It contains equal parts of Calcium (raises the PH) and Sulphur (lowers the PH) which obviously cancel each other out.
Gypsum's influence on heavy soils is excellent but it is slow moving through the soil profile so it is best worked into the soil so its benefits are immediate.
In the first season (if need be) use it twice, spring and autumn then annually after that until you have got the soil where you like it, don't use it with any artificial fertilisers but is fine with animal manures and or compost.
Use it at the rate of 5 kg per m3 for the first year or two if soil is really heavy and then half that rate annually after that, once the soil has improved a maintenance dressing is 1 kg m3 at least every second year.
If used in conjunction with manures and compost the results can be spectacular, you can turn hard claggy sour soil into beautiful deep friable garden in one session.
Be Happy,
Barry.
www.organic-vegetable-garden.net
