Updated: Jul 13, 2021
Hull split is around the corner in California and the northern hemisphere and growers need to apply strategic deficit irrigation, to achieve better uniformity of hull-split through each tree. An optimized hull-split process can also reduce the impact of navel orangeworm (NOW) d the costly spray programs required to manage it.
Our hull-split algorithm is here to help growers do just that.
AlmondBeat #5, here we go.
Preparation starts in Spring
Uniformity of hull split throughout each field/block improves quality and brings many operational benefits; less re-shaking and better utilization of harvest and processing assets. A primary reason for poor uniformity at the block level is poor irrigation decisions during the season that lead to excess water movement to low-lying areas. Phytech provides confidence throughout the season to reduce the irrigation, either volume or duration, whenever possible so there is less drainage to the lower parts of blocks where delayed hull split becomes an issue. The benefits of this are available in the first season but most growers report a continual improvement over subsequent seasons. So, irrigation decisions during spring and early summer affect hull split uniformity across a block, but as every almond grower knows, uniform hull split throughout a tree is rare to see. But could it be better?
Less is more - the benefits of deficit irrigation
Inducing mild to moderate daily stress patterns on the almond tree during late June and July, dependent on season, maturity level and variety, is the best way to improve hull-split uniformity, help with crop removal and facilitate a slightly earlier harvest. The longer those open nuts hang on the trees - the longer they're susceptible to damage and hull-rot. Another benefit is that drier fields are more easily accessible by large harvesting machinery.
Walking a tightrope
By reducing water delivery and applying stress the tree needs to draw water from the hull. When water leaves the hull, back through the tree, the split occurs. Now comes the hard part: how to control this deficit strategy?
Apply too much stress, or cumulative stress over multiple days, and the uniformity of the hull split throughout the tree will be poor. The hulls at the top and outer edges of the tree will open further and sooner than the hulls lower in the tree and further inside the canopy.
Apply too little stress and the hull split will be delayed, leading to higher risk of pest and disease. Too little stress is normally associated with higher soil moisture levels and higher canopy humidity, which leads to increased hull rot pressure and reducing the capacity to dry almonds once on the ground.
So an effective deficit-irrigation plan is challenging and requires a delicate balance. Over-irrigating, apart from wasting precious water resources, might increase NOW pressure, hull rot, barking and the ground drying time, while too much stress can affect kernel weight and next year's yield, reduce the percentage of nuts coming off in the first shake and increase the chance of mummy nuts.
Letting the trees tell you
Relying on weather, soil moisture data or other indirect methods is not enough. As usual, it's better to ask the trees. First, Phytech helps you identify the beginning of hull split. Check the Dashboard stress maps on a weekly view and see which of your blocks experience higher numbers of stress days through June – these are the blocks where hull split will occur first.
Then, by listening to the trees and using Phytech's hull-split algorithm, growers can fine tune the irrigation to optimize hull split. Creating a mild-to-moderate consistent daily stress over several weeks, doesn't trigger a "panic" water-drawing by the tree, but rather leads to a gentle and persistent pull of water from the hulls by the tree. A continuous hull split, rather than stop-start, reduces the opportunity for NOW or hull rot to take hold. The uniformity of hull split throughout the tree is also much better, enabling more nuts to be removed in the first shake.
No need to guess what the trees are experiencing. Delivering water and immediately getting real-time feedback from the trees help growers adapt their irrigation and control the hull-split process.
Here's a snap shot of a 2 weeks period, showing the constant feedback between the irrigation timing and quantity and the trees' response:
Below is an almond block as seen on Phytech's web interface before, during and after the hull-split period.
It's a good example of how growers are switching to a high frequency/lower quantities plan, while getting constant, direct feedback from the trees (growth rate and water-demand) to support their deficit irrigation strategy.
That's it for now. Keep on learning and stay tuned for our next AlmondBeat report.