Many Australian soils have poor structure, as indicated by poor water penetration.
This is especially undesirable in turf situations. Excess sodium content is a primary cause of poor soil structure. It is estimated that at least one-third of Australian soils have excess sodium levels.
When water or rainfall is applied to a soil with a high sodium content, very fine clay particles dispense into the soil and then block the fine pores between the soil particles. The soil becomes dense, restricting the movement of water, air and plant roots. The ability of the turf to take up nutrients is also hampered. In short, the general health and quality of the turf is significantly diminished.
Gypsum has traditionally been used as a means of improving the friability of clay soils by reducing sodium levels. The calcium ions in the gypsum displace the sodium ions from the outside of the clay particles. The sodium can then be washed down through the soil. The calcium helps the clay particles to link up into an organised lattice of particles, resulting in a more "open" soil structure.
However, bulk gypsum must be applied at very high rates - up to 5 tonnes per hectare in heavy clay soils - and it can be difficult and very costly. A further problem with bulk gypsum is that it may take 12 months or more to become effective, because the particle sizes are relatively large. Gypsum particles are commonly about 1mm diameter.