How farmer uses bio-digester to tackle soil acidity

Joseph Tanui, a farmer in Kapseret in Uasin Gishu County, at his vegetable farm
Joseph Tanui, a farmer in Kapseret in Uasin Gishu County, at his vegetable farm. PHOTO | LEOPOLD OBI | NMG 

In the country’s rural villages, tens of farmers are purposely embracing bioslurry - a liquid discharge from biodigesters after gas has been tapped for energy – to nourish the soil.

Rising soil acidity across many farms is dealing heavy blows to crop yields that keep dwindling by the season.

Soil analysis conducted across farms in 25 counties in 2014 revealed high acidity levels far beyond the acceptable limit.

The research found the soil pH in breadbasket counties such as Uasin Gishu, Nandi, Trans-Nzoia and Bungoma to be quite low, hence acidic. Soil from the Uasin Gishu County for instance, measured between extremely acidic (4.35 pH) to slightly acidic (6.36 pH) on the chemical pH scale. Soils with such levels of acidity are unsuitable for farming.

The Kenya Agricultural and Livestock Research Organisation (Kalro), which conducted the analysis, linked the acidity to over use of inorganic fertilisers, particularly Diammonium phosphate or DAP. It recommended soil specific fertilisers to mitigate the crisis.


Also recommended was the use of liming materials to neutralise the acidity. Unfortunately, only a few smallholder farmers can afford the process, as a tonne of lime costs over Sh4,000.

Some farmers are using the by-products from bio-gas producing biodigesters as an alternative method of enhancing their farms productivity.

Joseph Tanui, a farmer in Kipreset in Uasin Gishu County, is one of those who is finding biodigesters useful. Tanui grows Boma Rhodes grass on a two-acre plot and vegetables on a quarter acre.

He explained that he collects fresh cow dung from his neighbours which he supplements with those from his own two cows to feed his biogas plant.

To make a bioslurry water and cow dung and mixed in a 1:1 ratio then left to ferment.

During the fermentation natural microorganisms break down the manure to produce biogas (in the form of methane gas). Another by-product is, compost, which adds humus in the soil.

Researchers say that if the methane gas is not captured through biogas production, a lot of it ends up in the atmosphere where it damages the ozone layer leading to global warming.

Kevin Kinisu, Kenya Biogas Programme country manager, points out that more than 22,000 households in the country have adopted the technology, sequestering over 417,000 tonnes equivalent of carbon emissions per year and contributing to prevention of deforestation of over 34,000 hectares of forest – about 34 times the size of Karura forest in Nairobi.

Kenya Biogas Programme estimates that there are more than 100,000 people in the country have installed biodigesters as biogas plants in their homes. Among the main uses are energy production and bioslurry fertiliser production. Others, like Tanui, also use the sludge as a natural pesticide against farm pests like aphids.

The technology is gaining ground faster in Kenya than in any other African country. The country’s biogas sector has attracted six companies that are all successfully deploying prefabricated systems. Over 140 entrepreneurs are at work constructing fixed dome masonry-type bio digesters.

The technology’s biggest challenge is affordability. Tanui, for instance, bought his digester in 2013 at Sh150,000 using a bank loan. Luckily, he was able to repay the loan within a few months from proceeds from the Boma Rhodes sale.