Why do you have lawns that are hard?
/Essentially it is because there is poor Soil Biology present in the soil. 50% of a healthy soil is air. Soil with poor Soil Biology are compacted and hard.
This can be rectified, as a first step we can drench with a liquid that naturally aerates the soil, we can then drench with a Compost Tea that includes all of the good parts of the Soil Food Web apart from worms and insects. Then we can introduce worms to achieve the estimated requirement of 20/m2.
One application could be sufficient, but 6 weekly applications during the growing season can be applied.
A more direct approach is to decompate using Air Probes to deliver blasts of air at depths down to 1 metre to create fissures in the soil. These are kept open by an injection of a natural material Terramol and mineral zeolites (micro porous habitats for microbes containing 9 types of Myccorhizal Fungi and 16 of the most benefical soil bacteria.
Once the Soil Biology is present, it needs to be feed, it will get some food from the roots the Myccorhizal Fungi are attached to. Ideally mulching mowers should be used that return the grass clippings to the base of the grass, where it is consumed by the Soil Biology.
When aiming to have optium Soil Biology, man made fertilisers should not be used as these degrade Soil Biology.