporary stress or summer stress and as long as there is available water in the soil, this stress is temporary.
If there is not enough water in the soil to take care of the plant’s needs, we then have hydric stress, which if water is not added to the soil causes death of the plant. A little hydric stress at times can favor root development
Water also evaporates through the surface of the ground and that is called evaporation. The sum of water losses attributable to evaporation through the surface of the ground and transpiration from plant tissue is evapotranspiration (ET).
The sum of the ETs since the last time it rained or you irrigated is the maximum amount your turf needs. Regardless of how much water is present in the soil, the volume that can evaporate in a day is limited by the amount of energy that the sun can provide.
The stress of poor root growth
Root function is absorption of water and nutrients, a major factor in stress tolerance. Roots are also a contributor of organic matter to the soil nutrient pool.
Roots need energy and they are not photosynthetic. Therefore, they depend on the photosynthetic energy captured by the leaves and shoots. The amount of energy captured depends on its leaf surface, the duration of light and the extent by which production is decreased by stresses such as heat.
Approximately 50 percent of carbohydrates produced in photosynthesis are stored in the root and 30 to 80 percent of carbohydrates in the root are excreted from the plant to the soil. These metabolites provide an energy source for the microorganisms. The micro community uses this food source and in return breaks down nutrients in the soil for the roots to absorb. It is a symbiotic relationship.
Increased populations and diversity of soil microorganism increase nutrient availability, immobilize nitrogen in root zone, reduce nitrate leaching, conserve nutrients in the soils biological fraction, improve organic material breakdown and nutrient recycling, and enhance the formation of soil structure which improves aeration and draining.
Because the roots are responsible for the soil organic matter in the form of exudates needed for the microorganisms to flourish and provide the balance needed in the soil, then anything we can do to manage for maximum root growth becomes very important.
We can promote maximum net carbohydrate production through optimum leaf area. As my career moved along, the height of cut came down and the older turfgrasses would not tolerate the low height of cuts. We now have better varieties of both bentgrasses and Bermudagrasses which provide more leaf area at low mowing heights. We must also keep mowers very sharp so we do not destroy what leaf tissue we have. We must also prevent wear damage and loss of leaf to diseases and insects. As height of cut has come down, root growth has come up. At current mowing heights at or below 1/8ths of-an-inch there is simply not enough photosynthesis to make enough carbohydrates to go around and root growth suffers.
Optimum chlorophyll content in the leaf becomes important for carbohydrate production at low mowing heights, and we must avoid N, Fe, Mn, Mg, P and S deficiencies. We also must promote good light conditions (pruning) while avoiding prolonged drought stress (stomata closed-CO2) and overwatering. We also must correct poor soil chemical conditions such as acid (lime), alkaline (S, sulfuric acid, acid-forming N carriers), infertile soil and saline conditions (gypsum, S, drainage).
Nutritional stress occurs when the plant is not getting the proper nutrients from the soil and there are many reasons that can happen because roots at times and under certain conditions are limited in their uptake of nutrients. For uptake to occur, the soil needs proper moisture, proper temperatures, proper pH, a good microbial community and other biological factors. Uptake of nutrients from the soil is very much a biological process subject to environmental conditions. All available nutrients must be soluble in water as that is how it is transported into the plant.
I learned along the way that foliar feeding is a good way to relieve nutritional stress, and I spent the last 20 years of my career teaching that principal. It boils down to basic agronomics. I am first and foremost an agronomist. One of the first rules I learned in school was titled “Agronomic Law of Minimum,” which says there are 13 essential elements required for plant growth other than C, H and O, and each one needs to be at optimum levels for optimum growth and health. Growth and health will only reach the lowest optimum level present for any nutrient, and no element may substitute for any other element.
Remember those elements that enhance chlorophyll production during photosynthesis are N, P, S, Mn, Mg, Zn and Fe, and good chlorophyll equals good carbohydrate production at any given height of cut, which gives us better root growth. Foliar feeding is a good way to make sure none of those nutrients are missing. Foliar feeding is a chemical and physical process and not a biological process, and the plants utilize the nutrients they obtain the same way from soil or foliar feeding.
With foliar feeding, we get better response with a poor root system. Once a soil applied nutrient is below the roots, it is no longer available to the plant. Better response without optimum soil pH and availability depends on each nutrient because all react to pH different. Good results with plants under stress and I believe a low dose of a good foliar nutrient will help alleviate most stress under most conditions. Foliar feeding is simply the best spoon feeding program for turf.
“In simple terms, the less stress, the healthier the turfgrass.”
Foliar nutrition is an effective method of providing a steady flow of nutrients to the turfgrass. The down side of foliar nutrition is that it does not provide a usable nutrient pool in the soil for the plants to use, so I believe it needs to be used in combination with other traditional types of root-uptake fertilizers. It is another management tool for progressive golf course superintendents who want to achieve better control of nutrition and growth.
Plant growth elicitors are among the good foliar products. I call those value-added products. Elicitors are molecules that stimulate plant defense mechanisms, and promote plant health or wellness. This family of substances may have other beneficial effects on plants such as improving the final quality of the product and water efficiency, and increasing plant biomass and the resistance to abiotic stress, and/or reducing the effects of abiotic stress.
The abundance of minors, kelp extract from Ascophyllum nodosum, silica in small amounts, phosphites, natural plant growth regulators, hormones and vitamins are other value-added products.
Some other elicitors that have been identified include phytoalexins, specific amines or amino acids, carboxylic acids, phosphites, and other phosphonates, silicon, glycoproteins and oligosaccharides, peptides, jasmonic acid, salicylic acid, arachidonic acid and sugar analogs. Many of these are also lumped under the term phytohormones, phytoprotectents or biostimulants. Some may refer to these as “snake oil,” but science is beginning to show their value more and more.
There are many new companies bringing customers cutting edge products manufactured with a high degree of purity and quality that provide plant health and wellness. Companies with good science behind their products and use university independent valid test results to show the efficacy of their products. These products may help avoid plant stress and bring us better plant health.
Gary Grigg, CGCS, MG, is the vice president and agronomist for Grigg Brothers and past GCSAA President.