GM crops - part of the solution for soils?

It's well known that sub-Saharan Africa has some of the oldest and poorest soils in the world. Thousands of years of weathering have leached the nutrients, leaving the soil highly acidic, (on average between pH 3.5 and 4.5), which causes aluminium and manganese to become soluble and thereby toxic to plants. The deeply weathered African soils also suffer from high levels of iron and aluminium oxides, which also hinder plant growth by chemically 'locking up' phosphates. Combined with chronic shortage of water, the results of such poor soil fertility for African farmers is easy to predict. A study on vegetable production in South Africa showed that soil acidity and drought stress accounted for over 80% of yield losses. Diseases and pests accounted for the remaining 20%. A similar picture emerged from a study of community vegetable gardens; water stress, soil acidity and low phosphate and potassium levels were the dominant factors in reducing yields.

There is unlikely to ever be a single 'magic bullet' that can solve the problem of poor soils in Africa, but there are signs that genetically modified crops could be one element in a broader solution. The logic behind this is simple; incorporating crop residues into the soil is an obvious and low cost way of rebuilding soil health. Not only do the residues contain valuable nutrients, they also moderate extremes of acidity. But the vicious circle of low productivity means that just as crop yields are low, so are the quantities of crop residue; there's generally very little for the farmers to put back into their soils once their crop is harvested. Genetic modification is potentially a way of breaking this chain, since crops engineered to prosper in the face of drought, disease and pests, are, as something of a side effect, also going to offer greater biomass post harvest.

Evidence of the potential of GM crops in sub-Saharan Africa is already coming out of research being done by the University of Cape Town. For example in the case of drought tolerance, a research group in Cape Town is currently working to transfer genes from an indigenous 'resurrection plant' into food crops. Resurrection plants are capable of drying up almost completely, yet resurrecting to full health when rain finally arrives. If the right genes could be transferred to food crops, losses to drought might be significantly reduced and more organic matter could be returned to the soil. Interestingly, many proteins that confer tolerance to drought also confer tolerance to other stresses such as high and low temperature and salinity. The genes of the resurrection plant could offer multiple benefits.

The same case can be made for GM crops that can stand up to pests and diseases. Attack by insects slows down plant growth, and robs the farmer of potential organic material. Traditional plant breeding to counter insect attack has only had limited success, and many farmers cannot afford pesticides. Insect resistance is a genetic trait that is already being widely exploited in the USA, and GM insect resistant cotton has been successfully introduced in South Africa. Consequently, commercial farmers are now using less insecticides, and the environmental benefits are clear, as non-target insect species are returning to the cotton growing areas, as are insectivorous birds, and, most encouragingly, a number of species of frogs. (Frogs, due to their porous skin, are supremely sensitive to foreign chemicals, and for them to be returning shows the extent of the environmental clean-up). This improvement above ground is likely to benefit the soil; although the relationship between life above and below ground level is little understood - soil scientists only claim to understand the workings of around 2% of the micro-organisms that live in the soil - it is reasonable to assume that environmental health in one area will improve the health of the whole system.

Virus resistance is another area of research, that could offer hope for farmers and their soils. Africa is home to a number of unique plant viruses, such as maize streak virus and African cassava mosaic virus. Recently cassava mosaic virus wiped out the entire cassava crop in Zambia. As plants have no immune system the only way to combat these diseases has been by traditional plant breeding or by trying to kill the viral insect carriers by spraying. Unfortunately poor farmers cannot afford insecticides and breeding has been only partially successful. However, scientists in Africa, together with partners elsewhere, are developing GM maize and cassava with "built in" resistance to these viruses.

Thus, genetic modification offers not only the prospect of greater productivity directly through increased yields, but also the prospect of larger quantities of crop residues, which can build soil fertility to the benefit of subsequent crops.

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