“We still have scope to adapt our land management”

The slogan for World Soil Day on 5 December 2023 sounds a bit banal: “Soil and water, a source of life”. But the statistics make you sit up and take notice. And behind the numbers is a dramatic development that has barely registered with the public. “We urgently need to foster discussions at all levels about why and how we use soil and water,” says CDE scientist Tatenda Lemann.

Tatenda Lemann
“Our top priority must be to make sure that erosion doesn’t even begin to develop”: Tatenda Lemann. Photo: IISD / ENB, Matthew TenBruggencate

Interview: Gaby Allheilig

As a scientist, you focus on soil and water. Do you also have a personal connection to soils?

We all have a connection to soils, though we usually aren’t aware of it – for example, through the food we eat. I personally became properly aware of it when I first witnessed how the topsoil of fields without vegetation cover was simply washed away in a heavy rainstorm. Later, during my dissertation, I took a closer look at how much soil in the Ethiopian Highlands is washed away depending on the form of land use.

How much was it?

In a catchment measuring 5,000 hectares, for example, we measured that about 100,000 tonnes of soil were washed away into the river in a single year – equal to about 2,500 lorries full of earth. That’s an average of over 20 tonnes per hectare. And this is a catchment that also has forests, so the numbers were much higher on individual cultivated fields. The results of this erosion are clearly visible in the Blue Nile during the rainy season: the river turns brown and carries away tonnes and tonnes of fertile soil. With that, the uppermost, nutrient-rich layer of soil is lost from the catchment and crop yields decline. Meanwhile, the erosion also impacts infrastructure such as dams further downstream.

Blue Nile during the rain season
Tonnes of fertile soil are washed away: The Blue Nile during the rainy season. Photo: Tatenda Lemann


“Worldwide, about 95 percent of our food comes directly or indirectly from soils”


Does increasing soil erosion pose a threat to our food supply?

Worldwide, about 95 percent of our food comes directly from soils – namely, from the top 40- to 50-centimetre layer. Between 80 and 90 per cent of all life on Earth depends on this layer of soil. That said, it doesn’t take long for soils to be washed away, eroded, salinized, or chemically or biologically degraded. It can result from a single event or from years of degradation. But rebuilding just one centimetre of healthy soil takes anywhere from 100 to 300 years, depending on the climatic zone. So, when soils are washed away or degraded, it obviously has a major impact on agriculture and our food chains. But it also affects biodiversity and the climate. This is because soils can store a lot of carbon, which they can then also release back – thereby further fuelling global warming. In addition, soils are important stores of water. They can prevent flooding and make the water they absorb available to plants during dry periods.


“If we carry on like this, 4060 years from now we won’t be able to feed the global population”


Staying on the topic of soil fertility: It’s possible to apply fertilizer, of course.

Indeed, you can compensate for a lot with fertilizers in the short term. But this doesn’t work forever – especially if it’s artificial fertilizer – and it doesn’t stop the degradation of soils. Additionally, it has negative consequences for biodiversity and water quality. Statistics show that fertilizer use per hectare continues to rise at the global level, despite recent declines in individual countries like Switzerland or Germany. If we take into account biodiversity loss, some studies suggest we only have 80 to 120 more harvests remaining based on current intensive land use and widespread monocultures. This means that if we carry on like this, 40 to 60 years from now we won’t be able to produce nearly enough to feed the global population.


“Land degradation impacts us everywhere – even in Switzerland”


In October, the UN Convention to Combat Desertification (UNCCD) announced: “If current trends persist, we will need to restore 1.5 billion hectares of degraded land by 2030”. How do you see it?

Things really don’t look good and the trend is definitely still going in the wrong direction. The global extent of land degradation is estimated at 20 to 40 per cent of the total land area, directly affecting almost half of the world’s population and spanning the world’s croplands, drylands, wetlands, forests, and grasslands. This was also highlighted by the UNCCD’s Global Land Outlook.

The UNCCD is the only international agreement focusing globally on land conservation. Unfortunately, it still receives far less attention than the other two Rio conventions on climate and biodiversity. I think this might be because of the somewhat unlucky choice of the word “desertification”. In our agroclimatic zones, many people assume it doesn’t concern them, as the nearest desert is far away. But the UNCCD is actually about degradation of land, which includes soil, water, and vegetation; or rather about preventing or reversing it. That impacts us everywhere – even in Switzerland.

How strongly does it affect Switzerland?

Depending on the data source, almost 10 percent of Switzerland’s total land area is degraded and around 20 percent of arable land is considered at risk of erosion. In addition, droughts and flooding – two major drivers of land degradation – are increasing here, too. We have to react.


The UNCCD emphasizes the following responses, in this order: prevent land degradation, reduce erosion, and restore soils. Because the effort required to reverse something is much greater than that of preventing harm in the first place, at our latitudes when using land we need to focus on making sure that erosion doesn’t even begin to develop.

What does that mean in concrete terms?

For example, we need to ask ourselves: Are we going to continue to cultivate our crops intensively on “bare” land, or are we going to increase our land cover so that the soils don’t dry out? Are we going to use more and more fertilizer, endangering our biodiversity and drinking water, or will we switch to more sustainable cultivation methods? Are we going to irrigate our fields until our rivers run dry or will we begin to grow crops that require less water? We still have the choice and the scope to change our land management and to adapt to climate change.


“Interest in taking measures has increased in some regions”


You recently participated in an international meeting that assessed the progress of different countries in implementing the UNCCD Convention…

It’s called the Committee for the Review of the Implementation of the Convention (CRIC). It meets every year to discuss countries’ reports of where they stand and what they have achieved. This year, we saw that not all countries that had set targets for land degradation had issued reports for the most recent period. And there were major differences in reporting quality between the countries that did report.

Does this mean that little or nothing is being done?

No, things are happening, even if it’s not enough. At least in some regions, there is growing interest in monitoring land degradation at the national level and in taking measures to prevent, slow, or reverse it. At the CRIC in Samarkand in November, we talked for the first time not only about methods and indicators, but also about results. There is now a UNCCD data dashboard (see box) that illustrates what countries reported and shows the global status of degradation. This transparency makes the Convention more accessible and enables us to look for ways of improving global communication and emphasizing the severity of the situation.

Discussion with Tatenda Lemann at the CRIC in Samarkand
How can local knowledge from civil society and NGOs be linked to national reporting? Discussion with Tatenda Lemann at the CRIC in Samarkand. Photo: Jean-Marc Sinnassamy

What is your role in the country reporting?

With WOCAT, a global network for sustainable land management, we have provided support to individual countries in assessing land degradation for their reports. Using cloud computing, we worked with different stakeholders to develop easy-to-use apps that integrate global, national, and local data and knowledge. This enables countries to verify the standardized global data against their national and local knowledge and helps them to understand where the degradation hotspots are and what is fuelling them.


“A lot of knowledge exists about innovation and best practices”


So, an app will fix things?

Not by itself, of course! But, to address a problem, you first have to identify, understand, and accept it. An app in the form of a geospatial platform helps to bring together different stakeholders – for example, ministries, planning or biodiversity experts, farmer cooperatives, nongovernmental and civil-society organizations, and scientists – and to facilitate a joint discussion and negotiation of what is locally and nationally relevant. That is crucial in order to determine what’s actually needed and, in a second step, to decide what measures make the most sense and where they should be implemented. The necessary knowledge exists. This is evidenced by all the farmer innovations and proven good practices recorded in the WOCAT database. This global database for sustainable land management already contains over 2,300 good practices from 136 countries. We are working to scale up this knowledge and promote its exchange.

What are the hurdles when it comes to sharing knowledge and providing advice on sustainable land management?

It varies greatly from region to region. An important factor is the type of agricultural extension services offered and who they are provided by. In Switzerland, for example, agricultural companies play a big role. As long as the advice mainly follows monetary interests, it remains difficult to advance sustainable solutions that are both socioeconomically and ecologically relevant. But that’s exactly what’s needed. We must adjust to the new realities that come with global change. This doesn’t only apply to agriculture. We need to foster discussion of why and how we use soils and water at every level – in politics, business, and society. If we wait, it will lead to conflicts – even in Switzerland. And such conflicts are notoriously hard to resolve once they’ve broken out.


In addition to combating desertification, drought, and land degradation, the UNCCD seeks to restore ecosystems. The aim is to strengthen the resilience of land to global warming as well as to prevent loss of biodiversity. The second global report on the status of land resources, titled “Global Land Outlook 2”, was published in 2022.

WOCAT – Global network on sustainable land management

The World Overview of Conservation Approaches and Technologies (WOCAT) is a global network founded in 1992. Its aim is to improve land resources, ecosystems, and people’s livelihoods. It strives to achieve this by sharing, enhancing, and applying knowledge about sustainable land management. CDE belongs to the executive team of WOCAT and plays a key role as a founding member. The WOCAT consortium comprises seven partners: CDE, FAO, ISRIC, GIZ, Alliance CIAT-Biodiversity, ICIMOD, and ICARDA.