Effects of termites on soil fertility

Effects of the levelling of Macrotermes falciger termite mound and the spreading of their materials on the spatio-temporal variability of Ferralsol fertility in Lubumbashi

Termites are one of the dominant groups of soil macrofauna in the tropics. They play a central role in the functioning of these ecosystems by regulating the distribution of natural resources such as water and nutrients. Through their trophic, construction and drilling activities, these tropical ecosystem engineers greatly influence the biological, chemical, mineralogical and physical properties of tropical soils. Compared to the ferralitic soils (surrounding termites mounds), Macrotermes falciger are frequently enriched in CaCO3, Corg, basic cations (Ca2+, Mg2+, and K+), negative charge (CEC), fine particles, clay minerals of types 2: 1 and oxides of Mn and Fe weakly crystallized. As a result, studying the impact of termites on soil properties and functioning, is of crucial importance for sustainable agriculture and food production, with a population explosion that doubled between 2000 and 2017, and an additional demographic surge in population. millions of people is projected for 2050.

Photo: Kristof Van Oost 

The large-scale commercial agriculture that has recently been introduced to the region profoundly affects the functioning of these soils. Increasingly, termite mounds are leveled and considerable volumes of termite mound materials are being spread and mixed with the plowed horizons of commercial farms. Given the particular properties of termite mounds (alkaline pH, nutrient enrichment) the physical mixing of these materials with the soils of the plowed horizons induces a great spatial heterogeneity of the properties of the soil on a small scale. However, so far there is very little information showing how these practices modify the chemical and physical properties at the field scale. However, it is a major challenge because the variation in soil fertility induced by these practices has a great impact on the production of plant biomass. In addition, the observations show a temporal difference because plowing spreads and mixes the materials of termite mounds which become more and more exposed to pedogenetic processes (dissolution-precipitation, fragmentation, erosion, leaching, etc.).

Photo: Kristof Van Oost 

To meet the challenges raised above there is a need to characterize the ground system in time at a fine spatial resolution. Nevertheless, traditional methods for measuring soil properties on such a scale are not possible because of their cost. However, recent advances in diffuse reflectance spectroscopy in the visible and near infra-red (NIRS) allow to estimate the key parameters of soil related to fertility including: organic matter, texture, nitrogen, CEC etc. . Recent work initiated by the host institution (UCL) has shown that UAV-based spectral sensors can now provide ground information at unprecedented spatial resolution. This technique is particularly relevant to this research proposal, as it responds to the high spatial variability of soil within the field relative to termite activity.
The objective of this doctoral research is to improve our understanding of the effects of termite mound grading and the spreading of their materials on the spatial and temporal evolution of soil chemical and physical fertility and on agricultural productivity by analyzing the physico-chemical soil fertility, spatial and temporal variability in a grading context and analyzing how this spatio-temporal variability affects agricultural production.