Harvest is approaching fast in California and the northern hemisphere and in many areas across the Central Valley (depending on variety, weather and trees' stress conditions) it's hull-split time.
Let's go over some basic irrigation principals based on real-time data from the trees, to help you optimize in this critical phase of the season.
22 AlmondBeat #4, here we grow.
The benefits of optimized hull-split
There are two risks that might cause hull rot and usually are dealt by spraying the orchards:
Navel orangeworm (NOW) females can detect the released chemicals and lay their eggs in the nut
The nut is more susceptible to fungi infections (Rhizopus Stolonifer and Aspergillus niger)
On the positive side of things, 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.
The most effective way to optimize hull split is by switching to Regulated Deficit Irrigation (RDI)
Less is more
Inducing mild to moderate daily stress patterns on the almond tree during late June and July, depending 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. As mentioned, The longer those open nuts hang on the trees - the longer they're susceptible and hull-rot. Another benefit is that drier fields are more easily accessible by large harvesting machinery.
The balancing art of RDI
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 reduce irrigation without inducing yield-affecting stress?
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.
An effective RDI plan requires walking a tightrope. Over-irrigating (apart from wasting precious water resources), might increase 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. Growers are looking to keep their trees' growth minimal, while being in the yellow-to-orange status and avoiding a series of consecutive red-stress days.
Letting the trees guide us
First, growers can detect the beginning of hull-split by following the trees' signals in each block. see which of your blocks experience higher numbers of stress days through - these are the blocks where hull split will occur first.
Next, 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 a "stop-start", reduces the danger for 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.
But RDI shouldn't be an automated response, once hull-split starts.
It all depends on what trees are telling you. In this example below, trees were already experiencing stress periodically, so no need to cut more water that might danger future productivity and health.
And here below is an opposite example, where trees' growth rate is high, and the grower should definitely need to consider reducing irrigation:
Here's a snapshot 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 listening to your trees and stay tuned for our next AlmondBeat report.