KATJA KEHLENBECK, BRIGITTE L. MAASS
Georg-August-Universität Göttingen, Institute for Crop and Animal Production in the Tropics, Germany
The maintenance of soil fertility is one of the prerequisites of sustainable agricultural systems. Tropical homegardens are generally regarded a sustainable agricultural production system, particularly due to the sustainable soil fertility management by the gardeners. They are said to apply mostly endogenous fertilisers to maintain soil fertility. The multilayered vegetation structure of homegardens is often stated to protect the soil from erosion. However, there is little quantitative data to support these statements. This study aimed to assess soil fertility in homegardens as well as the influence of certain management practices on it over a time period of two years (in 2001 and 2003).
In 30 homegardens randomly selected from three villages adjacent to the Lore Lindu National Park in Central Sulawesi, soil samples were taken in different management zones. Besides pH-value, also bulk density, total C and N as well as plant available P and K were analysed. For assessment of soil erosion, soil samples were taken for analysis of Caesium 137 in three selected homegardens. Information about soil fertility management was gathered in individual in-depth interviews with gardeners, including questions on fertiliser use, frequencies of fertiliser application, methods and frequency of soil preparation, among others.
Results showed that soil fertility in homegardens was dynamic. Both increase and decrease of different characteristics were found. Particular management practices, such as fertilising with ash, were observed to increase pH as well as available P. Although existing, some of the endogenous fertiliser resources were not usually applied (e.g. pig manure) due to lack of knowledge of the gardeners. Specific management zones of the gardens, such as the vegetable area, suffered more from erosion than others, for example, the cacao or fruit tree area, where thick litter or herbage layers were typical. In addition, soil of the vegetable area often showed a higher bulk density, but a lower content of C, N and available P than soil of the other management zones.
In conclusion, soil fertility management in homegardens is patchy and not sustainable per se. Special management practices may need to be improved.
Keywords: Central Sulawesi, homegardens, soil fertility management