Comparison of Cyanobacterial Bio-Fertilizer With Urea On Two Soils and Three Crops.

Fertilizer use in Ethiopia is low, and crop yields and malnutrition rates reflect this low usage rate.  Urea is too expensive for most farmers, and compost supplies are inadequate.  A locally-produced bio-fertilizer produced by harnessing cyanobacteria could help bridge this gap.  Objectives of this study were to compare the impact of cyanobacterial fertilizer cultured from Ethiopian soils (Anabaena sp.) with urea applied to two soils (an acidic Alfisol and an alkaline Andosol) at the same N rate and to evaluate their impacts on soil properties, plant growth, and plant nutrient concentrations on kale (Brassica carinata L.), hot pepper (Capsicum annuum L.), and maize (Zea mays L.).  Each experiment included a factorial combination of four nitrogen fertilizer sources (control, urea, dried cyanobacteria, and liquid cyanobacteria,) and two soil types arranged in a complete randomized design.  Anabaena sp. were cultured from Ethiopian soils and grown in aerated 400-L ponds inside a hoop house.  Cyanobacteria were harvested after 21 d of growth and utilized as either liquid (42 mg N L^-1) or air-dried (3.0 % N) fertilizers.  Fertilizers were applied at the same N rates within each study based on crop-specific N recommendations from the Ethiopian government.  The cyanobacterial bio-fertilizer treatments consistently increased soil organic C concentration.  Although fertilizer treatments were applied at the same N rate, the final total N concentration in the soil was higher in the cyanobacterial treatments as compared to urea.  This could be due to higher volatilization of NH₃ and N₂O from urea or continuing N fixation by the cyanobacteria.  The dry cyanobacterial bio-fertilizer resulted in the highest plant N concentrations, plant height, and shoot dry weight for all three crops.  Overall, the plants receiving dry cyanobacteria grew better than those fertilized with liquid cyanobacteria or urea, even though they were applied at the same N rate.