Transcript Scheduling irrigations for apple trees using climate data Ted Sammis Go to Home.

Scheduling irrigations for apple trees
using climate data
Ted Sammis
Go to Home
The Water Budget Method
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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
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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
0.4
0.35
Eto inch/day
0.3
0.25
0.2
0.15
0.1
0.05
0
11/1/1998
2/9/1999
5/20/1999
8/28/1999
Date
12/6/1999
3/15/2000
Crop coefficient scaling function for
trees based on projected area
Crop Coefficient Scaling factor
1.2
1
y = 1.1728x 0.5845
R2 = 0.9957
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
Shaded area/tree spacing
0.8
1
Calculation of Evapotranspiration
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Potential Et= 0.3 inches / day
Et= K*PET
K= 0.8
Et= 0.8* 0.3 = .24 inch/day
Daily Apple
Evapotranspiration
Evapotranspiration (inches/day)
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
50
100
Days since bud break
150
200
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
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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
Evapotranspiration or
irrigation (inches)
35.00
30.00
25.00
20.00
15.00
73161
10.00
5.00
0.00
0
50
100
150
Days since bud break
Irrigations
Evapotranspiration
200
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.