A Guide to Drainage
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SOIL WATER
There are three types of water in soil . ‘ Hygroscopic water ’ surrounds , and is held tightly to the surface of soil particles . It is held so tightly , partly because of electrolytic action , that it is unavailable to plant roots . ‘ Capillary water ’ is held in the spaces between particles and is available to plant roots . ‘ Gravitational water ’ is passing between the particles draining through the soil by gravity . Eventually in a free draining soil this water will be replaced by air .
Before this gravitational water drains away all the pore spaces are full of water and the soil is said to be ‘ saturated ’. If the only water in the soil is the hygroscopic water unavailable to plants the soil is so dry it has reached ‘ wilting point ’. Between these two conditions is the ideal state and the soil is said to be at ‘ field capacity ’.
golf on it ! As soon as a golfer sets foot on a golf green it is compacted a little bit . The more people play golf on it the more it is compacted . When soil is compacted all the particles get squashed together so there are no spaces between them . Particularly since most soil particles are irregular or angular in shape they nestle into each other . It is these spaces which allow water to move through the soil so if there are no spaces there is no drainage . Even if a good piped drainage system has been installed , if the water can ’ t move through the soil to get to the drainage pipes it will not drain . This is why greenkeepers put so much effort into keeping the soil aerated to maintain a more open soil texture .
Thus at field capacity in a well-structured , organic , well aerated soil we have the necessary conditions for healthy plant growth .
Sadly in the case of sportsturf , in spite of the best efforts of groundsmen and greenkeepers to create and maintain these perfect conditions , we go and spoil it all by playing sport on it !
For example golf course drainage , especially of greens , would be much easier if people didn ’ t play
That is why all golf greens should have sign saying “ Please Keep off the Grass ”!
To put it into perspective a 70 / 30 rootzone material will have an infiltration rate of up to 800mm / hour , a normal sandy loam will be as low as 100 , a clay soil only 50 , but a compacted clay soil is virtually nil .
8 Issue 67