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ground food chain and 50% goes back into the soil via the roots and thatch to feed the underground mostly invisible food chain. It is the underground invisible food web that must be cultivated to manage disease and grow the fine grasses needed for a good playing surface.


Out of Sight


Out of sight used to be out of mind but, using molecular analysis and electron microscopes that allow identification of individual bacteria, fungi and other organisms, we can now start to understand how natural processes work in sports turf rootzones and how to use them to our advantage. Food underground comes from


exudates from plant roots, in the form of protein (like in eggs,) sugars and carbohydrates (as in flour), the ingredients to make pancakes or biscuits,


Fig 1: The


underground Soil Food Web, picture courtesy SoilFoodWeb Inc


nitrate, trace elements and water and feed them to the plant, giving the plant a vastly extended root system. Mycorrhizal grass can grow many times faster than grass in sterile soils. (see Fig 2) It must be said that there is much to discover about how all these bacteria and fungi interact but we do know how they fit into the food chain.


In a gramme of healthy soil you may find about a billion bacteria weighing about 100µg and a similar weight of fungal biomass, only half may be active but for rye, fescue or agrostis grass growth it is important to have approximately equal bacterial and fungal biomass, whereas poa annua grows in poor bacterial dominant soil.


How nitrogen gets into the grass


Some bacteria fix nitrogen from the atmosphere, others take it from root exudates in the soil. Locked up in a bacterial cell or fungal hyphae nitrogen is not available to the plant. The microbes have to be eaten by the next stage of the food chain comprising protozoa and nematodes. There may be 10,000 protozoa in a gramme of soil but only a few hundred nematodes. Some nematodes can be seen with a magnifying glass. Protozoa and nematodes eat the bacteria and fungi, they use the carbon to grow and excrete excess nitrogen as


this is the main food for bacteria. When grass dies it becomes thatch full of cellulose and lignin, this is the favourite food of fungi which converts dead grass, leaves and twigs to humus - the nutrient store and foundation for future plant growth. Bacteria and fungi form the foundation of the whole food chain. The good (saprophytic) microbes only live on dead matter. There are about 20,000 enumerated soil bacteria and 15,000 fungi Ingham et al, of these most turf managers know the few disease causing (pathogenic) fungi which live on live plants by name.


Mycorrhizae


There are also fungi which live on carbon and sugars inside the grass root. To stop the plant from dying through lack of carbon these fungi called mycorrhizal fungi use their hyphae to suck up phosphate,


ammonium, which feeds the grass when converted to nitrate by nitrifying bacteria in the presence of oxygen There are four types of nematode, bacterial, fungal and root eating, and predators which eat other nematodes. Fungal hyphae and nematodes naturally aerate the soil, they create small spaces in the soil leaving little tunnels full of excrement (ammonium) for roots to grow into and feed on and so the chain expands up to moles and other burrowing animals. Working together all these microbes and organisms ensure a constant supply of nutrient for the plant, avoiding the boom and bust of the fertiliser cycle, they protect the grass from disease,


because if the grass dies the


whole food chain dies, and recycle dead grass back into usable


nutrient For sports turf purposes we try to stop the food chain at non-casting worms but, up to that point, all aspects of the chain are necessary for natural healthy grass growth.


Why are sports turf rootzones sterile?


Plants have evolved growth mechanisms in association with soil bacteria and fungi over millions of years. Ammonium sulphate has a salt index of 0.7. Dumping a tonne or more of ammonium sulphate (salts) per hectare per year means that the plant is swimming in a sea of food and mineral salts. The plant takes up nutrient by osmosis and does not need its associations with microbes to live, which coupled with the fact that bacteria like sugar, not salt, excess water and compaction which deprives the microbes of oxygen, the removal of animals which replenish the microbes via excrement and near daily cutting mean that the food chain cannot possibly survive. We often find that sports turf root zones have less that 1% of the microbial biomass, and that the total fungal biomass is much less than total bacterial biomass though, as we shall see, fungi are extremely important to your greens management programme. You can now see the reason for adding bacteria and fungi and special food sources is to re-establish the bottom rungs of the soil food chain.


How does this help the turf manager? Disease management


If the grass dies we all starve, so nature has worked out some clever tricks to keep the plant and food chain alive. Figure 3 is a root covered in mycorrhizal and other fungi which shows blue in the picture, you can hardly see the root for fungi. It effectively forms a barrier against any disease-causing organism that wants to penetrate the root.


Fig 3


The good fungi and bacteria also get to any freely available nutrient first and out compete the pathogens, this is called competitive exclusion. A third way that beneficial microbes keep their host plant alive is to produce antibiotics against disease-causing organisms. Finally, in times of stress and food shortage some microbes eat other microbes, the bad guys are usually the first to go in this


Fig 2: The roots on the left inoculated with mycorrhizae and soil fungi


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