Technical Pitchcare Classifieds
Understanding the fundamentals
James Grundy, Senior Technical Manager at Maxwell Amenity, says that adequate water availability is crucial to soil and plant function
Long range forecasts indicate this summer to be a mix of varying degrees of heat and unsettled conditions swapping back and forth between the typical north-south divide. In practice, that is likely to mean periods of hot, dry weather interchanged with significant volumes of rainfall. In both these instances, the primary factor at play for turf managers will be water management; something which is important because water (H2O) is the master variable which governs plant health. Adequate water availability is crucial to plant and soil function, with the key word being adequate.
Excessive H2O
Associated beneficial microorganisms drown in the soil, limiting plant defence and the mineralisation of nutrients for plant uptake. Like ourselves, plants also need to respire. It is commonly understood that plants
photosynthesise taking in carbon dioxide from the atmosphere which is combined with water sourced from the roots, before going on to react with energy from the sun to make plant‐available biological energy in the form of sugar. However, this process requires oxygen to keep all the electrons balanced and the cells healthy.
In the leaves, plants source this oxygen themselves as a bioproduct of the photosynthesis reaction. Root cells, on the other hand, still require oxygen for healthy function but are not capable of generating it themselves via photosynthesis. As a result, plant roots respire oxygen by sourcing it from the air pockets between soil particles. If those particles are full of water, the roots cannot function healthily and the plant suffers from abiotic (environmental) stress.
Deficient H2O
Like people and animals, plants are essentially tubes. Unlike people and animals, plants process water from the bottom up. This water transportation system starts at the roots, transfers into a network of transport pipes called xylem and ends in the leaves, as water escapes into the atmosphere through pores on the leaf surface called stomata. This cycling of water from roots up and into the xylem, and out through the stomata is called evapotranspiration. Evapotranspiration rate is the speed at which this process takes place, the warmer and drier the atmosphere, the faster the evapotranspiration rate.
When evapotranspiration has drawn water out of the soil, through the plant and up into the atmosphere to the extent there is not enough available water in the soil, the water level in the plant falls below the level required for healthy plant function. The result is a number of negative physical effects on the plant.
Wilting: the initial signs of water stress, caused when the turgor (water) pressure in cells falls, leading the cells to collapse and plants to droop, or in the case of grasses to lose the ability to spring back up when walked upon. If the water content falls low enough, the cells will die.
Reduced photosynthesis: lack of water is limited; the plant diverts the available water to all systems, which limits or even stops
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photosynthesis, the process by which the plant creates its own energy to fuel its metabolic processes.
Reduced respiration: as with reduced photosynthesis in the leaves, reduced respiration in the roots leads to the reduction or halt of metabolic processes required for maintaining healthy roots.
Reduced Transpiration: transpiration is the vital process plants rely on to move nutrients and metabolic substances around their bodies utilising water pressure. Without adequate water, this water pressure cannot be maintained and the system slows or halts.
In the soil: beneficial microorganisms are killed or sent into dormancy, water repellency of soil particles or surface material is initiated, limiting the potential for subsequent rewetting of the soil. Nutritional elements and minerals cannot be solubilised into water films for transport into roots.
In both cases, excessive water or deficient water have a number of negative consequences both on the plant and the wider ecosystem within the soil profile. When plants are subjected to abiotic stress, in the form of too much or too little water, this makes them more susceptible to biotic stress in the form of pathogens such as anthracnose disease (Colletotrichum cereal), microdochium patch (Microdochium nivale), brown patch (Rhizoctonia solani), or dollar spot (Sclerotinia homoeocarpa). All of which will be active when heat and humidity are the prevailing conditions.
Of course, given the understanding outlined above, it is worth considering that dry soils around roots, which place stress on plants, can be also accompanied by humid swards and leaf surfaces due to environmental conditions on overcast showery days or, due to lack or inadequate irrigation which favour the activation, infection and proliferation of fungal pathogens.
Practicalities
As we can see, water is vital for a consistently healthy plant. The relevant point for anyone producing a sports turf surface is that a consistent healthy plant is paramount to producing a consistent sporting surface and, as turf managers, it is always worth reminding ourselves that our primary role is to facilitate a surface for play.
There are a number of management factors which promote adequate water management of a sports turf surface conducive to consistent plant health.
• Aeration: minimise and reduce compaction to create air spaces in soil and facilitate more effective surface water penetration and drainage
• Surfactants: wetting agent programmes help to manage soil water. Penetrants overcome water repellency aiding penetration of irrigation and rainwater. Block‐copolymers hold water in the profile making it available to plants
• Monitoring of evapotranspiration levels: a number of services and systems are available to record daily evapotranspiration levels in millimetres of water lost. Hard data on water lost enables calculation of water replacement
• Moisture meters: regular readings from surfaces allows for determination of areas soil water volumes are approaching critical limits. This informs the requirement for water proactively, before the plant shows symptoms of stress
• Irrigation: well serviced and maintain irrigation systems, with manufacturer supplied figures for water application rates in millimetres per minute allows managers to precisely replace water lost via evapotranspiration once moisture meter readings signal that soil water volume is approaching critical levels
• Potassium: potassium regulates the closing response time of leaf stomata in reaction to water loss rates from evapotranspiration. Adequate supply of potassium throughout warm hot periods allows the plant to react faster to water loss, conserving soil water and postpone wilting
• Seaweed: fresh, cold pressed seaweed contains a number of plant beneficial bioactive compounds such as abscisic acid, cytokinins and gibberellic acids which stimulate a plant’s natural defence responses to both abiotic and biotic stress. Application of a liquid, fresh, cold pressed seaweed prior to stress events primes the plant’s responses in readiness, promoting increased tolerance and improved recovery
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