In South Africa’s dryland farming systems, moisture conservation has become a key production strategy. As seasons become more erratic and dry spells become costlier, the ability to capture, store, and efficiently use rainfall may be the most important factor distinguishing resilient farms from vulnerable ones.
“This calls for a shift in thinking. The main question is no longer, ‘How much rain did we receive?’ but rather, ‘How much of that rain did the soil retain and make available to the crop?’” says Prof Nomali Ngobese, an associate professor in North-West University’s (NWU) Faculty of Natural and Agricultural Sciences.
South African farmers face not only the challenge of limited rainfall but also the challenge of rainfall loss. A significant portion of rainfall does not benefit the crop. Instead, it runs off the field, evaporates from exposed soil, and drains below the root zone.
“Each of these pathways represents lost opportunity. In dryland systems, this loss can mean the difference between a crop that survives stress and one that fails under tough conditions. Moisture conservation is, therefore, not just about sustainability; it is about making rainfall add to productivity,” explains Prof Jacques Berner, an associate professor in NWU’s Unit for Environmental Sciences and Management.
How water is lost
Water loss in cropping systems typically happens in three ways: run-off, evaporation, and deep drainage. Effective moisture conservation aims to reduce all three.
With run-off, water doesn’t enter the soil. When rainfall hits bare or compacted soil, infiltration is limited, and the water flows off the field instead of soaking into the root zone. The solution is to improve soil structure and maintain surface cover to boost infiltration.
Evaporation means water is lost to the atmosphere. Bare soil warms up quickly, speeding up evaporation and leading to significant moisture loss, especially early in the season. The answer to this problem is keeping crop residues or mulch on the soil surface to serve as a protective layer, reducing temperature swings and slowing evaporation.
Water that moves below the root zone is no longer available to the crop. This calls for the improvement of soil organic matter and structure to enhance the soil’s water-holding capacity within the root zone, reducing losses to deep drainage.
Another issue affecting water retention is soil compaction.
“Soil compaction is one of the most overlooked threats to moisture conservation. Compacted soils restrict water infiltration, limit root growth, and reduce access to stored soil moisture. The result is a double loss, as less water enters the soil and less of what is stored is available to the plant,” explains Berner.
He adds that soil compaction can be avoided by eliminating traffic on wet soils, reducing unnecessary tillage, and including crop rotation with deep-rooted crops.
“A field does not need more rain if it is already wasting what it gets. The first step in moisture conservation is ensuring that water enters and stays in the soil. This depends on good soil structure, adequate organic matter, active soil biology, and surface cover,” adds Ngobese.
No-till is a system, not a shortcut
Practices linked to conservation agriculture, such as reduced tillage, residue retention, and crop rotation, help improve rainfall capture.
No-till is often seen as a quick fix. In reality, though, it is part of a broader system that needs time and consistency. In some cases, conventionally tilled soils may appear to perform better early in the season.
However, research shows that under semi-arid conditions, conventional production systems may hold more moisture initially, while reduced tillage systems often retain more moisture later in the production season.
This matters because yield is most affected during stress periods, especially during the flowering and grain filling stages of crop growth. The real value of reduced disturbance lies in the soil’s ability to sustain crops during these critical stages.
Moisture conservation is a risk management strategy
Farmers often gauge success based on early crop establishment. However, a well-established crop can still fail later in the season due to a lack of soil moisture.
Moisture conservation isn’t only about maximising yield in ideal conditions; it’s about reducing risk in dry years, improving yield stability over time, and enhancing the efficient use of nutrients. In this sense, moisture conservation is not just an agronomic decision but also a financial strategy.
Ngobese and Berner recommend five practical ways to retain more moisture in the root zone:
- Keep the soil covered: retain crop residues or apply mulch to reduce evaporation and protect soil structure.
- Minimise soil disturbance: reduce tillage to maintain soil structure.
- Avoid compaction: manage traffic and avoid working on wet soils.
- Improve the soil’s water-holding capacity and resilience: build soil organic matter.
- Focus on the full season: evaluate success based on crop performance under stress and not just on early growth.
The cheapest water storage on the farm
Farmers can’t control how much rain falls, but they can manage how much of it is retained in the soil and used effectively. In an unpredictable climate, the most reliable form of water storage is not a dam or an irrigation system but the soil itself.
Every improvement in soil structure, cover, and management increases the amount of rainfall and irrigation water that contributes to yield. Over time, this leads to more stable production, reduced vulnerability, and improved profitability. In dryland farming, every millimetre of rain counts, but only if the soil retains it.
Email Prof Nomali Ngobese at [email protected], or Prof Jacques Berner at [email protected].
