Exploring the Potential for Cyanobacterial Nitrogen Fertilizer to Improve Soil Fertility in Ethiopia.

Soil fertility degradation and limited access to fertilizer are key constraints to smallholder agriculture, especially in Africa where fertilizer use rates are the lowest in the world.  Most agricultural soils in Ethiopia are deficient in N, and Ethiopia is among those African countries with the highest rates (≥ 40 kg N/ha/yr) of nutrient depletion. The goal of this project is to develop a system that smallholder farmers can use to make their own N fertilizer, thus providing access to a key agricultural input without dependence on expensive fertilizer imports or costly transportation over poor roads.  To achieve this goal, we are evaluating the potential for cultivation of N-fixing cyanobacteria in shallow ponds for application to crops as a N fertilizer.  Interviews of Ethiopian farmers have been conducted to assess their interest and constraints in utilizing an on-farm cyanobacteria production system.  Eleven percent of Ethiopia’s land area is made up of Vertisols, which may be ideal for minimizing the cost for lining ponds.  Soil samples were collected from inundated areas of Colorado and Ethiopia. Cyanobacteria were cultivated from these soils using two methods:  inoculation into aerated N-free Allen-Arnon media and construction of Winogradsky columns.  In general, the Allen-Arnon media has been found to facilitate growth of filamentous heterocystous cyanobacteria, while unicellular cyanobacteria have flourished in the Winogradsky columns.  Studies in aquariums have demonstrated the importance of aeration for optimizing N fixation.  The impact of nutrient concentrations (particularly Fe and Mo) on cyanobacterial growth rates and N fixation quantities is being measured in a replicated batch experiment.  Evaluation of locally appropriate and affordable means to aerate ponds and supply nutrients is a critical step towards feasibility of such a system.  Application of cyanobacteria as fertilizer will also enrich soil C levels, leading to improved soil quality and increased crop yields.