Soil Fertility and Erosion
Over the past hundred years, the sophistication of localised adaptive soil conservation and land use has suffered, because these skills have increasingly been replaced by the generalised use of synthetic mineral fertilisers. These fertilisers are easily applied, are seemingly inexhaustible and have replaced the long-term conservation and building-up of soil fertility. Each year, more than a 100 million tonnes of synthetic nitrogen fertiliser are manufactured using the eponymous Haber-Bosch industrial process for making ammonia, developed by German chemists Fritz Haber and Carl Bosch. Since the process only works at high temperatures and pressure it requires large energy inputs, making agriculture in general and soil fertility in particular dependent on the oil price.
The boost in nutrients, provided by nitrogen fertilisers, made possible the steep increase in agricultural production over the past century and enabled the current overproduction. However, it has the same fatal effect on soils as a drug: the natural soil fertility and especially the humus formation are both affected. Soils are depleting and leaching faster; soil acidification is accelerating; or the soils need higher doses of mineral fertilisers. At the same time, mineral fertilisers tempt farmers to abandon the more time-consuming, knowledge-based and labour-intensive methods of conserving soil fertility. Or they are compelled to do so for economic reasons. Without the introduction of industrially produced mineral fertilisers, farmers would not have been able to specialise in just a few crops, have monocultures or give up animal husbandry."Modern best practice guidelines for conventional production systems advise the full use of all indigenous fertility sources (composts, crop residues, and animal manures), with mineral fertilizers employed to bridge deficits between crop needs and indigenous supplies.“ (Global, p. 183)
The IAASTD makes the case for an intensive relearning of this knowledge for both industrial and small-scale agriculture, as well as its re-application in agricultural research. The report calls for refraining from all forms of agriculture and soil management that disregard the fundamental value of fertile soils. This includes over-fertilisation, the overexploitation of sensitive soils, and exposure to water and wind erosion, which can be prevented for example with a stock of trees or hedges. Other harmful practices include the use of heavy machinery which can lead to soil compaction, as can deep or unnecessary tillage with a plough. But soils are also threatened by the sealing of fertile land close to cities in industrial regions.
