Biofuel Fertilizer Usage

A common argument against biofuels is that we would still need to produce fertilizer to grow the plant. However, biofuels are made of Carbon, Hydrogen and Oxygen. They do not contain Nitrogen, Phosphorus, Sulfur, Sodium, Magnesium, Potassium, Calcium, Manganese, Iron, Copper, Zinc or Molybdenum, let alone Boron, Chromium, Cobalt, Fluorine, Iodine, or Selenium.

So what fertilizers do we need to add? Surely we just need to recirculate the plant mash back to the soil (possibly via animals) and these elements will not be removed.

Of course, there are other arguments to consider against biofuels.