Long-term performance of organic crop rotations in the tropics: First results from a high and a medium potential site in sub-humid Central Kenya

Organic Agriculture is perceived by many stakeholders as a promising approach to increase food security in developing countries. However, only few attempts have been made so far to assess agronomic and economic performance of Organic Agriculture in these regions in a systematic way. The Research Institute of Organic Agriculture (FiBL), together with its partners, is presently establishing long-term comparisons of farming systems in various agro-ecological and socio-economic contexts to study the different parameters that are essential for sustainable development. To date, three study areas have been selected: (a) a sub-humid area in Kenya where farming is subsistence-oriented; (b) a semi-arid area in India where cotton is produced for the export market; and (c) a humid area in Bolivia where cacao and other perennial products are produced for the export and domestic markets. The key elements are replicated long-term field trials. These are complemented by farm surveys and short-term trials under on-farm conditions. This network of comparison of farming systems in the tropics is expected to (1) put the discussion on the benefits and drawbacks of Organic Agriculture on a rational basis; (2) help to identify challenges for Organic Agriculture that can then be addressed systematically; (3) provide physical reference points for stakeholders in agricultural research and development and thus support agricultural policy dialogue at different levels. In Kenya, the two trials sites are located in a high potential zone in Meru South District (Chuka) and in a medium potential zone in Maragua District (Thika). They consist of four treatments: conventional and organic, each at a low and a high input level, representing subsistence oriented and commercial farming, respectively. Maize, brassicas and maize were planted during the first, second and third season respectively in both organic and conventional plots. In the first three seasons, we found the following results: in Chuka, organic yields of the low input treatments were on average 4% lower than conventional yields. On the high input level, organic yields were 6% lower. In Thika, organic yields were on average 57% (low input level) and 33% (high input level) lower than conventional yields. It is assumed that the organic crops in Chuka could benefit from N and P mobilisation from the soil. In Thika, where N and P were probably less available, the crop depended on the easily soluble nutrients applied in the conventional treatments. The effect of lower nutrient availability in the organic treatments in Thika was possibly aggravated by serious drought spells during the second and third season. The questions of interest are a) whether the organic treatments can keep the yield level of the conventional treatments in Chuka or if they will go through a depression typical for conversion from conventional to Organic Agriculture; and b) if the organic treatments can improve soil fertility and thus the organic yield levels in Thika in the coming years.