3. Effects on food production – There are millons of people in the world who do not have enough food to eat, the conversion of land from food crops to energy crops presents ethical issue. The use of crop residues and animal waste as a source of energy also presents some problem. These materials supply an important source of organic matter and soil nutrients for farmers. This is particularly true among subsistence farmers in developing world. They cannot afford fertilizer and rely on these materials to maintain soil fertility. However, they also need energy. Thus, they must make difficult decisions about how to use this biomass resource.