Controlled release nitrogen fertilizers (CRFs) are fertilizer compounds that release, either by design or naturally, their nitrogen (N) content over an extended period of time. CRFs can prevent N losses of N to the atmosphere or water system, both of which have negative environmental consequences by matching, to the extent possible, N supply with crop demand. They can be effective tools to chemically or physically influence the movement and transformation of N in order to reduce losses. The major constraint associated with widespread use of CRFs on food crops is the cost of the commercial products. Therefore, research is needed to develop more cost-effective technology for controlled or slow-release fertilizers.