In the San Joaquin Valley, we have approached the point that growers and their irrigation managers are planning deficit irrigation strategies around hull split. If you have not thought this through, it would be very beneficial to spend some time to plan your irrigation before it is a crisis.
This water use is driven by the process of gas exchange of carbon dioxide and transpiration which is required for photosynthesis. Environmental conditions (hot and dry will use more than cool and humid), the percent of the ground covered by the plant (higher percent, more water use, but more yield), and the stage of the plant (large leaves use more than little leaves) impact the amount of water required per acre/plant.
In years where less water is available, deficit irrigation can be used with little negative effect on yield if it’s carefully monitored. A well-planned plant-driven nutrition plan and managing plant stress during peak heat/drought stress is essential. Since a drought situation is not “business as usual,” there is a need for a carefully planned strategy on how best to utilize the water that is available. This practice, however, can have negative impacts when applied incorrectly. During deficit irrigation, irrigation can be reduced until soil moisture levels deplete below 50%.
For almonds, this strategy is most commonly used around hull split.
General guidelines on the timing and duration of almond deficit irrigation:
1. When a “V” begins to form on the hull just prior to the start of hull split, irrigations should begin to decrease. During this time, if your soil moisture levels are already depleted, it’s important not to induce any more stress than what is already there.
2. The period of deficit irrigation should last no longer than two weeks to prevent any long-term damage. Inducing too much stress for too long is detrimental to your crop as this final phase in development is occurring in preparation for harvest. When your two weeks of deficit irrigation are finished, resume your irrigation schedule and begin to fill the soil profile again just before harvest.
For pistachios, deficit irrigation is best used during shell hardening (phase 2) and post-harvest.
General guidelines on the timing and duration of pistachio deficit irrigation:
1. For pistachios the critical periods when you cannot under-irrigate are from bloom to shell expansion (stage 1) and nut filling to hull slip (phase 3).
2. Studies have shown that the best production occurred with deficit irrigation during Stage 2 at 50% of near-potential ETc during Stage 2 and 25% of near-potential ETc after harvest.
If possible, schedule your irrigation during early morning or late evening (between 7pm and 7am) to avoid evaporation losses. Temperatures are higher during the day, and this can lead to excessive water losses, thus reducing the overall efficiency of the irrigation system. However, scheduling irrigation during early morning or late evening may not be practicable for some production systems due to crop type, system design, and logistics of operation.
California’s climate is normally hot and dry during the summer months, but drought conditions and higher-than-average temperatures make farming even more challenging. The establishment of these strategies can be used to ensure that your farm remains productive during drought.
We know these are some general guidelines and everyone has a different set of problems. Please feel free to call me or your Ultra Gro Crop Advisor for more details, or, with any help I can lend to your specific situation. I can be reached at my cell phone: 559-907-8405.