1. Biomass produces greenhouse emissions. The biggest argument against biomass is that it produces carbon dioxide and other greenhouse gases.
2. It takes more energy to plant ,cultivate and harvest the crops and trees than it is worth to get a net energy gain. It also takes up more water from the earth and other fossil fuels to make the fertilizers and fuels for planting and harvesting. it also, supposedly, takes up more land for the crops and tree.3.Biomass collection is difficult.
4. Biomass crops not available all year. Corn, wheat, barley and the like are seasonal crops. They are not available all year. Trees are also a slow growing resource even though they are renewable. This would also tend to be a negative on the side of biomass fuels.