Soil fertility degradation is a major constraint to food security – Expert

Cassava - a staple food in Ghana

Soil fertility degradation triggered by nutrient removal through plant uptake; erosion and leaching, described as soil mining, coupled with low application of fertilizer is the most important constraint to food security in Sub-Sahara Africa.

“In this Region, it has been reported that soil mining may contribute from one-third to as much as 80 per cent of farm output in some locations,” Professor Seth K.A. Danso of the Department of Soil Science; College of Agriculture and Consumer Science, University of Ghana, said on Monday.

He was delivering “The 43rd J.B. Danquah Memorial Lectures,” one of the major activities of the Ghana Academy of Arts and Sciences (GAAS), on the theme:“The Earth That Nourishes Us: Soils and Humanity.”

Prof. Danso said “among the technologies introduced into modern agriculture is the availability and use of chemical fertilizers to correct nutrient deficiencies in the soil, or to replace nutrients lost from soil through plant uptake, erosion and leaching. However, nowhere in the world is fertilizer use as low as in Africa”.

He said data on nutrient balance over the past 30 years indicated that annual net losses of nitrogen, phosphorus and potassium  have been in the order 22, 2.5 and 1.5 kg/ha, in that order.

“What is most disturbing is, that soil degradation once it starts and is not corrected, results in further declines in soil fertility and reduced yields of subsequent crops. The population thus seems to be trapped in a vicious poverty cycle involving soil degradation, and lack of resources or knowledge to generate adequate income and opportunities to overcome the degradation, resulting in further land degradation,” he said.

“The gradual degradation of soil caused by soil fertility decline and the continued exploitation of the fragile resource base depleted of many plant nutrients is a menace to rural African communities, in terms of food security”, Prof Danso said, adding “There is, therefore, a critical need to develop and implement  management options that mitigate soil fertility degradation.”

“Soil nutrient balances measured for many cropping systems in several countries in Africa have been negative, indicating that farmers are mining the soil. It is, therefore, essential for farmers and other stakeholders, keen to promote sustainable agricultural production to monitor soil quality and take measures to avoid or minimize soil degradation to preserve the production capabilities of the land and protect the wider environment, Prof Danso said.

He said soils contain biota, whose activities affect the chemical, physical and biological status of the soil- the decomposition of soil organic matter by microbes including bacteria, fungi and actinomycetes release locked up nutrients for plant uptake, while Rhizobium converts atmospheric nitrogen for the use of legumes and thus making it possible for them to grow on nitrogen-deficient soils.

Prof Danso said “currently little is known about how agricultural activities change a soil’s biological properties and the potential cost to the food and fibre system of damage to soil biodiversity, adding that this knowledge gap could be overcome through the development of soil biodiversity indicators.

He said the soil biodiversity issue is also closely related to soil organic matter – “soil with adequate amounts of organic matter have good aggregation and tilth, permit water and air infiltration, are resistant to erosion, and help to provide favourable biological habitats.

Turning to climate change, Prof. Danso said “much effort and expense are currently being directed at reducing anthropogenic conditions to the greenhouse effect and its potential for altering the earth’s climate but explained that gasses produced by biological processes, such as those occurring in the soil, account for approximately half of the problem.

“Of the five primary greenhouse gasses, only CFCs (chlorofluorocarbons) are exclusively of industrial origin, while much of the increase in atmospheric carbon dioxide levels comes from a net loss of organic matter from the soil system.

“When soils are poorly aerated, as in the case in rice paddies and wetlands, methane rather than carbon dioxide is produced by organisms in decomposing soil organic matter. For example about 70 per cent to 80 per cent of the methane released from flooded soils escape to the atmosphere through the stems of rice plants or natural marsh grasses.”

He said “thus flooded rice soil which supplies food for over two billion people, also accounts for up to one-fifth of the global emission of methane, thus becoming the Akan proverbial “Santrofi Anoma”.

Prof Danso said soils could be managed to play a major role in controlling the emission of greenhouse gasses.

GAAS was established by an Act of Parliament on the initiative of Osagyefo Dr Kwame Nkrumah, Ghana’s First President, and was inaugurated on 27 November 1959. The mission of GAAS is to encourage the creation, acquisition, dissemination and utilization of knowledge for national development through promoting learning.

Its stated objectives over the years have expanded to contribute actively to the development of Ghana and Africa in general, by examining and addressing crucial issues of development. Its values include promotion of professionalism and commitment; excellence; integrity and relevance.

It is a national repository of high-level multidisciplinary knowledge; national access to the highest intellect and experts in diverse academic fields and credibility of the Academy and its fellows. It has the ability to produce high quality publications and the capacity to undertake targeted research.

Source: GNA

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