Within weeks we will be watering
(Turf Business, March/April 2008)
Grass turfed areas are saturated – after the driest February in years good rains in March have recharged shallow reservoirs in sandy rootzones. Yet within weeks this limited water storage will be quickly lost by increasing evapotranspiration (ET). Dry patches will become apparent and irrigation will commence. There should be an endeavour to barely maintain adequate water storage in the upper 75mm of the rootzone. To achieve this, the following simple steps can be invaluable:
- Knowing the range of ET expected on hot days and having an idea of the penetration in millimeters applied with each irrigation cycle – as well as keeping account of the measurement of ‘effective’ rainfall that actually penetrates and is not lost by run-off – gives peace of mind in the water status to the depth of the roots.
- Calculations of the water balance only give an idea in the basic condition. Within a green varying soil conditions, high or low points, shady or exposed areas can only be judged by frequent daily probing. If the soil probed to 75mm wets the hands there is too much water present but if the soil flows like salt grass cover could suffer soon.
- In order to get the best value from irrigation systems it is vital they apply water evenly. Nozzles and spacing should be checked and measurement of the uniformity of a sprinkler distribution is the first prerequisite for conserving applied water.
- Short duration repeat irrigation cycles ensure penetration without run-off. Thatch, compaction and gradient all influence water retention and so probing is essential to gauge actual water penetration into the rootzone.
- Hand watering with the aid of tining and the use of wetting agents is the only way to overcome localised dry areas. Increasing irrigation cycles can make the condition worse with run-off from high areas creating excesses in the low areas.
- Remember there is only a reservoir of about 6mm of available water in the rootzone depth of 50mm though this could appear to be nearer 9mm due to the time lag in water penetration and water held in the thatch. With high ET over a few days this reservoir can be quickly depleted.
- Judicious management of the maintenance programme can prolong water storage and reduce the water use rate of turfgrass without impairing the playing surface. The turfgrass plant shows little visual loss in quality with carefully managed deficit irrigation. This simply means applying less water than the theoretical calculated requirement.
- Deep tine aeration to create a porous root zone and deeper roots will mean that more water can be stored to a greater depth. Good nutrition ensuring adequate potassium levels also promotes better durability at the time of water stress and increasing the interval between mowing reduces the rate of water loss.