Technical


Healthy, humus rich golf green rootzone


Soil


Organic Matter is Good


Soil organic matter has come in for some bad press recently, much of it unjustified, says Symbio’s Martin Ward


O


rganisations providing “organic matter” tests often give the impression that there should be a


maximum level of organic matter in a rootzone to give good playing characteristics. This is often interpreted as all organic matter is bad, which is not correct. In the following article, we look at all the benefits soil organic matter brings to your sward and playing surface. The first point to make is that thatch should not be confused with all the good organic matter in the soil. Unfortunately, the loss on ignition test that is used to measure organic matter is a simple measure of carbon, and it not only measures thatch, but also roots, organic fertilisers, partially degraded humus and humic compounds, humus, the microbial biomass, which can be up to 3 tonnes per hectare. I suspect very few turf managers would worry about an organic matter reading of 5% if it was all roots and humus.


Strictly speaking, thatch should not be called soil organic matter, but organic material. In managed sports turf systems, thatch is almost the only source of the beneficial soil organic matter which is the nutrient store and engine room of the


rootzone. If the soil is the stomach of the plant, then soil organic matter is the stomach lining without which there would be no natural plant growth. In a healthy rootzone, there


are four types of organic matter - living, dead, very dead and extremely dead. The living comprises roots and soil organisms, but it is the dead organics we will concentrate on here. The dead component comprises thatch, which should only comprise about 10-20% of the total organic matter. Thatch takes a few weeks to two years to break down into what is known as the very dead or active fraction, which is organic matter still decomposing, and makes up 35-50% of the total. This fraction supports much of the biological activity in the rootzone. The extremely dead portion is humus which contains very little organic content but is essential for healthy plant growth and makes up a further 35-50%, and can take up to thirty years to become completely mineralised. There are a lot of


misconceptions about the role of soil organic matter, but it actually drives the physics, chemistry and biology of a healthy rootzone. Put in perspective, 1% soil organic matter in the form of humic


“In a healthy rootzone, there are four types of organic matter - living, dead, very dead and extremely dead”


132 PC DECEMBER/JANUARY 2014


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