Q: How do inorganic fertilisers damage soil?
A: Plants need ammonium as a source of nitrogen to be taken up in various forms. Ammonium is ammonium irrespective of source i.e. the plant cannot tell the difference if it is sourced naturally from nitrogen fixing bacteria or waste from nematodes or worms or from ammonium nitrate or sulphate in a fertiliser bag. This is why you can get excellent short term results with inorganic fertilisers. However inorganic fertilisers are mineral salts and there is a limit to the amount of salts that you can put into the soil before you start to kill off soil biology. Plus if the plant is sitting in a sea of nutrient it does not form the associations with mycorrhizae and other microbes that it needs to access nutrient naturally.
Q: My soil is heavy clay what can I do to improve it?
A: The fastest way to improve clay soil is to work sand into the top layer and then apply 2” (5cm) of aerobic compost over the surface followed by 1” -2.5cm a year thereafter. For lawns apply ½” or 1cm per year and brush it in or apply in several applications. If you are growing vegetables you can move your potato patch around the plot as the massive concentration of soil biology they support will break up the soil. If this is too much hard work put in some raised beds and fill with compost rich soil the clay underneath will slowly break down.
Q: I want to reduce the soil Ph what is the best way?
A: Biological degradation of organic matter produces a wide range of organic acids like humic and fulvic acid, after a year or so of developing healthy soil your pH will be suitable for most plants. If you want to grow acid loving plants like camellias or rhododendrons you can apply a small amount of ferrous sulphate for a quick hit but in the long term it is better to apply ericaceous compost or if you can source them make your own compost with pine needles.