It's encouraging that more and more frequently the terms "ecosystem" and "ecosystem management" are being heard among those serving the turf industry. But, like many such terms, a clear sense of their meaning and implications remain vague.
Put simply, an ecosystem is an operational, self-sustaining system that includes the physical environment and all the biological components in a natural community. In nature, ecosystems occur as a stable endpoint, the climax community. Examples of climax communities, termed biomes, include grasslands, forests and woodlands, among others.
What the turf manager must recognize is that turf, whether on a lawn or a golf course, is an imposed climax community. Unlike natural biomes, turf often lacks the functional and environmental support that precedes a natural climax community. The task for the ecosystem manager is to provide this support with appropriate soil and water management, appropriate fertilizers and growth regulators, and, appropriate weed, insect and disease controls.
The ecosystem of typical turf soils is housed in an environment consisting of:
- 40--50% mineral matter
- 50% +/- pore space, which is occupied by water and air
- 3-6% organic matter, and,
- <1% living organisms
But these proportions should not mislead you! There are constant dynamic forces driving endless interactions among these constituents.
What drives an ecosystem?
Soil cation exchange
- Cation exchange capacity (CEC) is the measure whereby negatively charged clay minerals and organic matter remove positively charged cations, i.e. ammonium, potassium, calcium and magnesium, from the soil solution.
- Cation exchange capacity provides a reservoir of plant nutrients to replenish those removed from the soil water by plant uptake.
- Cation exchange is also a buffer for soil pH, and, the higher the cation exchange capacity the more it takes to changepH.
The microbial community
The microbial community
Its action is most immediately reflected in the carbon to nitrogen (C:N) ratio. A narrow C:N ratio in the organic matter, fertilizers and amendments will enhance:
- Rate of decomposition
- Resultant release or mineralization of nitrogen
- Nitrogen availability for plant needs.
Conversely, a wide C:N ratio may immobilize and sequester nitrogen in the tissues of the microbial decomposers leaving little available to satisfy plant needs. Generally, microbes have a cellular C:N ratio of approximately 10:1. Organic matter with C:N ratios significantly higher than 10:1 will require further decomposition, resulting in nitrogen immobilization until microbial needs are satisfied. Thus the C:N ratio becomes a critical criterion when considering the addition of organic fertilizers and amendments.
Disruption of the ecosystem
Turf management practices, by their nature, disturb the ecosystem through mowing, irrigation, fertilization, cultivation, aerification and topdressing.
The application of amendments, growth regulators, pesticides, and herbicide applications also disturb the ecosystem; even modified soils such as USGA sand, have a profound impact on the ecosystem. These disruptions of the turf ecosystem result in a new equilibrium, a "synthetic" and potentially fragile one.
This "new" ecosystem may be evidenced by:
- Reduced overall blade area
- Poor turf coverage
- Poor root extension and density
- Reduced ability for mineral uptake
- Rapid thatch development
- Inefficient water use
These conditions can cause the development of an anaerobic soil environment, the accumulation of residual soil organic matter, and anaerobic black layers. As a result, root systems are reduced and soil microbial populations are stressed, leading to increased disease, insect and nematode activities. Classically, these symptoms have been viewed as management problems to be resolved only by increased chemical usage and ration/dethatching events. Fortunately, our recognition has now matured to view problem solving, not in “quick-fix” terms, but in a systems approach designed to restore and sustain a vital ecosystem. The dilemma now facing the turf manager is essentially: how to restore the ecosystem?
Restoring the ecosystem
In principal, an ecosystem can be restored by:
- Strengthening and maintaining existing microbial populations, the biological drivers of all soil transformations;
- Adopting a more "organic" mode of fertility with appropriate materials of narrow C:N ratio.
- These practices can reduce or eliminate nitrate leaching into ground and surface waters.
- They will, by competitive exclusion, reduce disease incidence with a subsequent reduction in fungicide and other pesticide use.
- The degradation rate of residual organic matter including thatch/mat will be increased.
- Mineralization and release of mineral nutrients will be enhanced
- Cation exchange capacity will increase
- There will be an increase in rhizosphere and phyllosphere interactions.
Biological transformations can be further enhanced by reassessing the irrigation program, and, developing a strong aeration/verticutting program. The turf manager will, of course, need to identify the specific products that will sustain the restored ecosystem. Here the criteria for choice should include the presence of a product roster integrated into a systems approach; one that may combine plant nutrition, soil amendment and disease control sustained over the season. The products themselves, whenever possible, should be organic in nature and capable of sustaining a vigorous microbial population compatible with ecosystem demands.
In summary, the soil ecosystem is a dynamic, living entity in which mineral matter, soil atmosphere, water, organic matter and living organisms are in constant interaction. The driving force in soil transformations is the soil microbial community. Soil organic matter is the matrix within which the major transformations occur.
Restoring and maintaining the ecosystem begins with the application of the appropriate fertilizers and amendments.
About the author
Haim B. Gunner,Ph.D., is an Emeritus Professor at the University of Massachusetts and chief scientist at LidoChem Inc.