Organic Matter I. What is it and how is it measured?

The organic matter present in the profiles of our sports surfaces in minimal percentages, they help the retention of water and nutrients and provide resilience to the putting greens. On the other hand, an excess causes clogging of the pore space and prevents free movement through the soil, resulting in "shaving", "cushioning" and soft surfaces, inconsistency in the rolling balling, moss growth and high damage due to ball impacts or "piques".

The best way to monitor the organic matter content of the soil profileThe analysis of different samples at different depths. Analysis of a single sample will not reveal good information about its content and physical properties.

The determination process involves drying the sample at 105 degrees Celsius to eliminate all the moisture. Subsequently, this dry sample, which has mineral and organic content, is weighed and placed in an oven for (at least) two hours at 360-440 ºC, thus eliminating the organic matter by calcination. When the sample cools down (up to 150ºC) it is weighed again, before it starts to absorb moisture from the environment.

The difference between the weights before and after the oven gives the weight of organic matter, which can be expressed as a percentage of the weight of the sample. It is important to always carry out the analyses with the same laboratory to avoid inconsistencies in the results.

Another method of determination is the method of Walkley-Blackin which a chemical reaction of soil carbon with an oxidising agent, potassium dichromate, is carried out.

One way of diluting the organic matter content is to carry out light and frequent topdressing, although it makes even more sense to use tools for calculating nitrogen doses based on growth needs, such as the tool I-Greenkeeping.

Other aspects to be taken into account are the influence on the saturated hydraulic conductivityThe number of new cases is usually reduced by up to 10% after 6 months after the creation of a green (Murphy. J.W (TGIF Record 28098) and Nelson, S.H (TIFG Record 1305)) and up to more than a 30-40 % decrease from the original conditions due to the accumulation of organic matter after two years (Neylan, J. 1994 "Sand profiles and their long term performance" Golf and Sport Turf Australia). McCoy recommends a maximum of 3.5% organic matter and warns that macroporosity declines from these values.

Factors that increase the organic content of our sports surfaces are as follows:

1. Cold temperatures in cold climate turfgrasses, as microbial activity declines and so does mineralisation.
2. Latest generation varieties with high growth densities.
3. Low level of aeration in the soil profiles, which leads to anaerobic conditions and stimulates superficial adventitious roots.
4. Inadequate or very light sanding.
5. Addition of organic amendments.
6. pH acids, below 5.5, which limit bacterial activity and actinomycete populations.
7. Maintenance with high nitrogen inputs.
8. Low earthworm activity.

Robert N. Carrow "Surface Organic Matter in Bentgrass Greens" USGA. Turfgrass and Environmental Research Online.