Almond's Water Use Efficiency
Over the past few decades, there have been several efforts to develop a water production function (WPF) for almond. A WPF is simply the amount of crop produced per an applied amount of water. These projects typically work within established commercial orchards, and researchers monitor the amount of water being applied while measuring yield components at harvest. WPF projects have occurred in all major almond producing areas.
One Interesting aspect of WPF experiments is determining the value of water. Nearly every crop has a positive yield response to increasing water applications. This response tends to be non-linear or polynomial, meaning that the response changes with differing amounts of water application. As the amount of water applied (either by irrigation or rainfall) begins to approach full crop evapotranspirational demand (ETc), the yield response from the additional water tends to decrease. If water applications exceed ETc, yields will no longer increase and, in the cases of severe over-irrigation, may decrease due to root disease and other tree health issues.
A common observation of multiple almond WPF is the near-linear yield response to increased water applications when the trees are receiving less than full irrigation (Figure 1, A). This aspect is typically observed at the lower irrigation levels and tends to continue to around 85-90% of ETc. After this point, the slope changes, and the tree is less efficient with more water applied (Figure 1, B). If water applications exceed ETc, yields do not increase and may decline (Figure 1, C). This suggests that applying 85-90% of ETc will maximize the water use efficiency. Furthermore, these studies show that maximum water use by the almond tree does not provide the maximum water use efficiency. Therefore applying water to achieve maximum yields (between 90%-100% of ETc) should only occur when the expenses of applying that water are minimized.
The yield response to increased water applications from various experiments has varied. Work published in 2017 from a ‘Nonpareil’ and ‘Monterey’ orchard in Kern County found that every additional acre inch applied up to 90% of ETc increased yield by roughly 70 kernel lbs of yield. This amount was significantly more than what was identified in a multi-location study conducted within ‘Nonpareil’ blocks in Kern, Merced, and Tehama Counties between the years of 2011-2017. This study identified a 50 lb increase for every additional acre inch of water applied. Lastly, and more recently, a 2020 study out of Spain working with ‘Guara’ identified a 96 kernel lb increase for every acre inch applied. It should be noted that this last study was within a region that receives considerably more rainfall which offsets much of the irrigation requirement.
The cause of the observed variability between the studies is not really known. It does appear that areas receiving less rainfall have a greater yield response to water applied. Orchard conditions, including age of the trees and irrigation systems, were different across all locations. Rootstocks are also differed, in which peach x almond hybrid rootstocks did appear to be more responsive to water applications. Lastly, the yield produced varied from year-to-year, tied to both the effects of the water deficits and the normal alternative bearing patterns of the tree.
Even with the variability, the data provided from these studies are useful. If we average the yield response from the five trial locations, we find that an average of 61 kernel pounds was produced for every acre inch of water applied up to 85/90% of full ETc (0.27 kg kernel/m3 of applied water). This value can be utilized within an operation to determine the value of that water, once accounting for operational expenses (~$1/kernel pound, based on UC Davis Cost Studies), and the value of a kernel pound. As highlighted in the sensitivity table (table 1), the value of water is strongly dependent on the sales price of almond kernels. For example, an acre inch of water has approximately $31 in value when almond prices are a $1.50/lb, but a value of $152 when prices are $3.50/lb. Please note that water applications less than 85% of ETc will reduce yield, therefore increasing the operational expenses per lb of kernel produced.
Value per lb of kernel
$1.50
$2.00
$2.50
$3.00
$3.50
Value of crop produced (61 lbs of kernel/acre inch applied)
$91.50
$122.00
$152.50
$183.00
$213.50
OPEX, excluding water costs for 61 lbs ($2500/acre for 2500 lbs/acre)
$61.00
$61.00
$61.00
$61.00
$61.00
Break even point for 1" of applied water
$31.50
$61.00
$91.50
$122.00
$152.50
These studies provide an understanding on how almond yields respond to increased water applications. They highlight the value of irrigating to a maximum water use efficiency rather than maximum water demand. Furthermore, the consistency in the results have indicated that the highest water use efficiency will occur when trees are irrigated at 85-90% ETc, providing the greatest financial value from the water applied. Lastly, when managing drought and water shortages, it can provide an understanding on how much can be paid for water without occurring an operational loss.
For more information on managing almonds during a drought, please review these articles:
Almond Drought Management: 2021 Update
Drought Management for California Almonds
Works referenced:
Haviland, et al. 2019. Sample Costs to Establish an Orchard and Produce Almonds.
Goldhamer, D. and E. Fereres. 2017. Establishing an almond water production function for California using long-term yield response to variable irrigation. Irrig. Sci. 35:169-179. https://doi.org/10.1007/s00271-016-0528-2
Moldero, et al. 2021. Long-term almond yield response to deficit irrigation. Irrig. Sc. https://doi.org/10.1007/s00271-021-00720-8