What is the best way to gauge the frequency and type of de-thatching operations needed for any one situation?
Can the amount of thatch/organic matter be measured and monitored as well as setting optimum target values to work to, thus avoiding any potential secondary problems due to thatch getting out of control?
Is it possible to monitor thatch/organic matter to tell if levels have increased and/or reduced in any one year?
The answers will be provided to all of these questions if you are using STRI's organic matter testing service as part of your ongoing management programme.
Organic matter - the pros and cons
Organic material is an essential part of the soil profile within all golf greens. However, it can deliver either positive or negative properties depending upon how much there is, where it is, and how it is managed. We commonly know organic material near to the surface, hopefully only contained within the first 25 mm or less, as thatch.
Thatch is best described as the amount of live, dead and decaying organic residue between the base of the plant and the green's upper soil rootzone layer. It is often sponge-like in texture and should be porous as well as ameliorated with top dressing materials. Its nature controls many key physical aspects of golf green performance, not to mention management requirements. Beneath the thatch will be more organic material forming part of the rootzone structure/texture.
On golf greens, we rely partially on thatch to produce the positive qualities of surface resiliency for ball-to-surface interactions. It is also the combination of thatch with other important criteria, such as sward cover and soil type/condition, which often determine many performance traits.
Other performance aspects related to greens' surfaces and thatch properties are water infiltration/permeability rates, amount of surface stability, protection for the plants/soil rootzone and resistance against compaction forces.
Too much thatch or organic matter anywhere within a green profile is invariably problematic. It will create many problems such as soft/un-resilient playability, greater disease incidences, excessive water retention, anaerobic soil conditions/poor gaseous exchange, increased dry patch, insulation of cold/hot soil temperatures, promotion of shallow-rooted grass species, whilst restricting root growth in desirable grasses through premature root ageing. Too little thatch and the greens may become too firm, eventually leading to thinning sward quality problems affecting ball-to-surface performance and management requirements.
Humus-like organic matter within the rootzone profile beneath the thatch is needed to help stabilise soil pH, retain moisture and nutrition for plant development as well as providing environmental stability for soil-based micro-organisms in which to function. This will hopefully help break down thatch and release nutrients. Too much or too little soil organic material and these highly beneficial aspects that we all rely upon will be negatively affected.
Organic matter builds as plants process tissues through growth/development such as roots, stolons, rhizomes, crowns, stems, leaves (short-term), and perhaps any off-green contamination that may enter the system.
Grass species and growth habit, rate of sward growth, rate of micro-organism function, drainage quality, type and the suitability of thatch management programme as well as local climatic conditions, will all collectively influence organic matter amounts and its quality. Different plant tissues also break down at different rates because they vary in complexity as well as the environments they are in. If there are significant differences in organic matter content between greens, one or more of the above influences may need to be managed to bring balance.
Benchmarking organic matter quantity and quality
STRI's ongoing research and practical experiences have concluded that the ideal range for organic matter quantities on a UK golf green lies between 6.0 and 7.0% (20 mm depth) by volume. The amount of organic matter falls as depth increases by approximately 1% for every 10 mm. We thus have a good idea of the target values we need to aim for, but how can you go about accurately measuring and recording on a site-by-site basis?
Four to six cores will be needed per green taken in a "clock" pattern (3, 6, 9 and 12) to ensure even sampling coverage. A width of about two-thirds of the distance from the centre of the green to the edge should be followed. The depth should be at least 100 mm to allow for any surplus needed when processing the samples. Our recommendation is to sample three to four greens per annum including known firm and dry greens, the worst offenders in terms of softness and any with agronomic problems. The time of year is not so important unless you are planning a season management programme, in which case the late summer is advised.
Once received, the sample is put through a process that accurately measures thatch and organic matter amounts at different depths in the profile. Qualitative assessment at the time of field sampling can be undertaken in addition to other data recording. It is the quantitative and qualitative assessments in combination that are of value to us. The important benefit of the testing is that by measuring organic matter at various depths within a green profile, we can assess specific areas where improvement is needed. We test at 20 mm depth increments, that is 0-20 mm, 20-40 mm, 40-60 mm, 60-80 mm and 80-100 mm horizons.
A process of burning the organic matter establishes organic matter content. This is very accurate unlike the digestion method sometimes employed. Testing at the measured depths is the only way to fully understand your profile and address organic matter problems. Ordinarily, in routine soil analysis only the average is taken over the total sample depth (normally 100 mm), invariably producing a misleading result in certain situations. Furthermore, often the key area of the sample, i.e. the thatch top, is disposed of and only the soil harvested. It may be that the lower depths are already at target levels but it is the surface accumulations which are the problem. We need to understand this.
It becomes much easier to plan, implement and justify de-thatching/organic matter control operations when target values are known about the green in question, together with a full understanding of what machines are best used to yield the best return. Once the targeted areas (particular greens and/or certain depths within the profile) and the nature of the problem are understood, specific treatments can be developed. In some cases we may be talking about micro, not macro, management. For example, green 6 may need an extra pass with the scarifier as opposed to the others.
This testing process should be viewed as another key information gathering tool that will provide an insight into necessary thatch/organic matter management programmes. It will also help you set an accurate benchmark with regard to progress, both initial and ongoing.
Thatch and organic matter affect so many key performance-related aspects of fine turf. We should treat thatch and organic matter management in a more controlled, measured way if we are to secure success and avoid any troublesome secondary problems.
The author and his clients have found this information tool very useful since it was provisionally released last year, and it has been used to answer many performance-related questions whilst influencing positive decision-making.
STRI Turfgrass Agronomist for the Central Southern Region