Nitrogen supply is a key limiting ingredient in crop production in many African countries. It is often not available and/or beyond the reach of many poor farmers, especially those in rural areas. However, biological nitrogen fixation (BNF), the fixing of atmospheric nitrogen by microbes and making it available to plants, could be harnessed to improve the soil fertility and productivity of crops (Mekonnen et al., 2002). These microorganisms are often referred to as biofertilizers. However, biofertilizers also include microorganisms that solubilize phosphorus to make it available for plants (Garg et al., 2001).
Many microorganisms have the ability to fix nitrogen. These include Azospirillum, Azotobacter, Rhizobium, Sesbania, algae and Mycorrhizae, while P. striata, and B. megaterium and Aspergillus are among other microorganisms that solubilize phosphorus. In return, the plant provides these organisms with a favourable habitat and a carbon source in a symbiotic relationship. It is this relationship that is critical in seeking to broaden the use of biofertilizers in association with many food crops. Biofertilizers have been used in Kenya, the United Republic of Tanzania, Zambia
and Zimbabwe (Juma and Konde, 2002). They are easily produced locally and the technology needed to produce them is not complex. In some countries, the demand has often outstripped production of the pilot plants. Expansion of these pilot plants could help improve food productivity in Africa.
The use of biopesticides in the control of pests is well established. For example, sterile tsetse flies (the vector of sleeping sickness) were used to control and eliminate the tsetse fly population on the island of Zanzibar. Similarly, the cassava mealybug, Phenacoccus manihoti, was effectively controlled using a wasp, Apoanagyrus lopezi, from Latin America, and this work was awarded the World Food Prize. The bacteria Bacillus thuringiensis (Bt) has been used by farmers to control worms and insects for many years. Nematodes, bacteria, fungi and viruses may be used to control industrial, home and farm pests.
On a large scale, the use of biopesticides has remained small, representing only a small fraction of the global $8 billion pesticide market. Bacillus thuringiensis (Bt) alone accounts for 90% of the $160 million biopesticides market (Jarvis, 2000). The biopesticide market is driven by consumer, retail and government demands for reduction in use of chemical fertilizer use. The limiting factors include lack of spectrum (few targets), slow killing rate, batch variations, high sensitivity (to soil types, chemicals, temperature and moisture content) and low stability (short shelflife and high storage needs).
