There has been a lot of discussion on the use of compost teas in turf management since the RAC Country Club started using it in 2003.
The philosophy is simple, you either get the soil to work for you and reap the benefits of plant and soil evolution, or use soil as a receptacle for chemicals. The use of compost and compost teas is the simplest way to develop healthy soil, maximise yields and minimise chemical inputs.
Unfortunately, compost is almost impossible to apply to golf and bowling greens, cricket squares and other areas of fine turf. But, compost teas give you most of the benefits of adding compost without the increase in organic matter and the problems that causes. It is also an easy way to reintroduce soil life to compacted waterlogged football and rugby pitches.
What is Compost Tea?
Compost tea is an extract of a given compost of a given constitution. It can be either bacterial or fungal dominated but, in all cases, a good compost tea will contain:
• Enzymes and amino-acids
• Bacteria, fungi, protozoa and beneficial nematodes
• Water soluble nutrients and organically bound nutrients
The quantity, diversity and quality of these micro-organisms depend on the quality of the compost used for the extraction, the brewer used and micronutrients and starters added for optimum organism growth.
Compost Tea is not a product, but a solution to transport micro-organisms. It is a temporary survival unit that allows living micro-organisms to be taken from the compost, multiplied rapidly and introduced to the soil and leaf.
Why do we need living soil?
Typical sportsturf rootzones, that have been used as a receptacle for chemicals over the years, are effectively dead. These rootzones contain the limited biology suitable for poa annua, a grass that survives because of constant seeding and high nutrient water and pesticide inputs.
All plants rely on relationships with soil microbes that promote healthy growth. These symbiotic plant microbe systems, in which grasses, except poa annua, apply about 20% of their energy to root formation and leak about 30% of the energy they produce through their roots to feed the microbes forming the soil food web, have evolved over millions of years. In return, the microbes convert the proteins and carbohydrates that leak out of the root back into plant food available at the right time for optimum plant growth.
Soil microbes have a range of mechanisms to protect the grass against pathogen attack, aid in the decomposition of toxins and produce plant growth hormones. The net result of this is that grass grown in a healthy food web is stronger, needs less inorganic fertiliser and water, suffers less from disease, fairy rings and dry patch and tends towards perennial grasses not poa annua.
Compost teas allow you to match the correct biology to your grass from the day the seed germinates, so exceptional growth can occur.
How to make compost tea
There are three essential ingredients
A compost tea brewer - you can make your own. You need a container and an air supply, but you must have a container that is rounded so no anaerobic spots form, and an air supply that keeps the oxygen level at at least 6ppm all the time. As brewers start at about £160 it is better to get one that has been tried and tested to produce good compost tea.
Good compost - For fine turf you must apply fungal dominant tea, which means your compost must be rich in a variety of fungi (100% poa annua turf can have a bacterial dominant tea).
To make fungal dominant compost you need about 40% woody material, 30% high nitrogen e.g. fresh spring grass cuttings, alfalfa or legumes, 30% green waste and about 50-60% humidity.
You can start it with a compost starter but, within a few days, it should reach at least 65oC, when it is turned. It should be turned three times and be fully composted in about six weeks. It is essential that it gets hot to kill seeds and pathogens, otherwise you can brew all sorts of problems.
Again, it is better to buy compost that has been tested for fungal activity and proven to be free of pathogens. For sportsturf, NEVER use animal or human waste or discarded food in your compost, as this can transmit E. coli, Salmonella and other harmful pathogens to the leaf and soil.
The correct nutrients - You need to add foods to feed the bacteria and fungi so that they can grow when they have been extracted from the compost. Different foods feed bacteria and fungi, so be sure to use the correct nutrients for your brew.
If you develop your own brewer and compost you should have the compost and resulting tea analysed to make sure it has the correct ratios of bacteria, fungi, protozoa and nematodes. It is also a good idea to have your soil analysed for its biology so that you can make a compost tea that solves your problems. All reputable suppliers will have test results for their compost and equipment to confirm that you can grow active microbes
Benefits of compost tea
In previous articles in Pitchcare it has been explained how perennial grasses grow in a fungal dominant rootzone, while poa annua prefers a bacterial dominant food web. By applying fungal dominant teas you create the conditions for fine grasses without stressing the poa annua.
Thatch is also food for fungi which live on lignin and cellulose, so you will start to see thatch degradation and humus creation which, in turn, will allow better percolation and more air, so you get less black layer.
As the soil food web starts to develop, fungal hyphae and beneficial nematodes will move through the soil. These will push fine soil particles apart, increasing friability and assimilating the locked up nutrient. In time, the excess iron which causes iron bands and root breaks will be taken up by the plant, and the rootzone will become a rich brown colour as chemicals are replaced by humus.
Nutrient inputs are also reduced as the food leaked from the plant is converted back into ammonia by the protozoa and nematodes feeding on bacteria and fungi - it is quite common for high input users to see fertiliser requirements halve in the first year.
When you get fungal dominance in the thatch layer you start to outcompete the basidiomycetes that cause fairy rings, which cannot access the organic matter to release nitrogen to form the green rings, or release hydrophobic substances over the soil particles, creating fungal smelling dry patch.
Disease resistance is also improved because you have stronger plants, with a beneficial microbial barrier around the root system, helping to keep fungal pathogens at bay.
Sadly, most sportsturf rootzones are relatively low in the organic matter needed to support microbial life, even though a lot of microbial food leaks from the roots during photosynthesis, so fairly regular applications are needed. In an 80/20 rootzone you will need about 100 litres of compost tea per application.
Frequency of application depends upon what you want to achieve. To clean a chemically compromised rootzone, with iron bands, black layer, barriers of fines and root breaks, will need up to ten applications per year, starting in spring. If you have a relatively healthy rootzone and want to get good early growth, help manage dry patch and strengthen the grass in autumn, five or six applications appropriately timed may suffice.
In summary, compost teas are a simple, inexpensive way (less than £100 per hectare) of getting soil biology, chemistry and physics to work in harmony for healthy, sustainable fine grass growth.
Martin Ward, Symbio