Aida – tell us what you are up to?

I am currently doing fieldwork within the framework of our Formas and VR - funded projects and in collaboration with the World Agroforestry Centre (ICRAF).

ICRAF has developed a systematic landscape-level assessment of soil and ecosystem health called the Land Degradation Surveillance Framework (LDSF). This methodology provides a biophysical baseline and a monitoring and evaluation framework for tracking processes of land degradation and recovery over time. There are over 200 sites across the global tropics where the LDSF has been employed, and the network of LDSF sites keeps growing. ICRAF is currently undertaking an LDSF sampling campaign across five sites in Kenya.

Among the soil health indicators measured as part of the LDSF, infiltration capacity is of great interest to our project. I have joined ICRAF’s sampling campaign in Kenya to conduct additional dye tracing experiments to complement the data on infiltration capacity.

Following each infiltration experiment, we add a solution of Brilliant Blue dye, a common food colorant, and let it infiltrate into the soil. The next day, we dig a soil pit and take a picture of the stained soil profile, which provides visual evidence of the water flow pathways in the soil. These images can then be used to estimate the degree of preferential flow, which tells us to what extent infiltrating water moves along certain preferred pathways such as root or termite channels.

One of the sampled plots in Thange(Makueni county, Kenya), where maize is grown under scattered baobab trees

Why is this research important?

Water reaching the soil surface can either infiltrate into the soil or remain on the surface, generating surface run-off. Once it has infiltrated into the soil, water can flow slowly through the soil matrix or move faster throughout preferred pathways. Therefore, soil infiltration capacity and the degree of preferential flow are two fundamental soil properties influencing soil erosion, flood risk, soil and groundwater recharge, and dry season flows.

All these, in turn, have a critical role in shaping people’s livelihoods. In tropical drylands, rainfall intensities are typically high and soils prone to degradation. This hampers the recharge of soil water, also known as green water. Green water sustains rain-fed crops and all other non-agricultural vegetation, and it is essential in areas such as Sub-Saharan Africa, where it is estimated that food production depends on green water resources by more than 95%.

Groundwater recharge is also key in water-limited environments. If managed sustainably, groundwater provides a reliable source of fresh water for human consumption, irrigation or industries that can serve as a buffer in times of surface water scarcity. Moreover, groundwater stores sustain dry season flows in streams, which are also vital in drylands.

Data collected during this fieldwork campaign will allow us to explore factors that influence infiltration and preferential flow across landscapes. This knowledge will be of great importance to help designing better land management practices and policies to improve water resources and reverse and prevent land degradation in tropical drylands.

Related articles:

Native trees in African drylands serve as water harvesters (ICRAF)

Can more trees improve groundwater levels? (SIANI)

Lessons from Kenya on how to restore degraded land (The Conversation)

Photos: Aida Bargues Tobella (private)

Contact: Aida.Bargues.Tobella@slu.se for more information.