Soil fertility and the benefits of earthworms and termites

28 juni 2010

Soil macrofauna, especially earthworms and termites, are important components of the soil ecosystem. A better understanding of the management of soil macrofauna can lead to improvement of infertile or degrading soils in sub-Sahara Africa. Many farmers, however, perceive macrofauna as pests. They often used control measures against termites, without being aware of the beneficial effects of termites. This knowledge is important in designing agricultural management systems aimed at increasing long-term soil fertility in sub-Saharan Africa.

WOTRO researcher Fredrick Ouma Ayuke received his PhD for his research into crop management at Wageningen University on 11 June, 2010.

Soil macrofauna
Earthworms and termites are an essential component of our ecosystems and are important ecosystem engineers. These soil macrofauna influence the formation and maintenance of soil structure and regulate soil processes, such as organic matter decomposition (rotting) and nutrient dynamics. Under continuous cultivation, tropical soils are very susceptible to rapid losses of soil organic matter and degradation of soil structure. Therefore, an understanding of the effects of soil macrofauna and management practices, and their interrelationship, is very important to improve soil quality and enhance crop production.

Agricultural management practices
Fredrick researched 12 long-term trial fields across the sub-humid to semi-arid tropical zones in Eastern and Western Africa. He showed that continuous crop production has significant negative effects on earthworm diversity, but little effect on termite diversity, as compared to long-term fallow. Agricultural management resulting in high soil-carbon increases earthworm and termite diversity as compared to low-carbon soil. Long-term application of manure in combination with fertilizer results in higher earthworm diversity and biomass. This is associated with improved soil aggregation and enhanced carbon and N (nitrogen mineralized from soil organic matter) stabilization within this more stable soil structure. These practices therefore result in the dual benefits of improving soil physical and chemical properties.

A micro morphological study of undisturbed soil thin sections showed that fallowing, conservation tillage plus residue application (in East Africa) and hand-hoeing plus manure (in West Africa) enhanced biogenic soil structure formation. This results in a well developed soil structure and a continuous pore system characterized by many faunal channels. In contrast, intensive tillage and absence of organic inputs resulted in soil with less biogenic soil structural features.

Farmers
Frederick also showed that farmers are aware of termite activities, nesting habits, and also know local names of different types of termites. This indicates that they are interested in this macrofauna group. However, 90% percent of the farmers perceive termites as pests to crops. Farmers’ negative perception about termites needs to be looked into if beneficial functions of termites will be exploited and integrated into soil fertility management recommendations. This calls for more research to assess the trade-offs between positive and negative impacts of termites on crop yields, as well as to get an understanding of the effects of different termite control strategies used by farmers on agro ecosystem functions.

Local circumstances
The knowledge gathered from this study constitutes the baseline information that is important in designing agricultural management systems aimed at increasing long-term soil fertility in sub-Saharan Africa. Although fallowing is an attractive alternative practice in the conservation biodiversity for enhanced ecosystem functioning, it may not be practical in many parts of sub-Saharan Africa. Land is limiting and fallowing has to be shortened due to increased population size. Given the varied agroecological conditions which differently affect faunal activities, recommendation of these practices should be tailored to meet the circumstances of target farmers.

Dissertation: Soil macrofauna functional groups and their effects on soil structure, as related to agricultural management practices across agroecological zones of Sub-Saharan Africa
Promotor: Prof. Dr. L. Brussaard
Co-promotors: Dr. M.M. Pulleman, Dr. B. Vanlauwe, Prof. Dr. J. Six

Source: Wageningen UR Digital Library