Irrigation and Water Management During Flowering

By Theunis Smit, White River

Macadamias, and many other fruit trees tend to flower in spring, a season which is characterized by moderate temperatures, varying degrees of wind and more often than not a significant lack in rainfall.  Not only is rain scarce during spring, it is also the driest part of the year considering that rain during winter is either limited or completely lacking. Fortunately, most farmers have some water available for irrigation, the real problem is, however, how to manage the limited amount of water that you have during this critical time?

Before answering the million-dollar question, we need to consider some biological traits of macadamias that will dictate how water should be managed. Firstly, and most importantly, macadamias have a shallow root system, with a large portion of the roots being in the top 30-40 cm of the soil. Secondly, research has shown that macadamias are very efficient at taking water from the soil when it is available. Lastly, macadamias and many other crops get stressed when they are over irrigated, mainly due to the lack of oxygen in the soil. 

That being considered, during flowering the tree and its environment requires more water than most of the other parts of the production cycle. So how do you manage irrigation during the flowering period, considering that we especially don’t want trees to stress during flowering?

  1. If water is available, provide the trees with one long cycle of irrigation to increase the overall soil moisture content – Use irrigation scheduling probes to make sure the soil profile is filled.
  2. Following the long irrigation cycle, irrigate short cycles of irrigation more frequently. For example, if the plan is to provide the trees with 400 liters of water during the week, it is better to apply 100 liters four times per week than applying 400 liters in one go – This is essential when considering that macadamias have an extensive, but shallow root system.
  3. Under no circumstances should irrigation be increased to unreasonable amounts (i.e. 50 – 60 mm per week) when it is hot and dry – During hot and dry conditions, trees will actually “shut down” and no water will be used by the tree. Unreasonable amounts of irrigation would therefore lead to wet soils and subsequently a reduced amount of oxygen in the soil which will undoubtably lead to stress. Furthermore, irrigating long cycles and applying large volumes of water during flowering will invariably lead to increased nutrient leaching, which will lead to reduced nutrient availability and reduced tree performance.

In summary, macadamia growers are advised to frequently irrigate trees during the flowering period and use irrigation scheduling tools to carefully monitor soil moisture content. Growers are also advised to invest in mulching material if water is limited, as the addition of the mulch will reduce soil evaporation and make the little bit of water that you have last a bit longer.

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