Technical - Soil Biology
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Golf Club Spillern in Austria has had success using the methods described.
Inset: roots with mycorrhizae (left) - roots without mycorrhizae (right)
The importance of Cation Exchange Capacity
CEC measures the ability of the soil to hold on to the positive ions of key nutrients. Alkaline nutrients with positive ions include calcium, potassium and magnesium, whilst acidic nutrients with positive ions include hydrogen (which determines pH), ammonium and iron. Many sands used in construction have a CEC of less than 2 meq+/100g, whereas the ideal for a turf rootzone is above 10. This means that a lot of the fertiliser applied just leaches away and is wasted.
CEC is raised by increasing the negative ions in the soil. In natural soils, this is achieved by increasing humus or clay. Clay is not wanted and humus is in short supply in turf rootzones, unless you incorporate a lot of organic matter. To maintain the drainage properties, the most common way is to add zeolite mixed into the rootzone. Zeolites, like humus, have a CEC of between 150-250 meq+/100g, so mixing zeolites at 5-10% into the rootzone is a quick and relatively inexpensive way of creating beneficial CEC before sowing. If budgets do not stretch to adding 5%, any addition will be beneficial in the short and medium term.
Base Saturation
On almost every chemical soil analysis, you see the base saturation calculations. This measures the proportions of the alkaline nutrients calcium, potassium, magnesium and sodium. Most agronomists agree that a Ca:K:Mg ratio of about 7-10:2:1, with exchangeable calcium at a minimum of about 700ppm, is favourable for good grass growth. The rootzone can be analysed before construction and these essential elements, together with phosphate
The rootzones used for most new sport turf construction are almost completely devoid of the biology that supports grass growth in the natural environment
and trace elements, may be mixed into the rootzone before building to ensure the correct balance is present from the start and prevent excessive applications of fertiliser to the newly growing grass.
Preseeding Nutrition
Young plants need proteins and carbohydrates to grow, in addition to NPK and trace elements. They grow best when low salt, slow release organic fertilisers are used. Some elements, like calcium, potassium and magnesium and the trace elements iron, manganese etc. have to be applied in mineral form; however, nitrogen and phosphate can be applied mostly in slow release organic form as a preseeder fertiliser.
Organic fertilisers can be mixed so that a mixture of organic sources are used combining the proteins and carbohydrates from vegetable sources, e.g. molasses, with the slow release organic substrates from composted animal manure. Both sources of organic nutrient act as an excellent substrate for the soil microbiology that must also be added.
Traditionally, high levels of phosphate are applied but, for the last twenty years, it has been shown that grass grows best when inoculated with mycorrhizal fungi at relatively low levels of available phosphate between 7.5 and 15ppm.
If mineral fertilisers are used, it is best to use those with a low salt index.
Post seeding nutrition
The amount and type of nutrient required depends very much on grass species, climate and the time allowed for the grow in. In the next section, we will be looking at ways to create the correct biology for perennial grass growth and the best fertilisers to promote healthy biology are primarily organic fertilisers rich in humic and fulvic acids, or low salt index mineral fertilisers plus biostimulants.
It is, of course, possible to force grass with high levels of nitrogen and phosphate, but this creates rapid thatch production and also the conditions for subsequent poa annua invasion, giving long term pain for a short term gain. When appointing contractors to grow in a pitch or golf course, care should be taken to ensure the correct nutrition is specified for the long term benefit of the sward and rootzone. This will save thousands of pounds in the long term maintenance of the sward.
When the physics and chemistry are in good order, we can introduce the beneficial soil biology.
Roots without mycorrhizae (top) in contrast to roots with mycorrhizae (bottom) as seen at Golf Club Spillern
PC JUNE/JULY 2016 I 123
Creating the correct soil biology
The rootzones used for most new sport turf construction are almost completely devoid of the biology that supports grass growth in the natural environment. In a previous article, we looked at the correct biology needed in the rootzone for continued perennial grass growth,
https://www.pitchcare.com/magazine/effect-a- stress-free-change-to-fine-grasses.html.
The main microbial components of a healthy rootzone and sward are:-
Bacteria - which live mostly on root exudates and provide a barrier to disease, recycle nutrient and create friable soil whilst converting ammonium to nitrate
Fungi - which degrade cellulose and lignin, convert thatch to humus and produce toxins against plant diseases. For rapid grass growth, the most important form mycorrhizal associations with the plant.
Protozoa - which eat bacteria and produce ammonium
Nematodes - which eat fungi and bacteria and create space for root hairs while producing ammonium
Mycorrhizal Fungi
Some fungi form mycorrhizal associations with the plant and are the most important for rapid grass growth. Myco=fungi and rhizae=root, i.e
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