Pictured Above: An irrigation strategy that takes the weather forecast into account should be developed to guard against tree stress during hotter days.

Experts agree that while El Niño is expected to make landfall in South Africa mid-summer, if macadamia farmers prepare now, they could mitigate the impact of the drier weather in their orchards.

The last time South Africa experienced an El Niño, macadamia yields dropped as flowers wilted in the heat and trees shed nuts when they ran out of reserves. While the severity of the El Niño headed our way this year is still uncertain, farmers are advised to take precautions to prevent a repeat of the 2015 and 2016 season.

Barry Christie, group agricultural technical manager at Green Farms Nut Company, said while there is little that can be done when temperatures soar and rain is scarce, there are practices farmers can follow to assist with moisture retention and to reduce evaporation. These practices will decrease the stress on the trees on hotter days.

Christie advises farmers to start building a mulch layer in the orchard early on to make sure there is sufficient organic material to protect the soil. “The mulch keeps the soil surface temperatures far lower than what they would be if the soil were bare. It also prevents all of the water from evaporating or running away,” he said

Added to that, not skirting the trees too high off the ground to allow for deeper shade on the soil and around the roots would keep that zone cool, he added.

Digging a profile hole in the orchard is the best way to determine water flow and irrigation cycle lengths.

Watch the weather

An irrigation strategy for hotter days is vital to ensure the trees are not under undue strain, whether from too much or too little water.

Netafim agronomist Jovan Erasmus said when temperatures peak, farmers might be inclined to increase irrigation cycles. “The water used by the trees is determined by several factors: temperature, humidity, wind, and radiation. These all affect the rate at which the tree transpires, and how much water it then needs. It makes sense that trees will use more water when it’s hot, but they do reach a point when they shut down completely and don’t take up a single drop more. If there is then too much water in the root zone that is not going anywhere, it deprives the tree’s roots of oxygen. This can be as detrimental as not receiving enough water in the first place,” he said.

Erasmus urges farmers to monitor weather conditions, and when peak temperatures are expected, the irrigation cycle should be prolonged on the day before the predictions.

“Ideal irrigation schedules should consist of daily short and weekly longer cycles. Short cycles to wet the top 300mm of soil where the roots lie, and a longer cycle to reach as deep as 600mm, which is referred to as the buffer zone. This way, the roots are not consistently deprived of oxygen, and a water reserve is available for when the tree needs it. It is these longer cycles that should be employed the day before temperatures are set to spike.”

Optimal irrigation requires consideration where all soil types and filtration rates are taken into account. It is important, then, for farmers to understand how long each cycle should be to wet the respective areas, without depriving the tree of water or oxygen. Digging a profile hole in the orchard and monitoring how deep the water reaches during irrigation cycles is advised.

El Niño could spell disaster if high temperatures persist during low rainfall. But steps taken now to prepare the orchard floor and understand water management can bring relief.