July/August 2021 - 26

The Potato Association of America mission statement: The PAA and
its allied associations must strongly support the private sector through
Extension, research and commercialization efforts aimed at enhancing
the role of the potato as the premier food source for the 21st century.
Maximizing grower return with
proper late-season irrigation
By Francisco Gonzalez, Zach Holden, Rudy Garca
and Mark J. Pavek
Potato Association of America
W
ithout irrigation, profitable potato production
would be unlikely in low rainfall regions. Proper
season-long soil moisture is the key to maximizing
tuber yield, quality and grower return.
In well-drained soils, it is difficult to over-irrigate potatoes
during early-season rapid canopy growth, as healthy plants
consume water almost as quickly as it is applied.
As the potato canopy matures mid-season, plant
consumption drops significantly, but proper irrigation is still
essential. Once the potato canopy is fully developed, about
mid-July in central Washington, the plant shifts its priority
from vegetative growth to tuber bulking.
Between the plant growth stages of tuber bulking to
maturity, we researched these questions:
1. How much water does a fully developed plant (peak of
canopy and root mass) need?
2. At what point does late season irrigation become excessive?
3. Do cultivars respond similarly?
RESEARCH METHODS
Each year from 2018-20, we planted five potato cultivars -
Alturas, Clearwater Russet, Ranger Russet, Russet Burbank and
Umatilla Russet - near Othello, Washington, and produced
them using grower-standard irrigation between emergence
and midseason.
Grower-standard irrigation was delivered at 100% of
evapotranspiration (ET), estimated using the Washington
State University's (WSU) irrigation scheduler web-based
program.
Once the plant canopy and roots peaked in growth -
estimated at 1500-growing degree days (base temperature
of 45°F, with upper limit of 95°F), which was between 95 and
105 days after planting (DAP) - five levels of irrigation were
applied on all cultivars: 120% ET, 100% ET (considered the
grower standard), 80% ET, 60% ET and 40% ET. The irrigation
treatments continued until vines were killed or dead (~150
DAP), and the soil was kept moist until harvest. Tuber yield
and quality were assessed and grower return calculated using
a standard french-fry processing contract.
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Spudman.com
Figure 1
RESULTS AND DISCUSSION
(Due to page space considerations, not all data is shown.)
Total yield for the four non-Alturas cultivars peaked at 100%
ET, while Alturas peaked at 80% ET. Irrigation exceeding 100%
ET failed to significantly improve total yield across cultivars.
Late-season irrigation levels below 100% ET led to total
yield reductions of up to 26% across cultivars. Process
adjusted gross was optimized by irrigating between 80% ET
and 100% ET for all cultivars (see Figure 1).
Alturas and Umatilla Russet gross return peaked when lateseason
irrigation was applied at or above 80% ET.
Gross return was maximized with 100% of ET replacement
for Clearwater Russet, Ranger Russet and Russet Burbank
(Figure 1).
At 40% ET, gross return was reduced by up to 38% for
Clearwater Russet and less than 30% for the other cultivars.
Process adjusted gross was typically reduced due to a loss in
marketable yield and tuber quality.
10 Alturas
-10
-20
-30
-40
10
-10
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-30
-40
10
-10
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-30
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40
60
80
100
120
40
60
80
100
Late season irrigation level (% evapotranspiration)
120
Russet Burbank
Umatilla Russet
Clearwater Russet
Ranger Russet
Processing gross value, grower return
(% Differenece from the 100% treatment)
http://www.Spudman.com
July/August 2021

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