Suchergebnisse

Agriculture provides the most essential service to mankind, as production of crops in sufficient amounts is necessary for food security and livelihood. This chapter examines the question of whether organic agriculture can produce enough food to meet future demand. This question relates to a moral imperative and any evaluation must therefore be based on objective scientific facts excluding ideological bias, political correctness, economic incentives or environmental opinions. The chapter begins by defining the conditions necessary for a stringent evaluation of crop yields and explains potential pitfalls. Yield data from national statistics, organic and conventional long-term experiments and comparative studies are then compiled and evaluated, followed by a discussion of the main factors behind low-yielding production. In a global perspective, the scientific literature shows that organic yields are between 25 and 50% lower than conventional yields, depending on whether the organic system has access to animal manure. The amount of manure available on organic farms is usually not sufficient to produce similar crop yields as in conventional systems and therefore green manures are commonly used. However, organic crop yields reported for rotations with green manure require correction for years without crop export from the field, which reduces average yield over the crop rotation. When organic yields are similar to those in conventional production, nutrient input through manure is usually higher than nutrient addition in conventional agriculture, but such high inputs are usually only possible through transfer of large amounts of manure from conventional to organic production. The main factors limiting organic yields are lower nutrient availability, poorer weed control and limited possibilities to improve the nutrient status of infertile soils. It is thus very likely that the rules that actually define organic agriculture, i.e. exclusive use of manures and untreated minerals, greatly limit the potential to increase yields. Our analysis of some yield-related statements repeatedly used by advocates of organic agriculture reached the following conclusions: Organic manure is a severely limited resource, unavailable in quantities sufficient for sustaining high crop yields; legumes are not a free and environmentally sound N source that can replace inorganic fertilisers throughout; and low native soil fertility cannot be overcome with local inputs and untreated minerals alone. Agricultural methods severely limiting crop yields are counter-productive. Lower organic yields require compensation through expansion of cropland – the alternative is famine. Combining expected population growth and projected land demand reveals that low-yielding agriculture is an unrealistic option for production of sufficient crops in the future. In addition, accelerated conversion of natural ecosystems into cropland would cause significant loss of natural habitats. Further improvement of conventional agriculture based on innovations, enhanced efficiency and improved agronomic practices seems to be the only way to produce sufficient food supply for a growing world population while minimising the negative environmental impact.