The next frontier for soil fertility

Monday May 5 2014

Amid grave concerns of Kenya’s rapidly declining soil fertility that is evident in diminishing harvests, a soil scientist has revealed the immense potential that lies in human faecal manure. PHOTO | NATION

Amid grave concerns of Kenya’s rapidly declining soil fertility that is evident in diminishing harvests, a soil scientist has revealed the immense potential that lies in human faecal manure. PHOTO | NATION 

By DOROTHY KWEYU
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Amid grave concerns of Kenya’s rapidly declining soil fertility that is evident in diminishing harvests, a soil scientist has revealed the immense potential that lies in human faecal manure.

And Prof Nancy Karanja of the University of Nairobi’s Land Resource Management and Agricultural Technology (Larmat) Department at the Upper Kabete campus on the outskirts of Nairobi is not fighting a lone battle. Financiers have begun pumping funds into the unlikely resource, inasmuch as it is culturally shunned, to reverse the downward spiral of food production, which is raising serious concern.

On Tuesday, Devolution Cabinet Secretary Ann Waiguru released the 2013 Economic Survey, which cast food security as a big challenge even after the government provided farmers with subsidised fertiliser and other farm inputs.

Maize production, according to the survey, had declined from 39.7 million bags in 2012 to 38.9 million last year.

But that is only part of the story. We can now report that the bigger reason for Kenya’s dwindling harvests is soil depletion that has been accelerating over the years. According to Prof Karanja, synthetic fertilisers, to which Kenyan farmers are hooked, are to largely blame for increased soil acidity, which is contributing to declining maize yields.

Not only that; wheat, maize and sugarcane, the main crops grown in the western Kenya food granary, have been burning organic carbon, which is essential for soil health. “We have no carbon. After 100 years of growing maize in Kitale, you don’t expect to have carbon in the soil.

The ecological processes have collapsed and we have to bring them back,” says the don.

Led by British charity Oxfam GB, which three years ago gave Sh30 million to the Umande Trust, for its bio-sanitation programme that is working with schools and communities to harvest excreta to produce energy and fertilise soil for urban agriculture, a growing number of financiers have been voting for human faecal manure with their funds, providing a major boost to what, until recently, might have been described as mere curiosity by soil scientists.

During a recent interview, Prof Karanja told Seeds of Gold that application of human faecal manure can multiply maize output phenomenally. Passing a kilogramme packet of treated human compost, without the faintest trace of smell across this writer’s face, the don described the tests they had done to conclude that the manure could increase soil fertility and crop production in one fell swoop.

The tests comparing maize harvests from human manure, artificial fertiliser and using nothing showed one-hectare plots producing nine, five and two tonnes of maize. The two tonnes realised without fertiliser may be on the upper side given the healthier status of the experimental plots.

Fellow soil scientist Richard Onwonga said that maize production on moderately managed soil ranges between 0.5 (equivalent to 5.5 bags of 90kg) to 2.5 (27 bags) tonnes per hectare.

Crop nutrients

They did a similar study on potatoes—Kenya’s second staple crop after maize. Plots receiving human faecal gave highest yield compared to inorganic fertiliser.

On average, Peepoo (faecal) compost recorded the highest potato yield (9.32 tonnes per hectare when converted in acreage compared to where no nutrients were applied with 5.7 tonnes/ha tuber yield. Prof Karanja notes that this could be lower on poorer soils, since soils of Kabete are considered more fertile than the average soil.

Human excreta has high potential of supplying crop nutrients, which include 5-7 per cent nitrogen; 3-5 per cent phosphorus; and 1-3 per cent potassium.

Reports, the don says, indicate that per capita human faecal production is 41–93 grams (dry matter), which translates to about 8.04 grams nitrogen; 5.36 grams phosphorus and 2.68 potassium per day (for two visits to the toilet). Human waste also contains carbon and micro-nutrients such as zinc, iron, manganese and copper, which are generally in short supply in many soils.

So, why aren’t we harvesting human waste? In an email interview with Agriculture Principal Secretary Sicily Kariuki, she said the ministry recognises the contribution of faecal waste in the manufacture of fertilisers.

“In some parts of the country, faecal waste is used. This has important implications because productivity is increased at a reduced cost since commercial fertilisers are beyond reach of some farmers,” she said.

However, the ministry has no policy on use of faecal waste for soil fertility, the PS said, and blamed Kenyans’ failure to embrace the manure on traditional taboos. “Cultural inhibitions for some consumers prohibit them from eating food that is known to have been produced using faecal waste,” she said.

The bulky nature of the manures, she said, also pose financial and physical challenges in terms of transport. “However, if the waste is processed and packaged into easily handled products, it holds a big potential for soil fertility enrichment,” Mrs Kariuki said. The ministry, she added, will do a needs assessment study to establish how the use of faecal waste fits in with different cultures.

“If they don’t want to use it raw, why don’t we do biogas and then use the sludge to fertilise the soil?” Prof Karanja proposes.

The crusade for harvesting of biodegradable urban waste, which she wants taken back to the farms to regenerate depleted soils, proposes different digesters for domestic and market waste and for human faecal waste—a practice that is widely used in Asia.

“Can’t we commercialise it?” she asks. “China, widely uses human waste. They process to sanitise it and apply it on their farms.” The alternative is to produce energy through bio-digesters and then exploit the sludge as manure in institutions and high density urban settlements.

Human waste, she says, has been the first choice of fertiliser for Chinese, who “just started using (artificial) fertilisers about two decades ago.”

Prof Karanja alluded to the EcoSan toilet technology that separates urine from dry stuff. “You stop (using the toilet) for about six months to allow pathogens to decay, so you end up with compost,” she explains.