I was very surprised to find the comment that “biological soil fertility options” are problematic because they “require considerable labour and skill inputs, as well as large volumes of biomass,” and no mention whatsoever of “green manure/cover crops (gm/cc).”  The disconnect between people talking at the international level, and what is going on in the fields of resource-poor farmers in Latin America, Africa and Asia continues to be…well, frightening.

Green manure/cover crop systems do vary greatly around the world and around Africa, depending on climate, basic cropping systems, land tenure and dietary preferences, among other things.  Yet they are already widely practiced by resource-poor farmers, in Africa as well as the other continents.  I have personally stumbled across some 85 such systems spread across over 40 nations.  In one case I researched a single system that is practiced among perhaps 50,000 farmers from Honduras through Guatemala and Belize to Mexico.  Hundreds of thousands of farmers, if not millions, use similar systems in South America and Southeast Asia, and other hundreds of thousands in each of a dozen nations of Africa, at least.

Many gm/cc systems reduce farmers’ labour, because when the gm/cc is intercropped with cash or subsistence crops, they often control the weeds, thereby eliminating one or more of the farmers’ (usually women’s) weeding operations.  Thus, the assumption that these systems necessarily require added labour is just plain wrong.  It is true that improving soils dramatically (ie doubling or tripling low traditional levels of productivity) requires large amounts of biomass, but that this factor is listed as a problem of biological options is wrong because the gm/cc species produce that biomass in the field (often 40 to 70 t/ha, green weight), at very little cost.  In fact, in many, if not most, of the adopted gm/cc systems around the world, the beans, peas or other food or fodder produced by the gm/cc is much more valuable than the labour and costs occasioned by the practice.  That is, the net cost/value of the biomass produced for soil improvement (that biomass not going to either the market or the family table) is negative.

The skill inputs needed by the top agronomists in a country may be fairly large, but for any single farmer or village of farmers they are rarely much more than those required to use inorganic fertilizers efficiently.

To respond, then, to your question about inorganics being the best entry, my response is that, in the vast majority of cases, they are not the best.  If the soil still has enough natural fertility to grow weeds, farmers can grow green manure/cover crops along with their regular crops, as improved fallows, on “wastelands,” or in other niches that don’t have any opportunity cost.  Such a technology requires an investment of a few pennies to buy the original gm/cc seed, and within a year (or sometimes two) can make a major improvement in the farmers’ productivity, soil water retention, infiltration of water, crop root growth, resistance to termite damage, resistance to erosion, soil organic matter content, nitrogen content, etc.  Inorganic fertilizers may supplement the gm/cc (especially to provide replacement phosphorus, plus nitrogen when there are problems of synchronisation), but these applications would usually be in much smaller quantities than conventional agronomists would recommend.

Roland Bunch, former member
UN Millennium Project Task Force on Hunger
rolandbunchw@yahoo.com