Plant-Based Measures of Water Stress for Irrigation Management in Multiple Almond Varieties

Objectives: 1). Determine if there are differences in water-stress responses among almond varieties as measured by stem water potential (SWP).

2). Determine if the differences are related to inherent physiological differences among the varieties.

Project Leaders: Ken Shackel (UC Davis Plant Sciences) and David Doll (UCCE Merced County)

Background: Accurate and timely irrigation management is a key to both successful almond production and appropriate environmental stewardship, especially in times of protracted water shortages. In recent years, in deciding when and how best to irrigate, growers have relied increasingly on gauging the trees’ level of water stress by using a pressure chamber—“the Bomb”—to measure SWP. The researchers plan to build on the baseline (non-stressed) SWP values that have been developed for Nonpareil (NP), and whether they carry the same implications as those in NP.

Results:1. Differences in stem water potential were found at two locations.2. At the Livingston Trial, Fritz was 1.2 bars more stressed than NP. At Kearney Ag Center,

Carmel was 0.48 bars less stressed than NP. 3. Even during periods of high stress, the varieties responded similarly.4. Timing the irrigation to when the trees were -2 to -3 bars below baseline appeared to

match the calculated ET demand.5. Plant stress that occurred t due to early season irrigation deficits was reduced with

additional water applications in the later season.

Conclusions:1. With the exception of harvest, Carmel and Butte in mature orchards do not need to be managed differently. 2. Fritz appears to require more water than NP, while in young orchards, Carmel appears to need less water

than NP. 3. The greatest difference between Fritz and NP occurred during the dry-down for NP harvest. Separate

irrigation systems may be of benefit to help alleviate stress during this time.4. Differences may be due to either physical characteristics such as tree size, number of leaves per tree, or size

of the root zone, or plant-water use efficiency differences which include crop-load tree response, or stomatal conductance rates.

Orchard Variety Number of Trees

Times Measured

Mean SWP(bars)

Livingston Nonpareil 12 20 -9.77

Fritz 12 20 -10.95*

Kearney Nonpareil 24 21 -11.17

Ag Center Butte 24 21 -11.11

Carmel 24 21 -10.69*

Le Grand Nonpareil 12 16 -13.60

Carmel 12 16 -13.79

Monterey 12 16 -14.07

Merced Nonpareil 22 24 -11.17

Carmel 14 24 -11.22 Acknowledgements: Thanks to Robert Chad, Sperling Orchards, and Ted Walsh for the use of their orchard in this study. Thanks to Daniel Brooks for countless hours of pressure bombing this past summer.

Figure 5: Applied water to the orchard located near Merced (black line) shown in comparison to a calculated fully irrigated almond orchard with and without a cover crop (dotted blue and solid blue lines, respectively). Orchard was full canopy, cover-cropped with row strips, spaced 20’x20.’

Figure 6: Applied water to the orchard located at Kearney Ag Station (black line) shown in comparison to a calculated fully irrigated almond orchard with and without a cover crop (dotted blue and solid blue lines, respectively). Orchard was 40% filled canopy, cover-cropped with row strips, spaced 22’x17.’

Figure 7: Applied water to the orchard located near Livingston (black line) shown in comparison to a calculated fully irrigated almond orchard with and without a cover crop (dotted blue and solid blue lines, respectively). Orchard was full canopy, cover-cropped with row strips, spaced 22’x18.’

Figure 8: Applied water to the orchard located near Le Grand (black line) shown in comparison to a calculated fully irrigated almond orchard with and without a cover crop (dotted blue and solid blue lines, respectively). Orchard was full canopy, cover-cropped with row strips, spaced 22’x18.’

Figure 1: Weekly stem water potential values from a full canopied orchard of Nonpareil and Carmel in comparison to a calculated baseline using CIMIS. The orchard is located near Merced, CA. Spacing: 20’x20.’

Figure 2: Weekly stem water potential values from a 2nd leaf, 40% filled canopy orchard of Nonpareil, Butte, and Carmel in comparison to a calculated baseline using CIMIS. The orchard is located at Kearney Ag Station near Reedley, CA. Spacing: 22’x17’

Figure 3: Weekly stem water potential values from a closed canopy orchard of Nonpareil and Fritz in comparison to a calculated baseline using CIMIS. The orchard is located near Livingston, CA. Spacing: 22’x18’

Figure 4: Weekly stem water potential values from an 80% filled canopy orchard of Carmel, Monterey, and Nonpareil in comparison to a calculated baseline using CIMIS. The orchard is located near Le Grand, CA. Spacing: 22’x18’

Table 1: Mean stem water potentials measured from four different orchards comparing varieties over the 2010 growing season. * indicates significant difference between the indicated variety and Nonpareil,P< 0.05