In sub–Saharan Africa, droughts are common. In fact, the frequency of droughts in the region has almost tripled from 2010 to 2019, affecting nearly 115 million people. Even with these climatic changes, the region still relies mainly on rainfall for irrigation. By the end of the century, it is projected that all crop yields could decrease by between 15 and 20% in sub-Saharan Africa (World Bank Group, 2021).

The decrease in rainfall and potential decrease in food production highlights the importance of irrigation and using water efficiently. At times, rainfall cannot provide the required water for sustained growth and production of crops; or there are unequal water resources and water scarcity. As a result, Farmers need a man-made supply of water to land for production of crops through furrows, canals, channels, or pipelines. Alternatively, farmers use rainwater collected from containers and roofs of farm buildings.

Irrigation systems that distribute a controlled amount of water can secure uninterrupted agriculture production caused by irregular, insufficient or uncertain rain. When water is used efficiently through irrigation, agricultural yields have the potential to increase by at least 50%. Sustainable irrigation does not only contribute to increased crop production but also reduce variability in yield through improved control of the crop environment. This efficient use of Irrigation is well placed to build climate change resilience, for improved food security and nutrition, and poverty reduction.

WE4F Southern and Central Africa Communications and Knowledge Management Specialist, Tebogo Masombuka, interviewed Agricultural Water Expert, Dr Manuel Magombeyi, about key information, best practices, and efficient water use when irrigating.

Why use irrigation and not just rainfall?

Irrigation supports agricultural production. In the most vulnerable parts of Africa, irrigated agriculture means that farmers can extend the growing season(s), increase productivity and incomes, and improve their livelihoods. Also, it is a climate change adaptation strategy because of the importance of water in agricultural production and subsequently in food security. According to the World Bank, irrigated agriculture is, on average, at least twice as productive per unit of land as rainfed agriculture. This means that the precious water used when irrigating with proper systems allows for more production intensification and crop diversification.

What is irrigation water-use efficiency?

It is the amount of water that is used by a crop to produce its yield in the field compared to the water that is diverted and channeled from the source to the field. Sources can be a stream, borehole, dam, or effluent from wastewater treatment plants.

What are the most common misconceptions about water-use efficiency in irrigation?

Water-use efficiency is normally confused with water productivity. Water-use efficiency describes the crops’ effectiveness in using the water supplied to the field. Water productivity is the mass of the crop yield, or the monetary value of the crop yield produced from water used/consumed by the crops.

Why should farmers and businesses care about irrigation water-use efficiency?

As the global population grows and water availability becomes more variable, efficient irrigation is crucial for producing more food with less water. Farmers should be determined to better use their resources.

Water efficient irrigation allows farmers to:

• use less water to grow the same quantity of crops on the same piece of land
• more productively farm larger areas of land while using the same amount of water; or
• use the same amount of water to grow higher value, more water-intensive crops
• reduce energy needs for transporting irrigation water
• reduce nutrient loss by leaching and surface runoff

Efficient irrigation, when compared with conventional irrigation methods, has significant benefits to the environment. Under sprinkler and drip methods of irrigation one can:

• reduce up to 25% of irrigation water
• reduce up to 40% greenhouse gas emissions
• reduce soil erosion
• reduce irrigation costs

What are the factors affecting irrigation efficiency?

There are a couple of factors that affect irrigation efficiency:

1. Efficient irrigation depends on a balance between the atmospheric and soil conditions.
2. Atmospheric precipitation and evaporation play important roles as do the water-holding characteristics of the soil. High precipitation and evaporation results in low water-use efficiency because more water is lost to the atmosphere. Sandy soils that have low water holding capacity results in less water available for the crop and low efficiency, while loamy and clay soils with high water holding capacity result in more water available for use by the crop, resulting in high water-use efficiency.
3. Type of irrigation method (furrow, drip, sprinkler), time of irrigation also affects irrigation efficiency. Drip irrigation uses less water to satisfy crop water needs, and is the most efficient of the three types, as water is applied close to the crop root, and not all over the field, minimizing evaporation and runoff.
4. Crop management practices – conservation tillage, planting densities, and improved varieties and pest control will affect crop productivity and water use. Conservation tillage practice is any tillage and planting system that covers 30% or more of the soil surface with crop residue, after planting, to reduce soil erosion by water and wind, and to allow water to infiltrate into the soil to promote economic and environmental benefits. Conventional tillage, such as moldboard plowing, leaves the soil surface bare and loosens soil particles, making them susceptible to the erosive forces of wind and water.

How can farmers and businesses improve their irrigation efficiency?

There are a couple of things that can be done:

• Change farming practices to include crop rotation (plant crops according to seasons and soil conditions) and conservation tillage (leaving a previous year’s crop residue on the field to reduce soil erosion and runoff) that help improve soil moisture conservation.
• Avoid over or under application of irrigation water
• Measuring soil moisture by a probe or sensor helps to assess how much water should be applied in the field and adjust irrigation scheduling based on soil and crop conditions
• Irrigate less than the required amount, during certain crop stages, this is known as deficit irrigation
• Improve distribution uniformity by making sure that nozzles are not excessively worn or clogged, and avoid irrigation with sprinkler when it is windy
• Apply supplemental irrigation to crops during rainy season to bridge dry days
• Timeously carry out regular and periodic maintenance activities to reduce water leaks
• Irrigate at times when it is not very hot, such as early morning, unless in very hot days where the irrigation cools the plants
• Shifting to less thirstier plants (e.g., shifting from maize to small grains, like sorghum)