Irrigation Management for California Walnut Production

Richard Buchner, Allan Fulton, Bruce Lampinen and Ken Shackel

Potential ET = 42 acre – inches

Little or no effective rainfall

Nearly all California walnut acreage is irrigated

Soil Moisture Monitoring

Difficulties areDifficulties are……

♦Measurement locations and depths are representative

♦Correctly defining management thresholds♦Accurate equipment calibration

Water Balance or Budget Approach

Difficulties areDifficulties are……

♦Reliable estimate of evapotranspiration♦Reliable estimate of stored soil moisture♦Reliable estimate of applied water♦Does not account for site specific conditions♦Less useful for managing moisture stress

Why An Interest in SWP?

Where does a tree get its water and is all crop stress

bad?

How well does regional weather and general estimates of crop ET fit specific orchard conditions? Is

SWP an improvement?

What is SWP Indicating?

Soil Water Potential -1/3 to -2 bars Suction

Tree Water Potential -2 to -35 bars Suction

Atmospheric Water Potential -50 to -60 bars Suction

14.5 psi per bar suction

How is SWP Measured, Conceptually?

Preferred leaf sampling position

Alternate position(s)

Plant based irrigation scheduling

Air Pressure

(PressureGauge)

Magnifying Glass

Water Coming Out(Artists conception)

(Plastic bag)

(Seal)

C

B

D

A

How is SWP Measured in the Field?

Black Butte Walnut Irrigation Trial

Black Butte Walnut Irrigation Trial, 2003

treatment CIMIS Low Stress Mild Stress Mod StressTarg1 Targ2 Targ3

bars

-15

-10

-5

0

Date

01MAY03 01JUN03 01JUL03 01AUG03 01SEP03 01OCT03

2003Black Butte Walnut Irrigation Trial, 2002

treatment CIMIS Low Stress Mild Stress Mod StressTarg1 Targ2 Targ3

bars

-15

-10

-5

0

Date

01MAY02 01JUN02 01JUL02 01AUG02 01SEP02 01OCT02

2002

Shoot Growth

Cumulative grow th (centimeters) of pruned Chandler w alnut shoots grow n on Paradox Rootstock in low , mild, and moderate stressed irrigation treatments. Average +/- standard error.

0.0100.0200.0300.0400.0500.0600.0700.0800.0900.0

1000.01100.01200.01300.01400.0

4/15

/200

3

4/22

/200

3

4/29

/200

3

5/6/

2003

5/13

/200

3

5/20

/200

3

5/27

/200

3

6/3/

2003

6/10

/200

3

6/17

/200

3

6/24

/200

3

7/1/

2003

7/8/

2003

7/15

/200

3

7/22

/200

3

7/29

/200

3

8/5/

2003

8/12

/200

3

DateC

umul

ativ

e Sh

oot G

row

th (c

entim

eter

s)Low Stress, Mild Stress Moderate Stress

Cumulative grow th (centimeters) of pruned Chandler w alnut shoots grow n on Paradox Rootstock in low , mild, and moderate stressed irrigation treatments. Average +/- standard error.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

110.0

120.0

5/6/02

5/13/0

25/2

0/02

5/27/0

26/3

/026/1

0/02

6/17/0

26/2

4/02

7/1/02

7/8/02

7/15/0

27/2

2/027/2

9/02

8/5/02

8/12/0

28/1

9/02

Date

Cum

ulat

ive

Shoo

t Gro

wth

(cen

timet

ers)

Low Stress, Mild Stress Moderate Stress

y = 1185.2e0.9525x

R2 = 0.42

051015202530354045

-9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0

Midday stem w ater potential (SWP) - bars

Aver

age

mon

thly

gro

wth

of p

rune

d sh

oots

(cm

)

Correlation between shoot growth of pruned Chandler trees on Paradox rootstock and midday stem water potential

Nut Growth

Cumulative nut sizing of Chandler walnut on Black Walnut Rootstock grown under low, mild, and moderate levels of tree stress. Tehama

County 2003.

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

6/11/03

6/18/03

6/25/03

7/2/03

7/9/03

7/16/03

7/23/03

7/30/03

8/6/03

8/13/03

DateW

alnu

t Dia

met

er (m

m)

Low Stress Mild Stress Moderate Stress

Cumulative nut sizing of Chandler walnut on Paradox Rootstock grown under low, mild, and moderate levels of tree stress. Tehama County,

2002.

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

May 6 - 16 May 16 - 30 May 30-Jun 8 June 8-19 June 19-28 Jn 28 - Jul10

Date

Wal

nut D

iam

eter

(mm

)

Low Stress Mild Stress Moderate Stress

Tehama Quality and Yield

Treatment%

large % mold % insect % shrivel

% adhering

hull RLI

Dry Wt. Yield

(tons/ac)

Low 96.0 a 0.83 b 0.0 a 1.04 b 1.25 a 51.5 a 1.98 a

Mid 94.5 a 2.62 a 0.12 a 2.29 a 0.83 ab 51.3 a 1.84 a

Moderate 85.7 b 2.29 a 0.17 a 2.71 a 0.42 b 52.2 a 1.74 a

LSD 3.0 0.84 0.17 0.93 0.67 1.6 0.35

2002 Nut Quality and Yield for Stress Treatments

Reasons to Manage Stress in WalnutReasons to Manage Stress in Walnut

♦Sunburn/Shrivel♦Growth/Yield♦Frost Injury♦Tree Training♦Nut Size♦Pest Resistance

♦Kernel Fill♦Kernel Color♦Black Husk/Mold♦Oil-less Nuts♦Codling Moth/ Husk Fly♦Mites

Interpreting SWP Measurements in Walnuts

0 to –2.0 Not commonly observed

-2.0 to –4.0Fully irrigated, low stress, commonly observed when orchards are irrigated according to estimates of real-time evapotranspiration (ETc), long term root

and tree health may be a concern

-4.0 to –6.0 Low to mild stress, high rate of shoot growth visible, suggested level from leaf-out until mid June when nut sizing is completed

-6.0 to –8.0

Mild to moderate stress, shoot growth in non-bearing and bearing trees has been observed to decline especially with Black Walnut Rootstock. These levels do not appear to affect kernel development and may be appropriate

during kernel development

-8.0 to –10.0 Moderate to high stress, shoot growth in non-bearing trees may stop, nut sizing may be reduced in bearing trees

-10.0 to –12.0High stress, temporary wilting of leaves has been observed. New shoot

growth may be sparse or absent and some defoliation may be evident. Nut size likely to be reduced.

-12.0 to –14.0 Relative high levels of stress, moderate to severe defoliation, should be avoided

-14.0 to –18.0 Severe defoliation, trees are likely dying

SWP Reading (- bars)