Walnuts: When to Start IrrigatingKen Shackel

Sac-Solano-Yolo Walnut DayFeb 23rd, 2016

Objective #1: Field test four levels of SWP for the start of irrigation in the spring.

Walnut board funded project:Early season water management and physiological

indicators for irrigation management in walnutPIs: Ken Shackel, Allan Fulton, Bruce LampinenGraduate students & postdocs: Nick Matsumoto, Valentin Couvreur, Daniela Jerszurki

Year 2…

In the spring, use a pressure chamber, measure SWP

1) Let the grower do what he wants.2) For us, wait to start irrigating, until the

trees hit:1, 2, 3, or 4 bars below (more stressed than) the ‘baseline’ (fully irrigated) SWP value.

50

40

30

20

10

0APR MAY JUN JUL AUG SEP OCT NOV

Date, 2015

(ETc )

Grower

Cum

ulat

ive

appl

ied

or c

alcu

late

d w

ater

(inc

hes)

(Grower)

Orchard demand (ETc) and applied irrigation

50

40

30

20

10

0APR MAY JUN JUL AUG SEP OCT NOV

Date, 2015

(ETc )

Grower

1 bar

Cum

ulat

ive

appl

ied

or c

alcu

late

d w

ater

(inc

hes)

(1 bar)(Grower)

Orchard demand (ETc) and applied irrigation

50

40

30

20

10

0APR MAY JUN JUL AUG SEP OCT NOV

Date, 2015

(ETc )

Grower

1 bar

2 bar

Cum

ulat

ive

appl

ied

or c

alcu

late

d w

ater

(inc

hes)

(2 bar)(1 bar)

(Grower)

Orchard demand (ETc) and applied irrigation

50

40

30

20

10

0APR MAY JUN JUL AUG SEP OCT NOV

Date, 2015

(ETc )

Grower

1 bar

2 bar3bar

Cum

ulat

ive

appl

ied

or c

alcu

late

d w

ater

(inc

hes)

(3 bar)(2 bar)

(1 bar)(Grower)

Orchard demand (ETc) and applied irrigation

50

40

30

20

10

0APR MAY JUN JUL AUG SEP OCT NOV

Date, 2015

(ETc )

Grower

1 bar

2 bar4 bar

3bar

Cum

ulat

ive

appl

ied

or c

alcu

late

d w

ater

(inc

hes)

(4 bar)(3 bar)

(2 bar)(1 bar)

(Grower)

Orchard demand (ETc) and applied irrigationResult: about 1 month delay, then pretty rapid drop in SWP.

2

0

-2

-6

-8APR MAY JUN JUL AUG SEP OCT

Date, 2015

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

**** ************** * ** * ** * ** *

-4

SW

P –

Bas

elin

e (B

ar)

Midday SWP (difference from baseline)Result: once normal irrigation was restored, not much

difference in SWP.

15

APR MAY JUN JUL AUG SEP OCT

Date, 2015

Soi

l wat

er c

onte

nt (i

nch)

to 6

’

10

5

0

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

FEB MAR

Soil moisture to 6’Result: Grower (most applied water) ended the season with

the driest soil, but not sure if this is a ‘real’ effect.

2014 Plot Yield(lbs/ac)

Tree sample nut weight (g) Plot PAR Plot Yield/PAR

Treatment Lbs/ac (% Grower) Weight (% Grower) PAR (% Grower) Y/P (% Grower)

1 bars below 3700 100 10.3a 98 86 102 43.0 98

Grower 3690 100 10.4a 100 84 100 43.8 100

2 bars below 3440 93 10.1ab 97 88 104 39.3 90

3 bars below 3420 93 9.4bc 91 85 101 40.0 91

4 bars below 3360 91 9.1c 87 88 104 38.4 88

Treatment yield data

2015 Plot Yield(lbs/ac)

Tree sample nut weight (g) Plot PAR Plot Yield/PAR

Treatment Lbs/ac (% Grower) Weight (% Grower) PAR (% Grower) Y/P (% Grower)

Grower 5170a 100 9.42a 100 89.3 100 58.0a 100

1 bars below 4970ab 96 9.18ab 97 88.8 99 56.0ab 97

2 bars below 4510ab 87 9.22ab 98 90.8 102 49.6ab 85

3 bars below 4350ab 84 8.89b 94 89.1 100 48.9ab 84

4 bars below 4170b 81 8.44c 90 89.9 100 46.4b 80

2014 Plot Yield(lbs/ac)

Tree sample nut weight (g) Plot PAR Plot Yield/PAR

Treatment Lbs/ac (% Grower) Weight (% Grower) PAR (% Grower) Y/P (% Grower)

1 bars below 3700 100 10.3a 98 86 102 43.0 98

Grower 3690 100 10.4a 100 84 100 43.8 100

2 bars below 3440 93 10.1ab 97 88 104 39.3 90

3 bars below 3420 93 9.4bc 91 85 101 40.0 91

4 bars below 3360 91 9.1c 87 88 104 38.4 88

Treatment yield data

Treatment Nut weight (g)

LgJm(%)

LgSd(%)

Shrivel(%)

Mold(%)

OffGr.(%)

Ex. Lt.(%) RLI Relative

Value

Grower 10.4a 78.7a 78.9a 2.8 1.6 2.3 60 53.5 0.88

1 bars below 10.3a 76.9ab 77.8a 2.6 2.1 2.8 63 54.2 0.89

2 bars below 10.1ab 75.1ab 76.0a 1.7 2.2 2.5 59 54.1 0.90

3 bars below 9.4bc 61.1bc 62.9ab 2 1.3 1.9 56 53.1 0.88

4 bars below 9.1c 49.2c 52.0b 2.6 1.6 2.2 61 53.8 0.89

Treatment Nut weight (g)

LgJm(%)

LgSd(%)

Shrivel(%)

Mold(%)

OffGr.(%)

Ex. Lt.(%) RLI Relative

Value

Grower 9.4a 63a 68a 2.4 0.9 1.6 47 54.8 0.92

1 bars below 9.2ab 59a 63a 2.3 0.8 1.3 52 55.2 0.91

2 bars below 9.2ab 59a 65a 2.1 1.1 1.6 43 55.1 0.91

3 bars below 8.9b 54ab 58ab 2.6 1.3 2.0 40 54.9 0.93

4 bars below 8.4c 44b 48b 2.5 1.5 2.2 43 54.5 0.93

2014

2015

Treatment nut quality data

Nut

wei

ght (

g)

10

9

8

7

SWP – Baseline (Bar)-2 -1 0-3-4-5 1

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

Nut weight: clear relation to SWP in JuneBoth across as well as within treatments

Conclusions thus far for yield, nut weight, nut size and quality:• Trend for decreasing yield and nut weight & size (but not nut

quality) with longer delays in irrigation.• Overall effects are still relatively small (3-4%) for a 1 bar

threshold, which gives about a 1 month delay.• Nut weight effects appear to be closely related to June SWP,

suggesting that a strategy of irrigation delay followed by sufficient irrigation to reach baseline SWP in June may be advantageous. (Plant-based irrigation scheduling).

Implications for irrigation scheduling in general:“Stress is as stress does”(F.Gump, 1994)

ET-based scheduling:Nut weoght could be

related to how far ‘behind’ each treatment

was from ETc in June

OR

Soil-based scheduling:Nut weight could be

related to how dry the soil was in each

treatment in June

Nut

wei

ght (

g)

10

9

8

7

SWP – Baseline (Bar)-2 -1 0-3-4-5 1

Nut weight & SWP in June (individual trees)r2 = 0.67***

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

Nut

wei

ght (

g)

10

9

8

7

SWP – Baseline (Bar)-2 -1 0-3-4-5 1

Nut weight & SWP in June (plot means for blocks 2 and 4)r2 = 0.65**

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

Nut weight & ET-based deficit in Juner2 = 0.07

Nut

wei

ght (

g)

10

9

8

7

Inches of water above (+) or below (-) ET target, including soil contribution-4 0-12 4

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

-8-16

Nut weight & Soil-based deficit in Juner2 = 0.00

Nut

wei

ght (

g)

10

9

8

7

Soil moisture content to 6’ (inches)4

Grower1 bar2 bar3 bar4 bar

Symbol Treatment

6 8 10 12 14 16 18

Neither ET- nor soil- approaches appear to account for the observed nut weight effects in this study.

Trees must get their water from somewhere. Does combining soil information with ET information help to interpret how the trees are responding?

Estimates of an overall orchard water balance were made.

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Symbol Source

Grower Practice (ETc)

Orchard water balance estimates

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Rain

Symbol Source

Grower Practice (ETc)

Orchard water balance estimates

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Rain

Symbol SourceSoil

Grower Practice (ETc)

Orchard water balance estimates

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Rain

Symbol SourceSoil

1 Bar below (ETc)

Orchard water balance estimates

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Rain

Symbol SourceSoil

(ETc)2 Bar below

Orchard water balance estimates

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Rain

Symbol SourceSoil

(ETc)3 Bar below

Orchard water balance estimates

APR MAY JUN JUL AUG SEP OCT

Date, 2015

40

Cum

ulat

ive

inch

es o

f wat

er 30

20

10

0

Irrigation

Rain

Symbol SourceSoil

(ETc)4 Bar below

Orchard water balance estimates

15

APR MAY JUN JUL AUG SEP OCT

Date, 2015

Soi

l wat

er c

onte

nt (i

nch)

to 6

’

10

5

0FEB MAR

(Soil moisture to 6’)Over half of the total seasonal soil water usage

occurred in May, during the period with no irrigation

(May 1)

(May 31)

(Oct 31)

8”

1.5’

2.5’

3.5’

4.5’

5.5’

Dep

th

0-0.2 +.2 0-0.2 +.2 0-0.2 +.2 0-0.2 +.2 0-0.2 +.2

Average change in water content (inches/foot)

Grower 1 bar 2 bar 3 bar 4 bar

Pattern of water depletion with soil depth in May:Peak activity at shallow depths in Grower compared to other treatments.

Pattern of deeper root activity could indicate

improved root health with delayed start of irrigation.

Interesting (and unexpected) increase in early season total water use by 4 bar treatment. May again suggest an

advantage of a delayed start followed by SWP recovery to baseline.

Recap: When to Start Irrigating.• 1 bar threshold appears to be a reasonable indicator for the start of

irrigation, and lower thresholds are not associated with decreased nut quality.

• June may be an key month to maintain SWP near baseline values (a ‘plant-based’ irrigation scheduling approach).

• Some indication of a change in early season root and ET activity, but so far no obvious improvement in tree health or productivity with a delayed irrigation start.

Thanks for your attention, and thanks to funding from the

California Walnut board.

Questions?

ET Irrigation Scheduling Emails

Kat PopeOrchard Advisor

Sacramento, Solano & Yolo Countieskspope@ucanr.edu

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