Try biosolids and wood. Treated biosolids and wood materials Sawdust, wood chips, and sewage sludge (which are pre-treated before using as fertilizer) all contain nitrogen and can all be used in nitrogen fertilizers, just make sure that the biosolid you will be using are treated and monitored properly, if not,the associated risks of such products may not be worth the potential benefit. Moreover, because these materials all decompose slowly and contribute small amounts of nitrogen, they are not even the most beneficial nitrogen components available.While they might not be the best choice for nitrogen fertilizers, biosolid fertilizers add much needed nutrients. Wood chips also add anchorage for the plant