vigorous growth habit. At the other end of the scale there are less aggressive growing species, such as the fine fescues, which can produce significant thatch due to their leaves, nodes and crowns being extremely resistant to decomposition due to their high lignin content. Although, with fine fescues, thatch levels take longer to accumulate than do other more vigorous growing grass species, their recovery rate is slower and therefore, any mechanical dethatching operation should be carried out in a less severe manner than with other grass species. The soil pH can have an adverse effect on thatch development and, as the pH decreases, thatch is likely to increase - this is predominantly due to acid soils having a negative effect on microbial populations, reducing the potential for decomposition.
High applications of nitrogenous fertilisers will promote excessive thatch through the production of lush, succulent shoot growth. The applications of fertilisers containing the ammonium form of nitrogen, for example, sulphate of ammonia, are likely to increase acidity, while nitrate-containing fertilisers such as potassium nitrate may cause the soil to become more alkaline. Excessive irrigation practices can cause soils to become waterlogged, resulting in reduced oxygen levels and inhibit microbial populations. There is also the potential of plant nutrients being lost through leaching.
What effects will thatch have on turf quality?
Excessive thatch will decrease the vigour of turf grasses by restricting the movement of water, gas exchange, nutrient availability, cold tolerance and drought stress tolerance, pesticide movement and degradation, and likely to increase pest and disease incidence. Soft, spongy greens can quickly become saturated, while the soil immediately below can, in some cases, remain dry. An increase in thatch levels will reduce root depth and, as a result, grasses become more susceptible to changes in temperature. This can contribute to causing a hydrophobic condition (dry-patch) whereby soils may not necessarily be compacted but are hard to re-wet. This is thought to be associated with certain disease pathogens producing a waxy coating or secretion
be resolved simply by aeration
surrounding soil particles or thatch, thus preventing water penetration. Thatch will have a negative effect on diffusion, the exchange of gases, oxygen (O2
) and carbon dioxide (CO2 ) between
the soil air spaces and the atmosphere, which will ultimately effect root development - with a reduction in oxygen and possibly an increase in carbon dioxide (CO2
and vigour and therefore, must surely increase disease incidence.
Options to control thatch toxicity) young root
tips will die and older roots can become non-functional.
Thatch can effect the movement of nutrients by preventing penetration through the soil surface. Water soluble nitrogen sources are more likely to be lost to volatilisation, while non-mobile fertilisers, such as phosphorous, may not penetrate the thatch layer. Excessive nitrogen levels will induce rapid, succulent shoot growth, which is prone to scalping by mowing equipment and is frequently more of a problem on heavily thatched greens. Root growth, disease resistance, temperature, drought and wear tolerance is reduced as nitrogen levels are increased.
The rate and efficiency of pesticides can be affected by excessive thatch which can act as a second canopy layer through which pesticides must pass and which can physically bind the pesticide, reducing its ability to reach the target area. This could possibly reduce leach loss but may also reduce pesticide efficiency. Once a thatch becomes hydrophobic it can reduce pesticide efficiency by inhibiting penetration or causing runoff. Thatch will harbour many types of disease pathogens waiting for environmental conditions to favour their activity. They survive as resting structures or saprophytes (organisms which live on dead organic matter) in thatch. For many turf grass pathogens thatch provides the perfect moist environment, but some say that most turf grass pathogens are airborne and, therefore, thatch cannot necessarily increase disease incidence. However, evidence suggests that excessive thatch reduces turf grass health
The prevention of excessive thatch is managed by cultural practices through either mechanical or biological means. Biological control is linked to maintaining a healthy environment in order for micro-organisms to decompose thatch. It is important to remember that thatch accumulates over a period of time and the more vigorous species, such as bent grass, may produce excessive thatch, and, in a new green construction, in just two or three growing seasons. So, from the early days of establishment, it is important to understand the growth habit of the grasses you are managing as this will dictate the kind of management regime you implement. If you inherit a thatch related problem then it is advisable not to attempt eradicating the problem in one season, but programme a series of operations over a period of one or two years, ensuring that any operation is carried out when environmental conditions favour thatch removal i.e. grasses are actively growing, thatch is moist and temperatures are adequate to support active growth and a rapid recovery. As previously mentioned, thatch can be
produced through various physical or environmental conditions, and the resulting characteristics of the thatch can alter from soft and holding water like a sponge, to dense and tightly bound, preventing moisture penetration. So, totally different management programmes may be required. However, increasing oxygen to the soil environment will go a long way towards solving the problem. Fifty percent of thatch related problems could be resolved simply by aeration. Unfortunately, however, the more disruptive form of aeration the better the results. Hollow coring is undoubtedly the quickest and most effective way in which
39
Fifty percent of thatch related problems could
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