Scheduling irrigations for apple trees using climate data
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Transcript of Scheduling irrigations for apple trees using climate data
Scheduling irrigations for apple trees using climate data
Ted Sammis
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The Water Budget Method
• The tree root zone is a reservoir
• Water is added by irrigation or rainfall.
• Water is removed by evapotranspiration.
• Added water can be lost by deep percolation if the amount exceeds the field capacity of the soil.
Management Allowed Depletion
• Management Allowed Depletion Is the percent of water that can be removed before soil moisture stress limits growth.
• (For Apples MAD is %50.)
Evapotranspiration
• Evapotranspiration is determined from climate data to calculate potential Evapotranspiration (water used by grass) and a scaling coefficient or crop coefficient for apples.
• The crop coefficient depends on the size and spacing of the trees and the ground cover.
• The crop coefficient changes throughout the growing season increasing to a maximum at maximum leaf cover
Potential Evapotranspiration
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
11/1/1998 2/9/1999 5/20/1999 8/28/1999 12/6/1999 3/15/2000
Date
Eto
in
ch
/da
y
Crop coefficient scaling function for trees based on projected area
y = 1.1728x0.5845
R2 = 0.9957
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1
Shaded area/tree spacing
Cro
p C
oe
ffic
ien
t S
ca
lin
g f
acto
r
Calculation of Evapotranspiration
• Potential Et= 0.3 inches / day
• Et= K*PET
• K= 0.8
• Et= 0.8* 0.3 = .24 inch/day
Daily Apple Evapotranspiration
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0 50 100 150 200
Days since bud break
Eva
po
tra
ns
pir
ati
on
(in
ch
es
/da
y)
Calculated when to irrigate
• Readily available water (RAW) = available water (AW) * management allowed depletion (MAD)
• Example:
• Aw = 2 inches/ft * 3ft root zone
• Mad = 50%
• RAW= 2 inches/ft*3ft*0.5 = 3 inches
Irrigation Interval
• Irrigation interval = RAW / Et / day
• Irrigation interval = 3 inches / 0.24 inches /day = 13 days
• Irrigation interval changes with changes in the Et or soil type.
• Et changes with tree cover and weather.
Source of Potential Evapotranspiration
• New Mexico Climate Center Homepage
• http://weather.nmsu.edu
Temperature sensor and radiation shield
The Water Balance Spread Sheet
• Inputs
• Climate data, paste into spread sheet
• Soil water holding capacity inch/ft
• Irrigation amount applied at each irrigation.
• Output – Date to irrigate on
The Water Balance Spread Sheet
Apple Irrigation
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
0 50 100 150 200
Days since bud break
Eva
po
tra
nsp
ira
tio
n
or
irri
ga
tio
n (
inch
es)
Irrigations Evapotranspiration
73161
Conclusion
• The water balance-check book method can be used to schedule irrigations for Apples.
• The water use of Apples can be calculated from climate data, and this is all that is needed to apply the correct amount of water at the correct time
• The check book method can also determine the decrease in yield and amount of water stress when time between irrigation is to long.