关键词: organic farming , conventional farming , tropics , subtropics , carbon sequestration , yield , soil quality , soil organic carbon

Abstract: Organic farming aims to stimulate soil fertility by avoiding the use of synthetic fertiliser inputs, relying instead on locally available natural resources. It is regarded by many as a sustainable alternative to conventional farming because it ensures higher biodiversity, restricts environmental pollution, prevents land degradation and is easy to apply for smallholder and subsistence farmers. Although widely practiced and studied in temperate regions, little is known about the potential overall benefits of organic farming in the tropics and subtropics. This paper addresses this gap by undertaking an analysis of the differences between organic and conventional agriculture in the tropics and sub-tropics based on an extensive literature review including 88 papers with 458 data pairs. The comparison is based on three main indicators: yield, gross margin and soil organic carbon (SOC). The differences between the organic and conventional systems for each of these main indicators is represented by the ratio of the value of the indicator in the organic system divided by the corresponding value in the conventional system. This was initially calculated for each data pair individually, and grouped by a variety of explanatory factors, such as precipitation, human development level, soil texture, crop type, organic input type, time after conversion and certification. The results demonstrate that under organic management, yields were on average 26% higher, gross margins 51% higher and soil organic carbon 53% higher than under conventional management. The highest yield increases in organic cropping systems were achieved in the least developed countries, in arid regions and on coarse soils. For gross margins, certification was the main reason for differences between organic and conventional systems. Certified farmers, mostly located in developed countries, receive significantly higher prices. Furthermore, organic farming in the driest regions results in higher profits than in other regions. Even though soil organic carbon was significantly higher overall under organic management, the results do not show significant differences when grouped by the explanatory factors. They do however suggest that the highest carbon sequestration potential occurs in systems that had a high level of inputs, in regions with 1 000-1 500 mm of rainfall and on clayey soils.

Key words: organic farming , conventional farming , tropics , subtropics , carbon sequestration , yield , soil quality , soil organic carbon