Football Focus Issue 68 | Page 7

A Guide to Drainage
SOIL TEXTURE and PERMEABLITY
Ideally an additional component in the solid portion of soil is organic matter made up of humus , roots , and organisms . This organic matter is usually only as little as 5 % but it is important to give soil a structure by helping particles to clump together to form crumbs of various sizes .
The size of the spaces between these particles and crumbs , the pore space , is fundamental to the ability of a soil to either hold water or drain freely . Clay soils with lots of small pores are said to have a high porosity which means it will hold a lot of water , a more loamy soil with good organic matter will have fewer and larger pore spaces , a lower porosity , and will hold onto less water . The clay soils with small pore spaces also hold the water more tightly which means they are less permeable and drain less freely . This is why they can more easily become waterlogged . Soils with larger pore spaces , like sand , are more permeable and drain more freely .
SOIL WATER SYSTEM
The ‘ Soil Water System ’ introduces water to soil from rainfall . When rainfall hits the ground several things can happen to it . Some can be evaporated from the soil surface straight back up into the atmosphere . Some will run off the surface into a stream , watercourse or ditch . Some will be absorbed into the soil to be taken up by plant roots and released back to the atmosphere through transpiration of the plants be they grass , crops , or trees .
Rainfall will also be absorbed into the upper layers of the soil profile to become ‘ soil water ’. Beneath this upper layer water will percolate by gravity through an intermediate zone into soil at a deeper level where it becomes ‘ groundwater ’. The top of this groundwater level is the ‘ water table ’. The level of this water table can vary depending on the soil profile including type and depth of top soil , type of subsoil , and presence of any impermeable layers .
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