Best Technical Merit Answers- May 2003
Following the success of the Technical Merit Award 2003, sponsored by Tillers Turf. Pitchcare have started to publish some of the best answers submitted to the monthly scenario questions. This month we have the best of Mays answers. Next week the best answers to the June scenario question will be shown.
May Scenario Question:
Explain why an active and diverse soil microbiological population is important in the management of healthy turf. Suggest possible effects on the functioning of the microbial community if the sports surface:
1. Was seriously compacted.
2. Was not fertilised.
3. Was regularly sprayed with fungicides.
1. Seriously compacted soils have higher bulk densities; therefore they contain less pore space, and less air, resulting in a reduction of aerobic microbial populations, and an increase of anaerobic microbial populations.
Soil air is contained within soil pores and provides aerobic microbial populations with a supply of oxygen, however even in well aerated soils there are still anaerobic microbials, because there will still be areas within the soil of no oxygen. In general the amount of aerobic and anaerobic microbials in any given soil are 'in balance' with each other, at all times dependant on the availability of oxygen.
Both types of microbials are vital for soil health, and subsequently turf health, so a healthy balance should always be maintained. We upset the balance by compacting our surfaces through use, so it is essential to aerate to readdress the balance. "If we never compacted the land, we would not need to aerate it!"
2. If the land was not fertilised the microbial population would be maintained within the soil at sustainable levels, dependant on the availability or minerals such as nitrogen from other sources, such as mineralisation and, atmospheric nitrogen fixers. Over time atmospheric N fixers (e.g. clover) will infiltrate the sward, because they have a competitive advantage - they have their own supply of N, and help sustain microbial populations.
Fertilisers in the past were never added to any crops before human activity managed the land; therefore plants, environmental factors and other organisms, such as microbial populations did the job for us, and are still doing so! However intensively managed sports turf has clippings removed (an organic supply of N), require further applications of N to cope with increased stress, and N losses due to irrigation (leaching).
Applications of N to a sward help to maintain the Carbon: Nitrogen ratio in the soil for microbial populations. Adding N to the soil increases populations, but also increases thatch accumulation, and encourages 'lush' growth, possibly at undesirable times of year. Correct N management of soils is essential to maintain healthy swards, healthy soils and their population of microbials.
3. Adding regular amounts of fungicide to a soil will kill any fungi in the soil, beneficial or not, resulting in an increase in thatch. Fungi are also an important ingredient for a healthy soil, with only a few undesirable types, which attack turf. Some beneficial fungi control the undesirable fungi, so if fungicides are used there is no 'natural' resistance in the soil.
The other problem with this situation is that the fungi will eventually become immune to the fungicide used, particularly if it is the same product used each time. If there is no natural resistance and chemicals have a limited effect, what is left to use?
Maintaining active and diverse microbiological populations is important for the management of fine turf. Finding and maintaining the correct balance of oxygen, nitrogen, and other important factors is essential for soil health and subsequently turfgrass health. Fungicides are sometimes necessary, but should not be overused or relied upon for turfgrass health. The cultural control of turfgrass pests, and correct management of turf and soils is the key to future success.
Massive diversity exists among turfgrass-soil micro organisms. It is said that more biological diversity exists among the micro organisms in an ounce of soil than in the entire Amazon rain forest. This diversity is important in the maintenance of optimum soil and turfgrass health.
Micro organisms perform a variety of functions, many of which are extremely important to the health of a turf. Chemical, physical and biological factors strongly affect their level of activity as well as the kinds of micro organisms present. Factors such as soil pH, fertility, organic matter, moisture, temperature, soil porosity, and turfgrass species and cultivar all are important. As a result, anything that alters these factors also affects microbial activities. When management practices affect microbial processes in a negative way, we generally see the indirect effects as reduced plant health and vigour. When practices have a positive effect on microbial populations, we often see improved turf vigour, stress tolerance and pest tolerance.
A bacterium plays an important role in maintaining the balance between thatch accumulation and reduction, and, to some degree can be managed by enzymes, which can be applied to the surface. Some bacteria impact turfgrass health by controlling turfgrass pathogens. These bacteria inhibit pathogens by competing for resources, producing antibiotic compounds or acting as fungal parasites.
1. Adequate soil-oxygen levels are extremely important for soil micro organisms. If the soil is seriously compacted there is the potential for anaerobic conditions to develop. Aeration of compacted soils will enhance microbial activity in the Rhizosphere.
2. Consistent fertility is the key to a healthy microbial community in soils - "feast or famine" cycles of nutrient availability will have a negative impact.
3. Regular spraying with fungicides need not necessarily lead to problems on turf. However, in agricultural crops, fungicide resistance has been seen to develop when the same fungicide was applied repeatedly over a number of years. In order to avoid this potential to occur in turf, it may be preferable to rotate the fungicides used.
Some fungicides do have an anti-microbial impact and their use should therefore be limited - if routine fungicide application appears necessary, it may well be worthwhile considering whether an adjustment to the cultural techniques employed may enable the green-keeper to tackle the cause of the problem (i.e. insufficient scarification or incorrect application of fertiliser), rather than treating the symptom as it occurs.
1, A dynamic, fully functioning micro-biological (MB) population is important in the management of healthy turf because:
a) Antagonistic micro organisms (MO's) (the goodies) strongly assist in staving off the onset of disease pathogens thus helping to keep serious disease outbreaks at manageable levels.
b) They assist in the breakdown of applied nutrients into simpler forms, which are then readily assumable by the plant. I.e.: ammonium compounds > nitrites > nitrates
c) A healthy soil environment brings about mycorrhizal associations whereby MO's attach themselves to plant roots and function to each other's mutual advantageous co-existence. - (Symbiosis)
d) Healthy MB numbers help in the decomposition of thatch feeding on dead and senescent organic matter thus reducing rapid thatch formation.
2. a) Seriously compacted soil inhibits the healthy existence of aerobic MO's because of the severe reduction of available soil oxygen. Compacted soil has few or no air passages in its structure.
In compacted soil the reverse occurs. Instead of an atmosphere, which encourages a flourishing 'good' MO proliferation, conditions become anaerobic (lacking in free oxygen), in turn giving rise to MO's, which ultimately create a foul, putrid soil atmosphere.
b) If a turf surface did not receive fertilizer the already unnatural environment i.e. closely mown or severely worn sward would lose vigour and gradually produce less foliage.
This would eventually lead to a depleted sward, bare earth and a reduction in fresh supplies of organic matter; (nutrient base for MO's).
c) Sports surfaces that receive regular applications of fungicide face the risk of ending up without, or at least a greatly depleted micro-biological population.
Fungicides are not generally selective and therefore wipe out pathogens both useful and undesirable, creating greater vulnerability of the sward to disease attack and other physical malfunctions.
Part 1. We must keep an active and diverse selection of microbes in the soil in order to keep the whole area balanced. This will keep the plant healthy and encourage the nitrogen cycle naturally. If you have too many good or bad bacteria, it will upset this balance. These good bacteria or microbes will help in the breakdown of thatch and encourage good cationic exchange rates. Unfortunately the bad has to live with the good, but it is our job to keep the good guys on top. We all have, say Fusarium spores (the bad guys) in our turf, but if the good guys are on top they will stop them causing too many problems and would also aid recovery from any attack.
Part 2. Obviously the sports turf we manage is a very fragile climate and again it is all about balance, using the tools we have to maintain that balance. These tools could be mechanical or chemical but we must judge, as turf professionals, their timing and usage.
Compaction causes all sorts of problems to all turf managers, be it football, golf, tennis, bowls etc, but the main effect is lack of oxygen getting through the soil profile. These anaerobic conditions cause the microbes in the soil to die, as even these need air and space to survive.
If you do not fertilise your turf with a balanced programme, it will not survive all the stresses we put on it for one, but more specifically we need to encourage the healthy microbes and give them food to thrive. If we feed the turf properly, we will be producing the right amount of thatch for them to digest and live in, but not too many for them to cope with.
The use of fungicides has to be strictly regulated, as the use too often of them will, in effect, sterilise the soil. Then we would have to start the whole business again of building up the balance between good and bad and at the times of the year when we use the bulk of our fungicides, the good microbes are at their least active, meaning the ones we don't want are likely to get a good head start on those that we do.