14 April 2015

For a more sustainable agriculture : three myths to debunk

2015 is the International Year of Soils. This is the right time to debunk some of the prevailing myths that prevent us from managing properly our soils.

Traditionally and over many centuries since the invention of agriculture, humankind had been managing soils by leaving land in fallow for a period of time sufficient for them to reconstitute their fertility. In a few areas of the world such extensive farming systems still exist but, in most of the world, population pressure has made it that fallow has been progressively reduced and finally abandoned. To compensate for the loss of soil fertility that resulted from the change of the way land is being managed, the industry proposed the wide use of chemical fertiliser and ploughing by increasingly powerful and expensive equipment [read more]. But there is ample evidence now that this option is not a sustainable solution and soil fertility has become one of the most important limiting factor for world agriculture.

In his article ‘‘Restoring our soils by learning from history’’, R. Bunch identifies three myths that prevail in our way of considering soils for agriculture and that need to be debunked:

Myth 1: productive soils inevitably deteriorate over time. A large number of experiments have shown that soil fertility has been decreasing despite using chemical fertiliser and that this ‘‘loss of fertility [is] correlated with decreasing soil organic matter levels and the resulting availability of nutrients’’. However, evidence shows that ‘‘humid tropical forests the world over, by maintaining the soil organic matter content, have maintained impressively high levels of biomass productivity for millions of years, with no fertilizers and often on very infertile soils’’. Although we may have some doubts about the relevance of the example of tropical forests given by Bunch (they are not harvested and therefore live in a relatively closed circle), it is known that there are possibilities, through better crop management (use of animal or green manure and compost, intercropping with legumes and trees) to maintain a high level of organic matter content in the soil which slowly releases the nutrients required by crops and fixes water, thus increasing resistance to drought.

Myth 2: soils need to be ploughed to stay friable and productive. Once more, evidence shows that ‘‘tropical forest soils […] never ploughed […] after millions of years […] are far more friable and naturally productive than most agricultural soils’’. In this case, the experience with conservation agriculture and zero or minimum tillage (mentioned by Bunch) shows that absence of ploughing is actually better for soil structure.

Myth 3: good modern farmers must use monocropping. There is ample evidence that there are advantages in crop associations both in terms of soil fertility (association of Nitrogen fixing legumes and cereals or agroforestry) and of crop protection (push-pull). There is also evidence of the negative consequences of monocropping in terms of animal biodiversity (e.g. bees) and vulnerability of crops to pests and diseases.

These myths need to debunked and implications drawn on how agriculture can be better managed to preserve the soil and its contribution to sustainable agricultural production. R. Bunch mentions a few practical solutions in his article (legumes as green manure/ cover crops, using trees for dispersed shading).

These points need to be kept in mind to develop and adopt more sustainable agricultural practices [read more]

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Reference:

Bunch, R., ‘Restoring our soils by learning from history, AgriCultures Network, 2015

Last update:    April 2015

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