Technical
increasing amount of information being processed, we are finding that greens moisture content can be brought under better levels of control, despite weather experienced. The answer, for many greens, lies in its organic matter levels.
Default moisture setting
Determining the moisture content contained within the upper profile (0- 6.5cm) during periods of perceived soil saturation can tell you a lot about the nature of your greens and, indeed, organic matter contained within them. For many, it is often perceived that saturated greens during wet periods are largely a result of weather and, therefore, outside of our control or, similarly, put down to an underlying drainage problem. Perhaps, in some unique cases, this may be correct but, with ever increasing amounts of organic matter and moisture content results, we are finding moisture contents, although not completely controllable, can be managed better through creation of healthier soil profiles and lower organic matter content, giving lower year round average ‘default’ moisture contents. This has several agronomic advantages to course managers and their clubs.
The impact of organic matter on moisture content throughout the year
Depending on various organic matter levels, we are finding moisture contents to behave in various ways through the year. Using a typical UK climate - noting variability from north to south - the model (right) provides general classification of moisture behaviour in relationship with organic matter (LOI %) contained within the upper 0-40mm. In contrast, where moisture contents
are suitably low, the retentive nature of the upper profile is notably reduced and target moisture contents can be achieved for larger portions of the year. Again, where organic matter is well above desirable ranges, moisture contents will spend large portions of the year outside of desirable moisture ranges and, indeed, out of our manageable control, leading to several negative agronomic characteristics.
Achieving low moisture contents with high organic matter
This model isn’t to say we can’t achieve low moisture contents with high organic matter. At points in the year, regardless of organic matter levels, sustaining low moisture contents can be achieved. Managing moisture content at low levels (15-25%) with high organic matter (12%>) content is more than possible, but does come with very high risks and’'knife-edge’ management. Dry patch almost becomes a certainty when trying to drive moisture contents low with high organic matter, and intensive preventative management is required.
The depth of moisture retention
It is easy to generalise and the term soil moisture content in itself could be considered just that. Looking further into
118 PC FEBRUARY/MARCH 2013 A combination of high levels of organic matter, a dry summer and a week of neglect 17-23% <17%
Volumetric Moisture Content Target species 35%> 27% > 23-27%
Playing quality
Encourage poa annua Very soft Encourage poa annua
Stress poa annua and
encourage bentgrass and fescues
Drought poa annua and Promote very firm greens encourage fescues
Summary impact of average soil moisture content on species composition and playing quality
soil moisture, it can be further divided into soil moisture at bespoke depths, for example 0-30mm, 30-60mm, 60-100mm and so on.
On average, moisture content in the upper 0-30mm of the soil profile has been 20-40 times higher than that of moisture content at 40-60mm deep in the profile. Further decreases in moisture content at depth are commonly experienced until heavier silt/clay soils occur or, in USGA greens, no increase is experienced. It is not surprising to state this trend replicates itself in the presence of organic matter content, which generally decreases at 20mm depths in the soil profile.
15%> 10-15% 6-10% 4-6% 2-4%
Summary of organic matter and moisture content relationships within a UK climate with cool season grasses
Average moisture content present 40%> 30-40% 25-30% 20-25% 15-20%
NB: The model is provided to show general moisture trends in relationship to LOI organic matter levels found in greens.
Exceptions to these trends can be achieved and will be subject to climatic conditions present at those times. Results do, however, provide an accurate summary of trends.
This information alone, when applied to a course manager’s own greens, can assist greatly in deciding the requirements of sand dressing material or products on greens, and at which depth in the soil profile they are required.
The impact of higher moisture content on organic matter accumulation
Throughout this article moisture contents have been referred to as a percentage figures. If we estimate 40-50% of the soil profile is solid mass (silt, sand, clay and organic matter), the rest is made up of water (moisture) or air to varying extents. For decades we have been taught about
OM/Month J F M A M J J A S O N D Promote soft greens
Encourage bentgrass in Promote moderate firmness poa annua mixture
Promote firm greens
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