Photograph 4: Grass root zone inoculated with a granular mycorrhiza product
Photograph 5: Granular mycorrhiza amendment in the reconstruction of a sand-based golf green
Photograph 6: Non-treated sand-based golf green
Mycorrhiza spores and propagules can be strategically applied in various forms to aid the establishment and recovery of turf, especially in soils that are relatively sterile or depleted in nutrients
T
here are various types of mycorrhiza, which form different forms of association with different plant
groups. For example, a type of mycorrhiza that forms external attachment to the roots of predominantly woody species is ecto-mycorrhiza. Sometimes these ecto- mycorrhiza structures can be seen with the naked eye, especially on trees such as pine or silver birch, when a rooted plant is taken out of a pot (see photograph 1). However, grass plants form attachments with endo-mycorrhiza that result in the growth of the mycorrhiza structure inside the roots of the plants, therefore they are not visible to the naked eye, only under a microscope (see photograph 2).
Plant benefits of mycorrhiza
Mycorrhiza influences the growth habit of grass by stimulating the plant to root and, therefore, enhances the performance of the rooting structure in all its activities. This results in:
1. More efficient nutrient adsorption (especially N and P) from the soil
2. Improved water uptake and water use efficiency
3. Increased grass tolerance to saline and polluted soils
4. A more robust plant that is more able to withstand stress
When a good root system is established in the grass plant then, obviously, the general vigour and robustness of the plant is increased. However, there can be other secondary benefits such as improved drainage (due to increased root channels in the soil) and, probably most importantly, a greater efficiency in the use of soil nutrients and therefore a rationalisation of fertiliser applications, especially at plant establishment.
Applying mycorrhiza
Whilst mycorrhiza is naturally occurring, when turf is managed the mycorrhiza is generally lost and so, most often, levels of mycorrhiza in the rooting zone are either low or non existent. Therefore, at critical
periods in the establishment or renovation of the turf, it is strongly advantageous to assist the plant roots by applying a mycorrhiza inoculant into the root zone. Mycorrhiza spores and propagules can be strategically applied in various forms to aid the establishment and recovery of turf, especially in soils that are relatively sterile or depleted in nutrients.
On the other hand, in situations where turf is well established, with plenty of nutrients or water available and the plant is well rooted with no obvious rooting stress the application of a mycorrhiza product is likely to demonstrate little or no benefit. Where predominantly sand-based surfaces are constructed, or regularly topdressed, it is relatively easy to demonstrate the benefits of adding a mycorrhiza product in a trial situation. Photographs 3 and 4 illustrate this in a demonstration trial conducted by grounds staff at Birmingham University. The golden rule when applying any
mycorrhiza is to ensure that it reaches the roots of the grass plant, as it has to be in close proximity to the root so that it forms an association. This is easy when applied in a rooting zone for new seed or where fresh turf is being established. However, in established turf, the method used for application is to sweep the applied product into aeration holes. Therefore, application at the time of hollow coring or tining in spring or autumn is the best approach.
Best uses of mycorrhiza products
As already mentioned, it is not universally beneficial to apply a mycorrhiza inoculant to turf in all situations but, instead, to use it strategically where there are likely to be rooting issues or it is desirable to give the newly established plants a competitive advantage. Therefore the situations where the addition of mycorrhiza is likely to show most benefit are:
1. In the seed bed when sowing 2. Under newly laid turf
3. Worn and stressed areas 4. Included in divot mixes 5. Drought-prone turf 6. After de-compaction or turf aeration As photographs 5 and 6 show, at least
where sand-based greens are concerned, a mycorrhiza inoculate demonstrates itself as a cost effective investment. This is true for not only the establishment of the grass but also its ability to take up greater amounts of the fertiliser that is applied to the soil, before it is lost through the soil profile. Unlike bacteria, which are more sensitive to extremes of pH, the performance of mycorrhiza fungi is more closely related to the ability of the plant to grow. Therefore, if the conditions are right for grass growth then mycorrhiza will be able to form an association with the roots, provided it is placed in the rooting zone of the grass plant, either at establishment or at aeration.
Summary
Although mycorrhiza is not a 'silver bullet' for all problems it has its uses in a modern turf management strategy. The encouragement of soil microbial systems, that includes the application of mycorrhiza, is a useful biological tool in efficient turf management that allows a manager to use their turf inputs more efficiently, encourage a more robust and tolerant plant whilst also minimising their use of other synthetic products. Each turf manager needs to assess their situation and need, but good quality, appropriate advice is available if required.
Common questions answered
Q: Can mycorrhiza be used to overcome rooting problems in established turf?
A: Yes it can, but only once the original cause of the rooting problem has been addressed. It is not a miracle cure that overcomes all problems, but rather an aid to recovery and establishment, providing the original reason for decline has been alleviated.
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