Most gardeners are nuts about organic matter.
You want organic matter to do two contrasting things. On the one hand you want it to persist in soil so that it makes a sandy soil hold more water and makes clayey soil more friable. On the other hand, you don't want it to persist - you want it to break down to supply nutrients to plants, especially nitrogen. So contrasting kinds of organic matter can both be good - but for opposite reasons and serve different functions. Before looking at the various kinds of organic matter, we need to consider the effects of organic matter on pH. There can be two effects of organic matter on pH - direct and indirect.