There is a lot of discussion about superphosphate, but we have found it is essential to stimulate the native grasses, along with some clover, to produce a bulk of feed initially. The sheep then spread the manure and fertility, and overtime, a build-up of humous occurs. Ideally we then add the phosphorous via the animal, by always having a mineral lick out for the sheep. Every time an animal leaves the farm it takes with it a bucket of minerals, and these need to be replaced! We sowed a very poor paddock with sub clover and left it ungrazed for a year, the hayed off clover made a layer of organic matter and the soil was much spongier after this time. I have heard people say that "super" makes soil more acid, but believe that it is apparently the legumes conversion of the nitrogen to an available form for the plants, that causes the acidity.