Best Technical Merit Answers- August 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 August's answers.
August Scenario Question:
August- Examine the importance of soil (root zone) compatibility when top dressing and explain in detail the methods of determining the correct type for your particular sport.
1) Soil compatibility is extremely important when dressing cricket pitches. If you don't integrate the dressing properly, or change the type of loam used, or a thatch layer builds up and gets incorporated, the result can be a soil profile with different compositions at different depths. This can create thin relatively compacted layers, with anaerobic water logging just above them creating ferromanganese nodules and black layer, may limit root depth, and can result in tops with poor cohesion or pudding pitches however much rolling you give.
To avoid this problem it is important when dressing to first remove as much thatch as possible, to deeply aerate or verti-drain with solid or hollow tines up to 10" deep, and to dress the pitch as evenly as possible. We have learned how important it is to always use the same dressing, e.g. Surrey Loam, from a reliable consistent source. Failing to do so can mean the pitch needs to be completely dug out and started again.
2) To select the correct top-dressing for your particular sport you would first have to have your soil analysed and tested by an agronomist to see particle size, top soil, what type and size top-dressing has been used before.
Once this has been done you need to decide what you want the top dressing to do if is used to level the surface or fill hollow tine holes etc. When we use top dressings to fill hollow tine holes we have 10% grit added, this is done to increase particle size therefore allowing the hole to remain more open. By doing this you get greater benefits from the operations water penetrates easier and it allows air to circulate.
When you know what type has been used before and the root zone that is already present you can decide on the type of top-dressing you require. It is best to continue with the root-zone that is already present because if you change the type of top-dressing it will start to form a layer on top of the root zone already there. If this happens roots may struggle to break through the layers and also if they do manage it will be a weak point in the roots and may break or snap.
On our golf course we use a top dressing of 45% loam 45% sand and 10% grit this is special mixed for us, as it is an individual need.
3) Top dressing is an important part of a turfgrass maintenance program, but care must be taken when topdressing to ensure that the desired result is achieved. Topdressing is used as a means of controlling or improving the surface and rootzone characteristics of all sports turf.
Topdressing on fine turf is used to restore the surface levels, making greens smoother and wickets truer, whilst on winter games pitches its use is directed at maintaining infiltration rates; removing excess surface water. Achieving a successful topdressing regime can depend on several factors, such as: whether the circumstances and weather for application are suitable, but primarily if the topdressing material used is compatible with the existing rootzone. Ensuring that any topdressing material is compatible with the existing rootzone is essential in maintaining consistent rootzones.
Inconsistencies in rootzones can cause root breaks, and texture breaks.
- Root break: An area within a soil profile that restricts the downward penetration of roots, either by Shear forces or compacted/ anaerobic conditions.
- Texture break: A condition when two or more layers of incompatible soil are present within a rootzone. The soils, being different will behave differently, one soil may dry quicker than the other forming a horizontal crack, which will affect the pace of wickets and contribute to a root break.
The compatibility of topdressing materials is dependant on many variables, including particle size distribution, shape of particles and soil texture: Materials with a wider particle size distribution will have less porosity and hydraulic conductivity than a material with a narrow particle size distribution (the majority of soil particles having similar size), because more fine soil particles can migrate into the coarse pores of the soil, clogging them, and thus reducing porosity.
The shape of the individual particles will affect the way they perform together, particularly after compaction. Sands that are too angular will 'lock together' causing greater compaction, whereas sands that are too rounded will move against one and other under pressure; shearing delicate roots. Semi-angular or semi-rounded particle shapes are preferable. Soil texture, is the proportion of sand, silt and clay within a rootzone.
It is worth mentioning that sand, silt and clay are classified particle sizes, and therefore closely related to particle size distribution. When buying materials we sometimes choose materials with specific texture ratios (e.g.60: 40 Sand: Soil), this could be used as a means of selecting a suitable material, but there is no guarantee that it is compatible with the existing rootzone. Soil texture also affects the purpose of the topdressing, and therefore the material used.
Heavy clays will benefit from applications of suitable sand, rather than a material with the same properties, to improve the performance of the existing rootzone. Topdressing is one of the main turfgrass maintenance practices, and wherever possible a compatible material should be sourced and used. To ensure that layering doesn't occur within the soil profile, spiking should always be carried out before topdressing, for the 'new' material to be incorporated into the existing rootzone.
To achieve compatibility between topdressings and rootzone, golf greens should whenever possible be top dressed with the same material has the rootzone is composed of. If a previous supplier has vanished and a new supply needed it must be checked to confirm that it is a close a match as possible to the original rootzone mix.
Cricket wickets can suffer from layering if not top-dressed using compatible materials; layers can form because the materials do not 'knit together' and may dry out at different rates causing horizontal breaks, texture breaks and therefore root breaks.
Compatible cricket loams can be checked by a motty test using the existing loam and the proposed one. Motty's should be made of both loams and then cut in half, join one half of the existing loam to one half of the new loam to create a motty of two different halves and allow to dry slowly. Conduct the motty test in the normal way, but look to see where the motty breaks. If it breaks on the interface between the two soils they are not compatible. This is a rule of thumb only, but a good one! Sourcing suitable materials for sports turf is one method by which turf managers and continue to develop quality sports surfaces.
Overall the best method of determining soil properties and compatibility is to have it analysed by a laboratory. This is especially important for new constructions and can be the difference between success and failure.