Wednesday February 12 2014

Boosting legumes via nitrogen fixers


Most farmers in Uganda and in East Africa focus on cereal and root crops and have gradually abandoned the production of legumes, which they feel are not commercially viable.
To reverse this trend, there are efforts being made to revamp production of legumes such as groundnuts, climbing beans, cow pea and soya beans.
This is through the use of inputs such as rhizobia, which will help in fixing nitrogen in the soil for improved production of the crops.

Best practices
With expertise from Makerere University’s College of Agriculture and Environmental Sciences, this initiative by International Institute of Tropical Agriculture (IITA) supported by Bill and Melinda Gates Foundation aims to disseminate the best practices among smallholder farmers in western, eastern and northern Uganda. A team of scientists will be involved in processing the required input, known as inoculants, through a biological process from the laboratory.

Dr John Baptist Tumuhairwe, a lecturer at the College, says that the inoculants include living organisms in form of bacteria or fungi. Inoculants have an enzyme that breaks down nitrogen into a form that can be utilised by plants.

He explains: “Legume inoculation is the process of introducing commercially prepared sources of rhizobia to promote nitrogen fixation. This is done by applying inoculum directly to the seed prior to planting or directly to the soil during planting. If the crop was previously grown in the field, there is a good chance that the soil already contains the right rhizobial species. However, the native rhizobia found in soil are often less effective in nitrogen fixation potential.”

Coat or sprinkle
A number of legumes grown in Uganda do not have the capacity to produce sufficient nitrogen to sustain the plant.
This is the reason why scientists are producing rhizobia bacteria, which is very specific in fixing nitrogen in legume plants for improved production.

The scientists will extract the rhizobia bacteria from existing root nodules in the soil and multiply them in the laboratory to formulate inoculants with required mineral elements. They will either be in liquid or powder form. This way the farmer can coat seeds before or sprinkle the inoculant in field before planting.
Dr Peter Ebanyat of Makerere University, who is part of the team, says this project is also going on in countries like Nigeria, Rwanda, DR Congo—where a number of farmers are now engaged in growing crops like soya beans and climbing beans using inoculants, thereby realising increased yields.

Hand in hand
In phase II, Uganda is part of the project; the major focus for farmers in the west is climbing beans, in the north is groundnuts (using improved varieties particularly Serenat I and Serenat II), and in the east and some parts of the north, climbing beans and soya beans.

The scientists will work hand in hand with non-governmental organisations that are already engaging farmers in various parts of the country in growing legume crops using inoculant approach technology.

Preliminary field trial and demonstration sites have been set up in Oyam, Pallisa and Kisoro districts, where farmers are tasked to plant the seeds coated with inoculants.
They are encouraged to use this technology because it will improve on their yields leading to better income.

why nitrogen is vital
Approximately 80 per cent of the atmosphere is nitrogen gas (N2). Unfortunately, N2 is unusable by most living organisms. Plants, animals and micro-organisms can die of nitrogen deficiency, surrounded by N2 they cannot use.

All organisms use the ammonia (NH3) form of nitrogen to manufacture amino acids, proteins, nucleic acids and other nitrogen-containing components necessary for life.
Biological nitrogen fixation is the process that changes inert N2 to biologically useful NH3. This process is mediated in nature only by bacteria.

Other plants benefit from nitrogen-fixing bacteria when the bacteria die and release nitrogen to the environment or when the bacteria live in close association with the plant. In legumes and a few other plants, the bacteria live in small growths on the roots called nodules.

Within these nodules, nitrogen fixation is done by the bacteria, and the NH3 produced is absorbed by the plant. Nitrogen fixation by legumes is a partnership between a bacterium and a plant.