Water use in Japanese plums

New project aims to inform optimal resource management. By Anna Mouton.

“Our agriculture for centuries has been based on extensive agriculture because we have enough land. So up to recently we never really thought about optimising land use and water use,” says Dr Nebo Jovanovic of the hydrosciences research group at the Council for Scientific and Industrial Research.

Jovanovic holds that our approach has to change for agriculture to remain viable in a warming world where water is becoming an ever-scarcer resource. “I’m a very big supporter of intensive agriculture. In my mind it’s more sustainable because you are using resources in a more efficient way, and you can control them better.”

A new project led by Jovanovic and co-funded by the Water Research Commission and Hortgro Stone will aim to measure the water requirements of high-performing Japanese plums. “The plum industry is growing and it’s becoming more and more intensive so we need to know how much these orchards use in a season so you can allocate water,” explains Jovanovic.

“If we don’t plan for water allocation there are going to be risks, especially now that the forecast is for more and more droughts in future.”

Getting the complete picture

The new project will examine water use in full-bearing African Delight and Fortune plum orchards in Robertson and Wellington. Representative trees will be monitored over the course of the season to establish their water requirements during different growth stages.

“The plan is to do the first season of experiments in Robertson and the second one in Wellington,” says Jovanovic. “But we will try and keep some of the instrumentation at the first site for longer. It’s always good practice to have long time series of data because one can learn a lot from different years.”

Jovanovic explains that they will be analysing the plant, the soil, and the atmosphere to gain a complete picture of water movement. Measuring the whole system is labour-intensive, not least because equipment installed in orchards needs to be checked regularly. “You won’t believe all the things that can happen in the field with animals,” he says. “A common problem is chewing of wires.”

Manual measurements remain important even when data loggers are in place. Jovanovic cites the example of soil. “The problem is that soil is very variable even within an orchard. Many times it’s preferable to have a manual instrument where you can take a lot of measurements instead of having a single probe that gives you a lot of data but only at one place.”

A post-graduate student is due to start work soon and will be preparing to begin measurements in spring. The project runs until 2024.

Putting drip to the test

Agriculture accounts for about 60% of water use in South Africa. “People are very often carried away by these figures, but one needs to put it into perspective,” states Jovanovic. First of all, it’s a big industry, it creates jobs and income, and it produces food. And it doesn’t mean that it’s going to use more water than something else.”

Jovanovic points out that even open veld uses water. “We have measured around the Western Cape that sometimes natural veld uses more water than agricultural land, in some circumstances, because fynbos is evergreen.” Natural vegetation also has a deeper rooting system than many crops.

Irrigation is the main water use in agriculture. One of the objectives of the new project is to compare drip irrigation with microsprinklers. Drip irrigation is considered to be more efficient than microsprinklers because the watered area is smaller with drip irrigation. Microsprinklers wet a larger area but some of this water evaporates unproductively.

Jovanovic believes that drip irrigation can provide savings of 10%–20%. Greater efficiencies in water use translate into financial gains and are an essential part of intensifying production. “The orchards of the future — the vision of Hortgro — are super-intensive orchards that are more manageable and higher producing, but under the assumption that they use resources in an optimum way. The water is used optimally on a smaller area but there is the opportunity also to use more water in other areas.”

Water is increasingly in short supply as the world warms. Research that informs more efficient water use is essential to ensuring a sustainable future for agriculture — and ultimately for all of us.

What are people saying about this research?

Charl Stander | Franschhoek Marketing

“We want to know the critical minimum water requirement that will enable a good harvest under water-limited conditions. One reason is that we want to use water efficiently and not waste it. The other reason is that we want to demonstrate that we need a certain amount of water to produce a good harvest. We want to provide evidence that fruit size and quality will suffer and that trees will decline if they do not receive this amount of water. That will assist us when negotiating water allocations.

“It’s also important to recognise that your irrigation system is a function of soil type — the water-holding capacity of your soil — as well as commodity and cultivar. Drip irrigation is not the best solution for all situations. Examples where drip irrigation might not be ideal include plums on Marianna rootstocks and late cultivars under dry conditions.”