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TECHNICAL


Fig. 7: LV20 & LV25 sand PSD graphs


agronomical, that high inputs of sand can have. Wear and tear on machinery and cutting units can put pressure on budgets, particularly when in-house grinding is not an option. High annual application targets can eat into labour demands when staffing numbers are limited. From an agronomy point, the potential adverse impact that high application rates can have on disease pressure is one that Scott gives careful consideration to. Reduced available leaf blade exposure to sunlight, surface pH fluctuations and uneven leaf blade incision from blunt cutting units will all contribute to putting the grass plant under increased stress, making it less able to fend off attacks from harmful pathogens.


Fig. 8: Aggregate formation on root hairs


Material cost and consistency is also an area Scott believes to be problematic. With the abundance of sand reducing globally, whilst demand and carriage costs increase, these issues will only continue to manifest themselves in an upward trajectory, one which is outwith your control. Scott also includes a biological element as part of his maintenance programme. As well as the addition of organic acids such as humic and fulvic acids, compost teas are applied monthly over a ten month period. This again being an example of biological inputs playing a pivotal role.


Fig. 9: Biologically active profile showing high level of OM humification ©SYMBIO 2019


142 PC October/November 2019


The use of the Leavenseat LV20 and LV25 by Scott and Jim provides a good opportunity to quickly highlight the relevance that PSD can have depending on the objective. Due to the fact that the top layer of the profile at BT Murrayfield is being replaced on an annual basis, Jim has less concerns regarding the migration of fine particles over time. As can be seen in Fig. 7, the LV25 has a more uniform PSD with 35.9% falling within the fine/very fine category compared to 17.3% of the LV20. Whilst the coarseness of the LV20 may bring with it some issues for Scott in respect of working the topdressing into the sward and wear on cutting units, it minimizes the potential of ‘capping’ issues in the profile. This situation occurs when fine particles ‘interpack’ and ‘bridge’ the pore spaces created by coarser particles, this hindering the free movement of water. If allowed to develop over a period of time due to


incompatible rootzone/topdressing materials, this can have drastic consequences on turf performance, particularly in golf greens. The use of material PSD data sheets and ‘D’ value graphs should always be used to guard against this.


You may well have noticed a common thread forming in the article with regards sand and soil biology. The dependable attributes that make sand beneficial can also prove to be problematic in a growing medium, with its simplicity and inert nature being both an asset and a liability. An area I will attempt to expand on next.


When evaluating any growing medium, it is important to recognise it as a living entity, a continually evolving dynamic of inputs and outputs, nutrients and energy, providing you with a foundation to manipulate for your individual requirements. The value of aggregate formation is now increasingly recognised in the agriculture sector for maintaining the long term health of a soil. The macro and micro pores that are created by soil aggregates are recognised as the biological reactors for the multitude of microbial processes that underpin the health of a soil (Fig. 8). Agriculture has learned the hard way, with an over reliance on synthetic fertilisers for crop nutrition resulting in infertile soils lacking in OM and structure, which are prone to erosion.


This shift in mindset has led to a term referred to as ‘light farming’, which recognises the benefits of harnessing the energy of solar radiation through photosynthesis. This approach enables atmospheric Carbon (C) to be incorporated into the biomass of plant material through the process of fixation. Increased emphasis on organic nutrient inputs (slurry, crop residues, legume cover crops, rotation cycles) has enhanced subsequent soil C levels through OM decomposition and liquid C root exudates. This availability of organic C is a source of energy to soil microbes and crucial to particle bonding, allowing aggregate formation.


Can the turf industry learn from agriculture?


Well, something similar is already possible through utilising biological programmes.


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