Soil, Seeds and Science

In Kenya (and globally), grasslands are highly important for food production, biodiversity and as carbon stores. But grasslands, particularly Kenyan savannas (grasslands with scattered trees and shrubs, found in dry regions) are under threat from overgrazing and climate change.

Of particular concern is the damage this is doing to the soils under grasslands, as this can have long term effects on grass growth, biodiversity and carbon storage.

That's why scientists from ILRI (the International Livestock Research Institute), Lancaster University in the UK, and the Technical University of Munich are investigating ways to revive degraded soils and the grasslands they support.

Read on to find out more about what is being done to restore soil and grassland in Kenya...

Grasslands are highly important for food security, human nutrition and rural economies, with livestock grazing supporting the livelihoods of over at least 600 million people globally and accounting for 90% of rural employment in Kenya (ilri.org).

They are also valuable ecosystems in their own right, supporting diverse communities of plants, insects, birds and mammals.

Grasslands can sequester (capture) and store a considerable amount of carbon in both the soil and vegetation. Depending on their condition and how they are managed, grasslands can either be sources or sinks for carbon, and globally, this has huge implications for climate change.

Conversion of grasslands to arable land can cause huge losses of biodiversity and carbon, degradation of soil, and flooding due to lower levels of infiltration and greater runoff.

It is therefore vital that we protect grasslands and the soils beneath them.

Grasslands across the world are under threat from human activities such as land use change, overgrazing, invasive species and climate change (increasing frequency of droughts and/or flooding).

• Drought and flooding: While savanna plants and soils are adapted to be resilient to drought, they may not be able to survive extreme weather patterns.

• While grazing is an important service provided by grasslands and can support healthy ecosystems, overgrazing causes soil to become compacted, reducing soil water storage and damaging soil structure. Grazing heavily removes too much vegetation, leaving the soil bare and vulnerable to erosion by wind or water. Bare soil also opens up opportunities for...

• ...Invasive species, which may not be palatable to livestock, and may outcompete more desirable plants, reducing grazing capacity of the land.

Impacts of overgrazing or drought on vegetation is often very visible, but what is less obvious is how these threats affect the soil beneath.....

Soil is a whole living world beneath our feet. Made up of minerals (like sand and clay), organic matter (decomposed plants and animals), air and water, soil is home to a huge diversity of life, from tiny microbes and fungi to more visible earthworms and insects.

Soils are key to plant growth, providing water and nutrients to plants and anchoring plant roots.

Beneath our feet there is constant activity as soil organisms decompose plant matter, convert nutrients to forms usable by plants, fix nitrogen from the atmosphere and sequester carbon secreted by plant roots.

Healthy soils are therefore critical to long term grassland health and resilience. Where soils are in poor condition, grasslands may be less productive and diverse.

Soils are also important ecosystems in their own right, hosting a huge diversity of living organisms.

Soil degradation can take the form of:

• Loss of topsoil due to erosion.

• Loss of organic matter (due to lower plant matter inputs), which reduces the amount of water and nutrients available to plants, and reduces how much carbon is stored in the soil. Organic matter is also important for soil structure, resilience to erosion and soil biology (microbes and soil animals).

• Poor soil structure. This could take the form of compaction (which hinders plant growth and reduces soil water storage) or lack of cohesion due to less organic matter, meaning soils are easily washed or blown away (soil erosion).

• Depleted soil biology (microbes and other soil fauna such as earthworms) can disrupt soil processes so, for example, less nutrients are available to plants, and less carbon is sequestration from the atmosphere.

Soil degradation can be slow and difficult to reverse, but there are ways that the condition of soils can be protected and improved...

Soil restoration approaches that are being investigated to see how effective they might be for savanna soils include:

• Reduced grazing intensities (lower stocking densities) to ensure plant cover is maintained and there is less pressure on the soil.

• Managing grazing differently, such as rotational grazing, where animals are grazed at a high density for a short duration, then moved on to a different area, allowing the soil and plants to recover before being grazed again at a later date.

• Increasing plant diversity by reseeding, or by grazing management as above. This can improve soil structure by increasing the diversity and density of plant roots, and stimulating soil microbes which play an important role in nutrient cycling.

• Using "inoculants" (small quantities of healthier soils or manures) to kick start soil biology.

• Using manures to add nutrients and organic matter to soil and improve structure.

Scientists at the International Livestock Research Institute (ILRI), Lancaster University, the University of Nairobi and the Technical University of Munich are undertaking research into savanna soils and plants, and how they can be restored to benefit grazing, biodiversity and climate resilience.

We are investigating soil restoration approaches such as those listed above to see how effective they might be for savanna soils include:

Much of this research is being done at ILRI's field station 60km south-east of Nairobi, called Kapiti.

As a working livestock ranch, Kapiti is an ideal site for research into soil restoration and grassland management, as well as other topics such as greenhouse gas emissions and livestock health.

Soils are naturally highly variable in the minerals they contain, their structure, drainage, nutrient holding capacity, and biology.

To be able to protect and restore soils, it is important to know the specific characteristics of the soils you are working with, as each will respond differently to management and restoration approaches.

Therefore the first step was to assess what soil types are present at Kapiti, and what condition they are in. Soil pits were dug across the ranch to assess soil type, with three main soil groups found:

The map below shows where this soil types are found across the ranch. Click on the soil types to see photographs and more information.

There map also contains results of a plant diversity survey carried out at 3 sites across the ranch. This baseline data aims to improve our understanding of the links between soil condition and vegetation and allow us to track how vegetation responds to, and recovers from, drought.

Now that we've mapped soil types, and carried out an initial survey of plant diversity, we're planning research under the following areas:

• How does vegetation recover from severe drought? We'll continue to assess plant cover and diversity in the same 3 areas to see how they recover following two years of severe drought.

• Can legumes improve drought resilience of grassland soils? Legumes and grasses are being grown in Kapiti soil in a greenhouse environment to see what impact different mixes have on soil biology, nutrients and soil moisture, under both drought and well watered conditions.

• How can topsoil regeneration be accelerated? Looking at strategies such as re-seeding with different species and incorportating animal manures to rebuild topsoil where this has been lost through erosion.

• How can grazing be managed to improve soil health, grassland productivity and drought resilience? Research into grazing strategies such as rotational grazing.

There are many areas of potential research and an increasing number of researchers interested in grassland soils, so we hope that this initial work at Kapiti sows the seeds for many more restoration and research projects!