Ministry of Science &Technology

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Inoculants a fertiliser substitute

Sadly, only half of that tonnage will be on the market said the Director of the Zimbabwe Farmers Union, Mr Paul Zakaria.


 The use of alternatives such as organic fertilizers and inoculants that are cheaper than chemical fertilizers becomes a real option.

Mr Joram Tapfuma the Chief Research Technician of Grasslands Inoculant Factory in Marondera said, Rhizobium Inoculants can serve as an ammonium nitrate alternative to legume growers as they are cheap and easy to use.


“A legume grower with one hectare of soya beans would need between 200-300 kgs of ammonium nitrate fertilizer while on the same piece of land only an 80g sachet of Rhizobium Inoculant  costing US$10.00 is required,” said a legume grower Mr Benny Mangoto.


Rhizobium Inoculants are a specific group of bacteria that have nitrogen fixing characteristics to the soil.

Different types of plants that already have an element of nitrogen fixing are usually referred to as legumes.

Legume plants include grains such as beans, lentils, peanuts and cowpeas while lucerne, clover and stylo are in the pasture legume category.


Nitrogen is an essential element for plant growth.

All legumes and non legumes require the element nitrogen to form chlorophyll and manufacture proteins and other complex compounds within the plant.

Most Zimbabwean soils are deficient in nitrogen because of leaching and growing the same crop seasonally.


There are different types of inoculants that are applied to different legumes.

The rate of bacteria multiplication and reaction to the alkalinity of plants are some of the characteristics that determine the difference in Rhizobium Inoculants.

For this reason, the application of soya beans inoculant to sugar beans will not be effective at all.


In Zimbabwe, Rhizobium Inoculants are manufactured at the Legume Inoculant Factory in Marondera.

“The factory has the capacity to produce a minimum of 70 000 units per year and we are able to meet the legume growers demand at any given time,” said Mr Tapfuma.

He said the only problem the factory is facing is the distribution of the inoculants.


Rhizobium Inoculants can be purchased from Agritex offices, district offices and agro dealers country wide.


Before the production of inoculants begins, bacteria is extracted from live plants or imported.

The bacteria is cultured so that it multiplies before being tested for quality and its characteristics.

The effective bacteria known as the mother culture is inoculated into a sucrose broth containing micro-nutrients then bubbled for four days.

The solution now called rhizobium inoculant is then injected into the sachet and placed in an incubator for 14 days at 28 degrees celsius to enable multiplication of bacteria.

The packets are then randomly selected from each batch and tested for quality control before sale. 

The extraction of nitrogen fixing bacteria from live plants without contaminating it with other forms of bacteria makes it very difficult for farmers to manufacture their own inoculants.


The application of inoculants has always been an issue with farmers.

Mr Tapfuma said inoculants are easy to apply.

“For soya bean inoculant, add 10 teaspoons of sugar to one liter of water mixed with 80g of inoculants. After mixing, spread the seeds on a clean plastic sheet and sprinkle them with the mix until they are all shinny.”

The sugar solution is meant for bacteria to stick onto the seed.


This process should be done under a shade to protect the bacteria from sunlight.


The use of inoculants has been on the increase since the year 2000.

Mr Tapfuma said during the farming season of 2000 and 2001, a total of 232 growers purchased inoculants and the number almost doubled in the year 2005 to a total of 447 growers.

The increase in the use of inoculants has not only been attributed to their affordability but also their ability to increase yields.


Mr Robert Williams a legume commercial grower since 1960, said inoculants had proved to be the most effective means to increase yields,

 “Without inoculants one hectare of soya beans usually yields two tonnes only while the harvest rises up to four tonnes after applying inoculants.”


When inoculants are used for over three years, the soil becomes rich in bacteria to the extent that there will be no need for inoculation the following year.


Unlike fertilizers, inoculants are not affected by leaching caused by excessive moisture.


Since inoculants are a live product, they have to be handled with care.

Planting of inoculants should take place immediately after inoculation under protection from direct sunlight

“The only problem with inoculants is preserving them during transportation to the farm because of the shift in temperatures,” said grower Mangoto.

Inoculants should be protected from temperatures above 30 degrees celsius.


The unfortunate aspect about dead inoculants is that they look just like the live ones.


For inoculants to be effective they should be kept in a cool, shaded area before using them.

A number of aspects have to be put into consideration so as to avoid the failure of inoculants.


Mr Tapfuma said inoculants should not be mixed with agro chemicals such as super phosphates as the acidity of the fertilizer would kill the bacteria.


The effectiveness of inoculants can be checked before harvest time so as to determine the yields one can expect.

Usually effective inoculants result in the formation of large nodules which cluster on the primary and upper lateral roots or near the crown.

They also form a reddish pigment inside.

This can be determined by slicing the nodule of the host plant during the early flowering period and noting the nodule colour inside.  

Ineffective nodules are usually white to pale green on the inside.

Another way of checking the effectiveness of legumes is by carefully pulling out the legume out when it is about 10 centimeters tall and checking the nodules on the roots.


The use of inoculants in legume production does not replace the need for adequate amounts of single super phosphates and lime which retains soil fertility.

Other good soil management practices such as weeding, fertilization, irrigation and soil erosion prevention still need to be done despite using inoculants.

Rhizobium inoculants only act as an alternative to ammonium nitrate.


Storage conditions and unavailability of inoculants near the growers has made it difficult for communal legume growers to use them.


Mr Tapfuma said many soya bean growers where ignorant about the use of inoculants and their benefits adding that there was need to extensively educate all legume growers about rhizobium inoculant and their benefits.”


The use of inoculants has proved to be an effective solution to the unaffordability and the fertilizer bulk storage challenges faced by legume growers.


Agriculture is a major contributor to the country’s Gross Domestic Product hence, any anomaly in that sector results in negative ripple effects on the overall performance of the economy.



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