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[KAMPALA] The weight of a banana crop can soar by up to 100 per cent when moderate amounts of specific inorganic fertilisers are applied, scientists in Uganda have shown.

Some 70 million people across Africa rely on bananas for food or income, but less than five per cent of banana farmers use any fertiliser, according to Piet van Asten, a system agronomist at the International Institute of Tropical Agriculture (IITA), in Uganda, who conducted the study with Lydia Wairegi, a PhD student at Uganda's Makerere University.

They set up experiments with 200 banana fields in central and southwestern Uganda.

Analysing banana leaves allowed them to assess nutrient deficiencies and then apply specific fertiliser that would supply only those nutrients.

Even a modest application of a fertiliser doubled the yields from 10 to 20 tonnes per hectare per year in some areas in the study.

Adding a fertiliser also shortened the crop cycle, yielding more frequent harvests. And according to a related study by IITA and Uganda's National Agricultural Research Organisation, it also improved the taste.

"Before the IITA study, no large-scale evaluation of nitrogen, potassium and phosphorus fertiliser recommendations in farmers' fields across Uganda had been done," said Asten.

He quoted several reasons why farmers have not been using fertilisers on banana crops: high cost, scarcity, the fact that they are not available in small packages, lack of knowledge, and the belief that fertilisers damage soil quality and banana taste.

Asten admits that blanket fertiliser application can be a waste of money. Farmers need to match local nutrient deficiencies with a specific fertiliser that adds those exact nutrients to improve their yield.

IITA and its partners have now developed site-specific recommendations for fertiliser application.

But Jane Nalunga, senior training officer with National Organic Agricultural Movement of Uganda insisted that farmers should pay attention to sustainability and long-term effects on the soil. What is useful for banana yields in the short run, might be detrimental to the soil quality in the long run, she said.

She added that "The majority of [smallholder] farmers cannot afford chemical fertilisers at 120,000 Uganda Shillings [US$58] for a 50kg bag of nitrogen-phosphorous-potassium to be applied to 100 stools [stems] of banana".