In a 2018 study by the CSIR, focussing on the water use and requirements of apples trees, research team leader, Dr Sebinasi Dzikiti, says that apple trees in a high production orchard drink between 80 and 136 glasses of water a day. This equates to 30 000 to 45 000 litres per hectare per day, depending on leaf area. He does however emphasise that this is very complex, and that the calculation depends on a variety of factors.
One determining factor contributing to total orchard water use, is evaporation from the orchard floor. Dzikiti explains that the greater the area of orchard floor wetted during irrigation, the greater the potential evaporation water loss. This is, according to him, one of the reasons why drip irrigation is more effective than micro-sprinkler irrigation.
Dzikiti says that improved irrigation practices are required to assist apple producers in limiting losses and therefore lowering orchard water use. He calls for the use of water saving techniques such as:
- Planned irrigation scheduling;
- Drip irrigation to reduce evaporation from the orchard floor;
- Shade nets to reduce evaporation and tree transpiration; and
- Choosing dwarfing rootstocks to reduce unnecessary shoot growth.
“By implementing methods such as these, producers can get more fruit with less water. It’s all about effective orchard management.”
Drip can do it
According to Abie Vorster, agronomist at Netafim South Africa, there is a misconception that drip irrigation does not work in apple orchards. “It is true that drip irrigation has failed in many apple orchards. There has, however, also been many cases where it has brought great success. The difference in outcome can often be drawn back to one factor – irrigation scheduling.”
He says that micro-sprinkler irrigation is most commonly used in apple orchards. “Changing trends in tree spacing and row widths, as well as increasing pressure to lower water use, are forcing the industry to revisit the way they irrigate. Drip irrigation offers the solution.”
Producers must make a paradigm shift when they convert from micro sprinkler to drip irrigation. “It is very important that a new scheduling strategy accompany this shift,” Abie warns.
As drip irrigation delivers less water at a time, compared to micro-sprinkler irrigation, it often results in under-irrigation when scheduling is not adjusted. Over-irrigation also occurs when scheduling is wrongly adjusted. “Because water delivery is lower and less visible with drip irrigation, there is a misconception that drip irrigation do not deliver enough water. This prompts producers to increase their irrigation volumes and resulting in over-irrigation.”
Abie encourages apple producers who are considering or implementing drip irrigation, to not go at it alone. They are advised to rather involve a drip irrigation expert in the process, to make sure that their irrigation scheduling is spot-on. “Drip irrigation works extremely well in other crops, and can work in apple orchards, if it is properly managed.”
More control, better results
Drip irrigation allows producers to apply precise and uniform amounts of water and nutrients directly to the root zone of plants. A smaller area is wetted, which means that the potential for water loss is lower. Drip irrigation achieves high yields with lower water use. Beyond this, it also lowers dependency on weather circumstances, allowing for greater control over yields.
Abie explains that the greatest benefit of drip irrigation – and the reason why the apple industry needs it – is that it offers greater control over the amount of water delivered.
“The reality is that the apple industry is increasingly moving towards higher density plantings with narrower row and tree spacing. In the past a micro-sprinkler at every, or every second, tree would do the trick. But with higher tree densities, the delivery rate of micro-sprinklers becomes too high and runoff occurs.”
Scheduling is key
Drip irrigation, according to Abie, solves this problem, as the lower delivery rates of drip irrigation makes it possible to irrigate efficiently in such high-density orchards. “This allows you to efficiently manage your water source and water delivery. In turn, it gives you greater control over a host of other factors including fertigation, labour requirements, time spent on irrigation management and more.”
Abie reminds that the success of drip irrigation in apple orchards greatly depends on scheduling, which, of course, will differ from orchard to orchard. A general movement towards low flow drippers is however evident.
“I cannot emphasise enough how important it is to bring in an expert to develop the correct scheduling strategy for your orchard. As mentioned, drip irrigation and lower delivery rates give you greater control over irrigation. Use this control to your benefit by involving the necessary expertise and following the correct strategy.”
A necessary shift
“I believe that, given current trends, very few apple producers will be able to move and grow with developments, without shifting to drip irrigation. Remember, the bulk of South African apples are grown in the Western Cape where water scarcity and water use limitations are at its worst.”
As is the case in most of agriculture, apple producers have a responsibility to use water more efficiently in food production. Drip irrigation makes this possible. – Netafim