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Groundnut shells provide base for organic fertilizer

Senegal's annual production of groundnuts in the shell amounts to 1 million tons. That means that about 200 000 tons of shells are either incinerated in the furnaces of groundnut-oil factories or left to rot in the desert. Groundnut shells are an abundant raw material and a largely unexploited one.

Senegalese peasants have used groundnut powder gathered after shelling as a low-yielding fertilizer for their gardens, but anything more than that seemed impossible. Agronomists, in fact, maintained that the shells would not ferment and thus could not be used more extensively as an organic fertilizer.

But the problem of disposing of groundnut shells remained, and the Senegalese authorities often, especially beginning in the 1970s, tried to solve it. Years of research and experimentation were needed, but in the end there were results. An environment suitable for fermentation was found. It is a tub in which the shells, ground to a powder, are immersed in an aqueous environment where chemical additives are mixed (e.g., urea, potassium sulphate). The process of fermentation is set off by a "base" of bovine fertilizer and bacterial proliferation is extremely quick: in general four or five days, a week at most.

The mechanism was developed in the 1970s in France in the laboratories of IRCHA (National institute for research on applied chemistry) beginning with wheat straw, and was patented in 1971 by CIDR (International centre for research and development), a non-governmental organization. But it was the 1973 rise in the price of petroleum, with its inevitable repercussions on that of chemical fertilizers-already prohibitive for most African peasants - that led to the practical application of the process. Thus the Senegalese authorities sought the help of CIDR, which had dusted off its own patent.

The first pilot experiment was conducted in 1975, at Bambey, on land belonging to the National Centre for Agronomic Research (CNRA), with credits granted by France and the EEC. All the byproducts of Senegalese agriculture were tested: from sugar-cane bagasse to rice straw to groundnut shells. These last gave the best results: under the control of CNRA agronomists, the fertilizer derived from them, tested on tomatoes, brought record yields of 70-72 tons per hectare.
Of course, that was virtually a laboratory experiment. The land on which the test was conducted had been kept fertile for decades by technicians and researchers and certainly did not represent average Senegalese soil conditions. Nevertheless, the results were sufficiently encouraging that it was decided to build a first factory to produce this new type of fertilizer.

It is going up at Tivaouane, a large suburb on the outskirts of Thi and will use raw material supplied by the shelling plant owned by Aloune Palla Mbaye, a local notable, member of the Senegal national federation of veterans and victims of war, who has assumed the role of patron of the initiative. This plant, which employs a dozen persons, handles, from September to May, varying tonnages of groundnuts: 58 000 in the best years. From 2 000 to 10 000 tons of shells are extracted, depending on how the season went. Now at least part of them will be converted into fertilizers.

The setting up of the plant has been entrusted to the French engineer Pierre Garrigues of CIDR and carried out by CORDIA (the Paris based Company for the Organization of Industrial and Agricultural Development), of which Garrigues is president. "It was believed," he said, "that chemical fertilizers had the definite advantage over vegetable fertilizers. But, at the end of the 1970s, the international scientific community recognized that chemical fertilizers could fulfil their function only on lands with a sufficient content of organic matter." That is, of humus, the colloidal matter of the soil which derives from the decomposition of organic residues and which makes a breeding ground for bacteria. The bacteria in turn metabolize the soil's mineral salts, making them thereby assailable by the plants, and expel carbonic gas, which allows the plants themselves to manufacture their cellulose structure. No chemical fertilizer produces the essential carbon. This is a problem particularly in the tropics, where the soil rapidly becomes exhausted under the combined effects of wind and torrential rains.

"The new groundnut-based fertilizer," says Garrigues, "offers another fundamental advantage: it will cost 20 times less than chemical fertilizers and that will largely compensate for the fact of having to use a larger (triple) dose of it per hectare." In Senegal, as elsewhere in Africa, one of the most urgent problems is, in fact, to reduce to the extent possible the use of chemical fertilizers, which are extremely costly for the peasant economy.

A basic element for the best application of the new technique is the size of the fermentation trench. Research shows that the larger it is, the better the results. Consequently, the trench for the Tivaouane plant should have a capacity of 35 m3 (as against the 7 m3 of the experimental trench at Bambey); and, with two trenches, the unit could set off a production of 500-1 000 tons of fertilizers. That would be offered to horticulturists of the area around Niayes, on the seacoast, Senegal's most important region for fruit and vegetable production.

It is a first step. But it looks like this small industrial unit - which the Senegalese Government is watching with particular attention - established in the right place and in the right way, can, if well managed, demonstrate the usefulness of the new technique and be a point of departure for the creation of similar plants, serving the rural communities of many African countries, beginning with those of the Sahel.

Gabriella Lapasini