Rising to the challenge

Ways in which growers can maintain productivity and profitability in spite of water scarcity. By Anna Mouton.

Agronomist Siziphiwe Dinwa of Dutoit Agri is engaged in yield estimation and precision agriculture. Part of her job is applying new technologies to improve irrigation efficiency and water productivity. She works on different fruit types at multiple sites, mostly across the Western Cape. Fresh Quarterly spoke to her to learn how growers can best manage their water, and why she is excited to be in agriculture.

Back to basics

“I think one of the most important things is to focus on irrigation scheduling, and what the need of the crop is at a specific physiological stage,” says Dinwa. She points out that a lot of irrigation water can be lost through run-off, as well as through deep drainage, which occurs when water drains to soil below the root zone. Over-irrigation also creates an unhealthy environment for roots by saturating the soil.

Dinwa explains that decisions about scheduling start with mapping the soil. One important reason to map the soil is to determine representative locations for measuring soil moisture. Soil conditions may also be so variable that different areas within an orchard cannot be irrigated according to the same schedule. It may be necessary to split the irrigation system, says Dinwa.

When measuring soil moisture, there are benefits to both traditional methods, like subjective assessment of soil sampled from profile holes, and modern technology, like moisture probes that link to the cloud. “The two systems work well together, and information from field observations can be correlated to the probe graphs,” states Dinwa. “And if there is a system failure, it’s always good to have two systems that run hand in hand.”

Another data source is the weather — the higher the temperature, the greater the atmospheric demand and therefore the irrigation requirement. Automated systems tend to draw on soil dynamics more than on weather data, and need interpretation by growers and their irrigation specialist. But automation can help to run irrigation more smoothly, especially if growers understand the system well and know how to troubleshoot it.

“Some farms are completely automated,” says Dinwa. “Some are not automated at all — they still use the traditional methods, and they manage to irrigate efficiently.” The important thing is for growers to understand their soils, their crop water requirements, and the microclimates on their farms. They need to stay on top of their scheduling, especially during periods of extreme weather conditions such as heatwaves.

The drip revolution

Although micro-irrigation is a big improvement over flood irrigation, Dinwa points out that it can still be wasteful due to high evaporative losses. In contrast, drip irrigation is applied directly to the soil, leading to better penetration and spread. “Drip has been found to be about 30% more efficient than micro-irrigation,” she says. “Even international literature is showing us the benefits of drip irrigation.”

Fertigation — the use of irrigation to apply fertiliser — is another advantage of drip irrigation. Fertigation offers more control and precision than flat-rate application by a tractor.

Dinwa is convinced that drip irrigation is the future, but she cautions that the design has to be correct. For example, she says that many growers have burnt their fingers because of using a single instead of a double drip-line, resulting in insufficient spread of water and reduced yields.

She adds that double drip-lines are easily adaptable to different planting densities, and water delivery can easily be adjusted for different soil types.

“Drip irrigation has evolved immensely, and going forward we can expect more adoption of drip irrigation by South African farmers,” reflects Dinwa. “However, the technology is not cheap, so not all farmers of different scales can afford it right now.” But even though drip irrigation gets very expensive very quickly, Dinwa believes that it’s a worthwhile investment.

Objections to drip irrigation are sometimes raised due to its perceived incompatibility with cover crops. There’s still a lot to learn about this issue, but Dinwa says that the key is to be clear about your objectives, and design the system accordingly. “Even with drip irrigation you can control the tempo, the spread, and just how much water you’re giving and for how long, so some water naturally moves to the cover crop.”

More ways to save water

Besides concentrating on correct application of water, efficiency can also be improved by reducing evaporation. This is especially relevant to young blocks, which Dinwa recommends should be mulched. She considers mulches and cover crops useful not only for reducing evaporative losses, but also for suppressing water-guzzling weeds.

Nets may likewise reduce water losses through reducing evapotranspiration, alongside all the other gains in terms of protecting fruit against the elements.

Dinwa reports that some farmers attempt to save water by irrigating at night to reduce evaporation while ensuring that trees have ample opportunity to take up the water. However, she believes that it is better to irrigate during the hottest time of the day when atmospheric demand and plant water needs are highest.

“Another way in which farmers have adapted to using water more efficiently, is using different rootstocks and different training systems,” says Dinwa. “Trees don’t look the way they used to, and they’re not going to have the same water demand, and all that trickles down to irrigation.”

High-density plantings on dwarfing rootstocks create the opportunity to produce more fruit per unit land and per unit water, which is critical for a dry country like South Africa, especially considering the realities of climate change. “We need to use our limited supply of water more efficiently, meaning we need to produce more and better-quality fruit with the same or less water – more crop per drop,” emphasises Dinwa.

She sees the potential of new technologies such as satellite imagery and drone mapping contributing to a better understanding of the variation in orchards. “Understanding variation will allow us to be proactive in saying, this is what we’re seeing, this is what’s being predicted by climate scientists, and these are the solutions we should start implementing right now.”

In spite of the challenges and obstacles facing growers, Dinwa is optimistic. “I guess that’s why I’m in this industry, because it’s so exciting — I get excited by these challenges. These challenges keep everyone awake at night, but at the same time drive us to solutions to the betterment of our industry.”

Image supplied by Siziphiwe Dinwa.