Dr Tilahun Amede is the Head of Resilience, Climate and Soil Fertility at Alliance for a Green Revolution in Africa.
He spoke to Seeds of Gold on how to address the problem of soil salinisation and why it has become rampant in Kenya and many other countries across Africa
What is soil salinisation and what causes it?
Salination is a form of degradation due to excessive accumulation of water-soluble salts, which either exist naturally in the soil or because of poor agriculture practices. In coastal areas, ocean overflow and associated swamps, are a common cause of salinisation.
This drives up the soil pH above the 5.5 to 7.5 optimum range, which hampers its ability to grow food crops. Soil salinisation is a major challenge and a threat to food production globally, particularly in arid and semi-arid regions.
Salinisation is mainly caused by drought conditions or poor irrigation practices. In dry areas, heat causes water to evaporate, leading to concentration of salt around the surface. Irrigation using ground water that is saline, on the other hand, leads to accumulation of salts in the soil surface over time. With effects of climate change, drought is more prevalent, intense and frequent, thus necessitating irrigation and hence the risk of salinisation.
How does a farmer know their soils are saline or not?
It is difficult to physically see soil is saline except in acute cases where white crusts occur on the surface. Crops growing in salinated soils could wilt or get stunted even under good soil water regimes. Farmers need to get their soils routinely tested to ascertain the pH and correct it before it gets out of hand.
Unfortunately, once soils are saline, there is no quick fix. It can be mitigated, for instance, by growing legumes which fix nitrogen for consecutive years and release ions into the soil, reducing pH. Conservation agriculture methods such as crop rotation, use of organic fertiliser and good irrigation practices are important in preventing salinisation.
What are the disadvantages of having saline soils?
Saline soils reduce the ability of crops to take up water and limit the availability of micro-nutrients that are important for crops to grow, leading to decreased productivity. They also concentrate toxic ions that are harmful to plants and other beneficial micro-organisms. The soils may also remain crusted with salt and difficult to plough. In general, salinity affects the overall profitability of farms.
There has been a long-held belief that increased (mis)use of inorganic fertilisers have contributed to saline soils, is that a fact or a myth?
While inorganic fertiliser is not the major source of salinity, excessive use of certain fertilisers, such as potassium chloride or ammonium sulfate has been found to cause salinisation. Several other factors have been linked to salinisation including increased frequency and intensity of drought, poor irrigation practices, population pressures leading to destruction of wetlands and other ecosystem for farming.
Soils in Africa have been described as mostly saline. Is that the case?
Globally, the Food and Agriculture Organisation estimates that there are more than 833 million hectares of saline soils, with salinisation taking up to 1.5 million hectares of farmland from production every year. In Africa, about 30 per cent of the soils are considered to be saline.
This is a huge threat to food production for a continent that is struggling to feed itself. The Great Rift Valley, which includes Kenya, have soils of volcanic origin, but also are located in arid and semi-arid areas where precipitation is insufficient to drain the soluble salts contained in the soil profile. Hence, the risk of increasing salinity in the region is high with the rising threat of climate change.
With most soils in Africa becoming saline, what is the continent's future when it comes to food production?
We need to adopt sustainable farming to maintain healthy ecosystems and ensure that salinisation does not occur. This includes improved management of irrigation schemes, increased use of organic fertiliser, diversifying our production towards less sensitive crops like sorghum, millet and barley.
Irrigation needs to strike a balance in as far as water management is concerned, using not more than is required. Crop rotation ensures that there are different crops with different nutrient needs, thus boosting soil health. We can only end hunger and poverty in Africa through resilient food systems, which start with healthy soils.
With Africa’s population set to double by 2050, all of us need to minimise the damage to human health, and the environment.
Conservation agriculture needs to be promoted, as appropriate, including agricultural practices that improve and strengthen soil structure, increase water retention, and reduce production costs while improving crop yields.