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May Irrigation Stress In Almonds

Mitigating kernel stress during kernel expansion is one of the top priorities for every almond farmer in the state, but as we venture into May this priority can shift to crop protection and field sanitation. Balancing tractor work to apply pesticides with irrigations is more challenging during the month of May due to the increase in crop water demand and strings of hot and windy days that delay sprays.

Effects of Stress during Nut Fill

A question often asked by customers is how bad it is for a field to be outside of the optimum blue band soil moisture range. The answer to this question depends upon how far and how long a field is outside of the range. For example, small variations for short amounts of time tend to cause minimal stress in plants and result in little to no loss in kernel size during solidification. In contrast, large variations for extended periods of time tend to cause high stress in plants and warrant greater concern regarding irreversible loss in final crop weight and quality by harvest.

To exemplify the effects, below I compare two double line drip fields that received similar water allocations but had significantly different levels of water availability during the month of May.

52% Compliance

The first field scored 52% within the ideal range for transpiration and had a soil moisture deficit down to 3 feet following the May Spray. Although water was applied to this field for a total of 98 hours and 22 minutes, it did not recover the 36” soil horizon and slowly lost moisture at 24” and 12” soil horizons. The depletion in water availability reduced root activity and minimized the mass flow of water and nutrition available to the trees.

A screenshot of a map Description automatically generated

90% Compliance

The second field scored 90% within the ideal range for transpiration and did not have a soil moisture deficit following the May Spray.  Water was applied for a total of 89 hours and 58 minutes in this field. Between May 13th and May 18th some lateral water movement was lost at the 24” soil horizon, but it was recovered on the May 18th irrigation. Throughout the month of May the graph shows strong root pull throughout the entire root zone with little to no downtime in water and nutritional uptake.

A close up of a map Description automatically generated

How Does it Affect Yield & Quality?

On May 20th almond kernels were analyzed from both fields. The 90% compliant field maintained the kernel size established in April to the 80% kernel solidification mark with no kernel shrivel and with high turgor pressure within the remaining 20% of the jelly. The 52% compliant field showed the effects of April’s cell expansion with kernel shrivel, dimpling within the jelly region and a reduced weight. By analyzing crop water availability with soil tension, we can properly quantify stress during nut fill.

For any questions on irrigation management regarding almonds please contact your local Hortau representative.

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