Biofuels, cellulosic ethanol hard on soils
July 18th, 2008 by Jim JustPublic support for biofuels is costly and has little impact in cutting greenhouse gas emissions. Biofuels also cause high environmental risks, particularly in Latin America and large parts of Africa, and are causing food prices to skyrocket around the world.
So says the EU’s Organization for Economic Co-operation and Development. Governments are are increasingly doubtful about whether biofuels were as “green” as they claim to be when taking account of the total energy needed to produce them and the environmental impact of intensive farming and increased land use. Governments would do better promoting lower energy consumption to fight climate change.
Ron Steenblick at Gristmill writes that converting crop residues into cellulosic ethanol isn’t such a good idea, either. According to respected USDA soil scientist Ann Kennedy, the stems and leaves left over after crops are harvested may have more value if they are left on the ground – especially in areas receiving less than 25 inches of rainfall per year.
Kennedy explains in an article at Science Daily that organic matter provides nutrients crops need, helps the soil hold water and contributes to the formation of soil clods that help prevent wind erosion. The percentage of organic matter in a given soil varies naturally from region to region, depending on climate, soil disturbance, moisture and vegetation. Generally speaking, more moisture leads to more vegetation, which is the feedstock for the microbes that break down residue into organic matter.
Where no-till or one-till systems are employed, at least a ton of residue per acre per year is needed to build soil organic matter over time. In fields with multiple tillage passes, organic matter may not increase even if all the drop residue is left in the field. Kennedy thinks multiple tillage may mix the soil and residue too well, in essence over-feeding the microbes. The microbes consume the incorporated residue too quickly, releasing most of it into the air as carbon dioxide.
If residue were harvested, soil fertility would drop and farmers would have to find other ways to increase the amount of organic matter in their soils.
Kennedy cautions:
“We need to constantly replenish organic matter—so removing valuable residue, especially in areas with low rainfall, may not be the best practice.”