Widespread land degradation has been threatening the capacity of the Sasumua catchment, located in Nyandarua county of Kenya, to supply a large percentage (20%) of Nairobi’s fresh water. In an attempt to halt land degradation in the catchment, a biophysical assessment was carried out in 2008 to understand land use, vegetation cover, soil erosion issues and usage of soil and water conservation structures to inform project activities.
I am Evans Kyei, a student of Bangor University in the UK and TU Dresden in Germany (in the joint SUTROFOR program). This summer, I carried out research in the catchment to follow up on the work carried out in 2008. He was on attachment with the World Agroforestry Centre (ICRAF) and the Upper Tana Nairobi Water Fund project.
During my study in 2017, field measurements and observations of land use, vegetation cover, soil erosion and soil and water conservation (SWC) structure prevalence were taken as before using the Land Degradation Surveillance Framework. Interviews were conducted to collect data that was then compared with baseline data. The reason for this was to assess the current status of the land in terms of its soil fertility, soil erosion and vegetation cover and how it has changed over the nine-year period, to inform further project activities.
Results show that over a nine-year period there has been a lot of land use change, with the conversion of about 49 sampled plots from grassland to cropland, and this has partly been driven by a decline in grassland productivity. Although tree density (the number of trees in a given area) has remained low and has not changed significantly (with an average 101 trees per hectare recorded in 2008 and 133 trees per hectare recorded in 2017), shrubs (which may represent future trees) have decreased significantly (from 207 shrubs per hectare recorded in 2008 to 16 shrubs per hectare recorded in 2017). Herbaceous cover has increased on all plots and was highest on grassland plots, however, the quality of grass was perceived as poor and caused lack of feed for livestock.
The number of plots with soil erosion had decreased across the catchment due to the number of plots with soil and water conservation structures. These structures were mainly on cropland plots and were found to be effective in controlling soil erosion. Although soil erosion had been reduced, during interviews farmers said there had been a continued decline in soil fertility. This indicates that the soil and water conservation structures alone are not enough for enhancing soil fertility in the catchment, and may need to be complemented with other soil fertility improvement measures. Overall, farmers’ perceptions of soil erosion trends and the effectiveness of soil and water conservation structures agreed with the findings from field measurements and observations.
Some land degradation problems expressed by farmers in the catchment include soil fertility decline (left), grass productivity decline (middle), and deforestation (right).
The study recommends the following:
1. Promotion of agroforestry practices (which is lowly practiced currently) across the catchment as it has the potential to increase tree and shrub cover, as well as address land degradation problems such as soil fertility decline. However, trees that have the ability to withstand “poor drainage soils” (characteristic of the lower catchment), fix nutrients and provide less competition with crops should be prioritized, in order to increase farmers adoption of such practices
2. In order to further reduce soil erosion, projects should take advantage of the fact that farmers perceive local soil and water conservation structures to be very effective and support them to increase their adoption, especially on grassland plots which are the land use most prone to soil erosion but also where farmers do not invest in soil and water conservation structures
3. Future research should focus on laboratory assessment of soil fertility in the catchment in order to advice farmers appropriately about how to improve their soil fertility decline, a land degradation problem that was highly expressed by farmers as affecting them. If possible, other measures that enhance soil fertility should be implemented together with the local soil and water conservation structures, as they alone are not enough in enhancing soil fertility in the catchment (although they are effective in controlling soil erosion).
The three months I spent in the field conducting this study gave me the opportunity to learn great new skills in biological and socioeconomic data collection and analyses. It also allowed me to meet great new career mentors, and experience the awesome Kenyan culture through several interactions with the nice people of Kenya. For instance, I learned to speak some Swahili and also to eat some local Kenyan food, and all these contributed to the success of this study and my wonderful time in Kenya. With all the new skills I learned and the experiences I had, I feel more empowered to carry out other future research. I am forever grateful to my project partners (i.e ICRAF) and my supervisors for this great opportunity. My sincerest gratitude also goes to the local farmers and facilitators in Sasumua catchment for sharing their invaluable knowledge and providing enormous support during this study
By Evans Kyei