Malheur Experiment Station
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Information for Sustainable Agriculture
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EFFECT OF SHORT-DURATION WATER STRESS ON ONION SINGLE CENTEREDNESS AND TRANSLUCENT SCALE
Clinton C. Shock, Erik Feibert, and Lamont Saunders
Malheur Experiment Station
Oregon State University
Ontario, OR, 2003
Introduction
In earlier trials we have shown that onion yield and grade are
very responsive to soil water (Shock et al. 1998b, 2000). Using a
high-frequency automated drip-irrigation system, the soil water
potential at 8-inch depth that resulted in maximum onion yield, grade,
and quality after storage was determined to be -20 kPa. Short term
water stress, caused by irrigation errors, could result in internal
bulb defects such as multiple centers and translucent scale. This trial
tested the effects of short-duration water stress at different times
during the season on onion single centeredness and translucent scale.
Materials and Methods
The onions were grown at the Malheur Experiment Station,
Ontario, Oregon on an Owyhee silt loam previously planted to wheat.
Onion (cv. 'Vaquero', Sunseeds, Morgan Hill, CA) was planted in two
double rows, spaced 22 inches apart (center of double row to center of
double row) on 44-inch beds on March 17, 2003. The two rows in the
double row were spaced 3 inches apart. Onion was planted at 150,000
seeds/acre. Drip tape (T-tape, T-systems International,
San Diego, CA) was laid at 6-inch depth between the two double onion
rows on March 28. The distance between the tape and the double row was
11 inches. The drip tape had emitters spaced 12 inches apart and a flow rate of 0.22 gal/min/100 ft.
Immediately after planting the onion rows received 3.7 oz of
Lorsban 15G per 1,000 ft of row (0.82 lb ai/acre), and the soil surface
was rolled. Onion emergence started on April 7. The trial was irrigated on April 14 with a
minisprinkler system (R10 Turbo Rotator, Nelson Irrigation Corp., Walla
Walla, WA) for even stand establishment. Risers were spaced 25 ft apart
along the flexible polyethylene hose laterals that were spaced 30 ft
apart.
The experimental design was a randomized complete
block with five replicates. There were five treatments that consisted
of four timings of short-duration water stress and an unstressed check.
The water stress was applied by turning the water off to all plots in a
treatment until the average soil water potential at 8-inch depth for
the treatment reached -60 kPa; at this point, the water to all plots in
that treatment was turned on again. Each treatment was stressed once
during the season. The four timings for the stress treatments were:
four-leaf stage (water off June 2, water back on June 10), early
six-leaf stage (water off June 16, water back on June 21), late
six-leaf stage (water off June 26, water back on July 2) , and
eight-leaf stage (water off July 7, water back on July 11).
Soil water potential was measured in each plot
with four granular matrix sensors (GMS, Watermark Soil Moisture Sensors
Model 200SS, Irrometer Co., Riverside, CA) installed at 8-inch depth in
the center of the double row. Sensors were calibrated to swp (Shock et
al. 1998a). The GMS were connected to the datalogger with three
multiplexers (AM 410 multiplexer, Campbell Scientific, Logan, UT). The
datalogger read the sensors and recorded the soil water potential every
hour. The irrigations were controlled by the datalogger using a relay
driver (A21 REL, Campbell Scientific, Logan, UT) connected to a
solenoid valve. Irrigation decisions were made every 12 hours by the
datalogger: if the average soil water potential at 8-inch depth in the
unstressed treatment plots was -20 kPa or less the field was irrigated
for 4 hours. The pressure in the drip lines was maintained at 10 psi by
a pressure regulator. Irrigations were terminated on September 2.
Onion tissue was sampled for nutrient
content on June 4 and 19. The roots from four onion plants in each
check plot were washed with deionized water and analyzed for nutrient
content by Western Labs, Parma, ID. The onions in all treatments were
fertilized according to the nutrient analyses. Fertilizer was applied
through the drip tape: ammonium sulfate at 25 lb N/acre on May 30, urea
ammonium nitrate solution at 25 lb N/acre on June 5, June 16, and June
25, and zinc chelate at 0.25 lb Zn/acre and copper chelate at 0.2 lb
Cu/acre on June 25.
Roundup at 24 oz/acre was sprayed on March 28. The field had Prowl (1lb
ai/acre) broadcast on April 21 for postemergence weed control.
Approximately 0.4 inch of water was applied through the minisprinkler
system on April 21 to incorporate the Prowl. The field had
Buctril at 0.12 lb ai/acre and Poast at 0.4 lb ai/acre applied on April
28. Thrips were controlled with one aerial application of Warrior on
June 5 and two aerial applications of Warrior (0.03 lb ai/acre) plus
Lannate (0.4 lb ai/acre) on July 16 and August 4.
On September 11 the onions
were lifted to field cure. On September 17, onions in the central 40 ft
of the middle two double rows in each subplot were topped and bagged.
The bags were placed into storage on September 29. The storage shed was managed to maintain an
air temperature of approximately 34°F. On December 11 the onions were graded.
Bulbs were separated according to quality: bulbs without blemishes (No. 1s), double bulbs (No. 2s),
neck rot (bulbs infected with the fungus Botrytis allii in the neck or side),
plate rot (bulbs infected with the fungus Fusarium oxysporum),
and black mold (bulbs infected with the fungus Aspergillus niger).
The No. 1 bulbs were graded according to diameter: small (<2¼
inch), medium (2¼-3 inches), jumbo (3-4 inches), colossal (4-4¼ inches),
and supercolossal (>4¼ inches).
Bulb counts per 50 lb of supercolossal onions were determined for each
plot of every variety by weighing and counting all supercolossal bulbs
during grading.
After grading, 50 bulbs ranging in diameter from 3.5 to
4.25 inches from each plot were rated for single centers and
translucent scale. The onions were cut equatorially through the bulb
middle and, if multiple centered, the long axis of the inside diameter
of the first single ring was measured. These multiple-centered onions
were ranked according to the diameter of the first single ring: "small
double" had diameters <1½ inch, "intermediate double" had
diameters from 1½-2¼ inches, and "blowout" had diameters
>2¼ inches. Single-centered onions were classed as a
"bullet". Onions were considered functionally single centered for
processing if they were a "bullet" or "small double." The number and
location of translucent scales in each bulb was also recorded.
Results and Discussion
The soil water potential at 8-inch depth during the stress
treatments reached values lower than the planned -60 kPa (Fig. 1).
Irrigations for the plots being stressed were restarted as soon as the
soil water potential reached -60 kPa. However, because the drip tape
was located 11 inches from the soil moisture sensors, there was a short
delay between the onset of irrigation and when the wetting front
reached the sensors, when the soil moisture sensors began responding to
the irrigations.
Water stress at the four-leaf (early June) and at the six-leaf
(mid-June) stages resulted in fewer bullet single-centered and
functionally single-centered onions than the unstressed check (Table
1). Water stress at the later stages did not affect onion
single-centeredness. Water stress at the four-leaf stage resulted in
higher percentage of blowout multiple centered onions. Water stress did
not affect translucent scale. The level of translucent scale was very
low, with all of the treatments having less than 1 percent of bulbs
with translucent scales. In contrast to a previous study (Hegde 1986),
the short-duration water stress in this trial did not affect onion
yield or grade. Onion yield and size were reduced by short-duration
water stress to -85 kPa, with the onions otherwise irrigated at -45 kPa
(Hegde 1986). In the study by Hegde, the soil water potential at which
the onions were irrigated was drier (-45 kPa) than in this study (-20
kPa) and the irrigation frequency was much lower, possibly causing the
difference in results. The average onion yields in this trial were: 860
cwt/acre total yield, 837 cwt/acre marketable yield, 8 cwt/acre super
colossal yield, 155 cwt/acre colossal yield, and 652 cwt/acre jumbo
yield.
References
Hegde, D.M. 1986. Effect of irrigation
regimes on dry matter production, yield, nutrient uptake and water use
of onion. Indian J. Agronomy 31:343-348.
Shock, C.C., J.M. Barnum, and M. Seddigh. 1998a. Calibration of
Watermark Soil Moisture Sensors for irrigation management. Pages
139-146 in Proceedings of the International Irrigation Show, Irrigation Association,
San Diego, CA.
Shock, C.C., E.B.G. Feibert, and L.D. Saunders.
1998b. Onion yield and quality affected by soil water potential as
irrigation threshold. HortScience 33:188-191.
Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2000. Irrigation criteria for drip-irrigated
onions. HortScience 35:63-66.
Table 1. Onion multiple-center rating response to timing of
water stress, Malheur Experiment Station, Oregon State University,
Ontario, OR, 2003.
Water stress timing |
Blowout |
Intermediate double |
Small double |
Bullet |
Functionally single centered "Bullet + small double" |
|
-------------------------------- % ---------------------------------- |
Check, no stress |
2.5 |
14.0 |
14 |
69.5 |
83.5 |
4-leaf stage, early June |
10.5 |
20.0 |
17 |
52.5 |
69.5 |
6-leaf stage, mid-June |
4.5 |
26.0 |
15.5 |
54.0 |
69.5 |
6-leaf stage, late June |
1.5 |
12.0 |
21.5 |
65.0 |
86.5 |
8-leaf stage, early July |
3.5 |
18.5 |
16.0 |
62.0 |
78.0 |
LSD (0.05) |
3.7 |
7.9 |
NS |
10.9 |
8.5 |
Figure 1. Soil water potential for onions irrigated at -20 kPa
with an automated drip irrigation system and submitted to
short-duration water stress, Malheur Experiment Station, Oregon State
University, Ontario, OR, 2003.
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For
additional information about the Malheur Agricultural Experiment
Station, please send an e-mail request to:
Dr. Clinton C. Shock
Clinton.Shock@oregonstate.edu
Malheur Agricultural Experiment
Station
595 Onion Avenue
Ontario, OR 97914
(541) 889-2174
FAX (541) 889-7831
Last updated
Monday August 30, 2010 .
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