Here's another study about managing soil carbon loss in biofuel production.

. . . scientists from Michigan State University report on the effectiveness of carbon augmentation practices, including the integration of cover crops, manure, and compost, to supplant carbon loss in corn stover removed cropping systems. The results indicate that corn stover based bioenergy cropping systems can be managed to increase short-term carbon sequestration rates and reduce overall net global warming potential by using no-till planting methods and a manure-based nutrient management system.

The research team measured soil carbon changes as well as nitrous oxide and methane gas emissions from corn stover-ethanol field plots managed under various carbon augmentation practices. In addition to the gas emissions measured in the field, other carbon emissions assessed included estimates for the manufacturing carbon cost of crop inputs; methane emissions from the livestock manure source; methane and nitrous oxides generated during manure storage and application; and the fuel used in crop production and in gathering and land applying the manure.

"These results show that bioenergy cropping systems, particularly those integrating livestock manure into their management scheme, are a win-win option on both alternative energy and environmental fronts," says Kurt Thelen, member of the research team.

But, where does the manure and compost come from? What land is impoverished in order to jigger the numbers on fields stripped of stover? This is a thumb-on-the-scales type of argument that achieves its seemingly positive outcomes by bounding the system in a way to exclude negative externalities.

A more sensible system would wind-row the stover and graze it in place. This would provide manure as well as producing more food while increasing soil carbon. Cover cropping in fallow periods and no-till sowing are good ideas too, but they should be done in any case.

I can appreciate the effort to reduce the harms of biofuel production but they are somewhat improved practices that could be used whether the crops are stripped for biofuel production or not. Such studies need to go further and consider the opportunity costs of imported carbon from composts and manures, and also establish that these imports are available in large enough quantities to matter.