Simple way to boost the fertility of your soil using bacteria

Farmers plant maize and beans in Nandi County using chemical fertiliser. Rhizobia can easily be applied on the farm. FILE PHOTO |

What you need to know:

  • Bio-fertilisers have the potential of increasing yields of legumes as well as reducing the use and cost of nitrogen-fixing chemical fertilisers.
  • When rhizobia are present and nitrogen is being fixed, nodules can be seen on the roots of the plants.
  • The rhizobia population declines over time, even under proper storage conditions.

Lack of nitrogen in the soil is a key limiting factor in crop production. 

Many farmers, therefore, regularly seek ways to boost the key mineral in the soil.

Most of them, however, turn to chemical fertilisers such as DAP, CAN and urea to supply nitrogen.

Sadly, this has complicated the problem by contributing to soil acidification as farmers spend a lot of cash on the inputs.

However, instead of relying on chemical fertilisers, bio-fertilisers containing rhizobia can help legume plants extract nitrogen from the air and convert it into forms they can easily use, thus, achieving higher yields.

Rhizobia inoculants are live bacteria cultures that are applied on seeds or young plants, helping their root systems get beneficial bacteria. Using inoculants ensures that the plants receive the best rhizobium strain for optimum growth.

Bio-fertilisers have the potential of increasing yields of legumes as well as reducing the use and cost of nitrogen-fixing chemical fertilisers.

In Kenya, the MIRCEN project at the University of Nairobi has since 1981 developed a rhizobium inoculant known as Biofix and is available in the local market. Biofix is an attractive technology because it is much cheaper than inorganic nitrogen fertilisers.

It is sold in small packs of 50 grams, which go for as low as Sh180. Only 100 grams of Biofix are required to inoculate 10kg of bean seeds for an acre, compared to conventional topdressing fertiliser, which one requires 125kg for the same piece of land.

Furthermore, bio-fertilisers are lighter to transport, require less labour for application and are environment friendly.

How is inoculant applied?

Inoculation means infecting the plant roots with the rhizobia. Rhizobia inoculant can be applied on seeds or young plants. Usually, rhizobium bacteria come in a peat-based inoculant, with billions of cells per gram. The inoculant is usually coated on the seed immediately before planting, or dispersed in clean water or soaked into the planting medium.

Some 100 grams of inoculant is usually sufficient for 20,000 to 100,000 seeds. The cost is negligible per plant. A small portion of inoculants replace huge amounts of nitrogen fertiliser in the life of the plant.

Selecting correct inoculant

Each legume requires a specific species and strain of rhizobia. For example, the rhizobial species that nodulates soybean will not nodulate dry beans.
When selecting inoculum, consult your supplier and read the packaging label to be sure you select the correct inoculum for the crop.

Verifying the effectiveness of inoculation

When rhizobia are present and nitrogen is being fixed, nodules can be seen on the roots of the plants. Each of the nodules houses millions of rhizobia bacteria. When a nodule is opened, pink or red colour seen inside is a good indicator that it is active; that biological nitrogen-fixation is taking place.

Thus, the effectiveness of inoculation can be verified easily with the naked eye. The rhizobia will survive and multiply as the plant grows.

Storage of inoculum

Inoculum contains living rhizobial cells that survive on an organic carrier such as peat. The rhizobia population declines over time, even under proper storage conditions. Most inoculum manufacturers put an expiry date on the package. Do not purchase expired inoculants. The rhizobial population decline significantly after the expiry date.

Purchase only the amount of inoculum or pre-inoculated seeds needed for one planting season.

When treating seeds on the farm, avoid applying the bio-fertiliser on more than those you can plant in a day. Inoculant packages provide information regarding the amount of seeds that can be treated with a measured amount of inoculum.

Farmers should take advantage of this technology and improve their yields while saving on cost of production and taking care of the environment.

Korir works in the Department of Crops, Horticulture and soils, Egerton University