Gradation Index 
This is often abbreviated to G.I. and is a numerical value based which identifies the uniformity of sand particles in a sample of sieved soil. A G.I. value is a ratio of the larger to smaller diameter particles and is based on the selected D values used. A uniform sand reduces the potential for the particles to be compacted, with a more open pore space being able to be retained, improving drainage and root growth potential. The lower the G.I. value the more uniform the particles and the more suitable they are for sports turf situations. A larger G.I. value will see much more interpacking of th
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Gradient [1]
A slope. It might be an incline (going uphill) or a decline (going downhill). A gradient is typically expressed either as a ratio, for example 1 in 100, or as a percentage, for example a 1% gradient. Each of these examples mean that there is a 1-unit difference over 100 units; so over 100m this will mean a difference in height of 1m. Also called a Fall or Slope.
Grading
The action of moving soil around to achieve desired levels of uniform evenness.
There are two main techniques used in grading:
1. Cut and Fill Technique
2. Strip and Replace Technique
Granular
A soil ped, which is sub-divided into Granular and Crumb, having rounded surfaces and is common in topsoil (A Horizons). A Granular structure is relatively small and compact within an aggregate, being less porous than a Crumb structure which is more porous, and this is represented by a good topsoil that has good organic matter content and an active soil fauna and micro-organisms. This is the best structure for most soils, especially turfculture.
Gravel
Small to large stones. Gravel is a material with a diameter between 2 and 64mm. It is categorised using the Udden-Wentworth scale as granular gravel (2 to 4mm diameter) and pebble gravel (4 to 64mm diameter).
Gravel Raft
A layer of free draining material usually gravel or stone, about 100 to 150mm in depth. It is sometimes installed on specially constructed sports pitches beneath the root zone material, being separated from this by a blinding layer. This may also be referred to as a Drainage Raft or just a Raft.
Gravitational Water
Excess water within a soil which will drain away and which is unavailable for use by a plant. It is water which is temporarily present between the states of Field Capacity and Saturation Point.
Grid Drainage
A drainage system where the lateral drainage trenches and pipes are in a grid like pattern, being parallel to each other. They will typically join perimeter drains at 90 degrees. This is also called grid iron or parallel drainage.
Groundwater
All water which is stored below the ground in rocks or other geological strata. The water within a water table can be classed as ground water. A formal definition is, 'All water which is below the surface of the ground and in direct contact with the ground or subsoil'; Flood and Water Management Act 2010 (S5 (4)).
Growing Medium