Malheur Experiment Station
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Information for Sustainable Agriculture
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EFFECT OF PHOSPHITE FERTILIZER FORMULATIONS ON ONION YIELD AND QUALITY
Clinton C. Shock, Michael Lewis, Erik Feibert, and Lamont Saunders
Malheur Experiment Station
Oregon State University
Ontario, OR, 2003
Introduction
Biagro Western (Visalia, CA) manufactures formulations of
phosphite fertilizer. They claim that phosphorus (P) in the form of
phosphite (PO3) is to be more easily absorbed by plants than P in the form of
phosphate (PO4). This trial tested three phosphite fertilizer formulations for their
effect on onion plant P content, and onion yield and grade.
Materials and Methods
The onions were grown at the Malheur Experiment Station,
Ontario, Oregon on an Owyhee silt loam previously planted to wheat. In
the fall of 2002, the wheat stubble was shredded, and the field was
disked, irrigated, ripped, moldboard-plowed, roller-harrowed, fumigated
with Telone C-17 at 20 gal/acre, and bedded. Soil analysis indicated
the need for 100 lb P2O5/acre, 150 lb K /acre, 6
lb Mn/acre, 2 lb Cu/acre, and 1 lb B/acre, which was broadcast in the
fall. A soil sample taken on May 9 showed a pH of 7.7, 1.4 percent
organic matter, 0.2 percent lime, 20 ppm nitrate-N, 29 ppm P (Olsen
test, sodium bicarbonate extractant), and 216 ppm K.
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) in 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 four treatments: an untreated
check and three fertilizer formulations. The fertilizer formulations
were manufactured by Biagro Western and were Magnum Nutri-phite
(2-40-16) foliar (3 pints/acre/application), Sulfone Nutri-phite
(5-20-15-14) foliar (3 lb/acre/application), and P Soil Hi-Grade (0-60-0) drip injected
(2 quarts/acre/application). Each fertilizer
treatment was applied three times as follows: first application: bulb
at 0.5 inch (June 10); second application: 3 weeks after first
application (July 1); third application: 6 weeks after first
application (July 17). The two foliar applied formulations were applied
at 40 gal/acre with a backpack sprayer with four 8004 nozzles at 30
PSI. The drip-injected formulation was applied through the drip tape at
an injection rate of 2.5 percent using a Dosmatic A30 injector
(Dosmatic USA, Carrolton, TX). All treatments including the check
received standard fertilizer applications based on soil and tissue
analyses.
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, Idaho. The onions in all treatments
were fertilized according to the nutrient analyses. Onion root P
concentration for the check treatment was 0.40 and 0.59 percent on June
4 and 19, respectively. 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, 16, and 25; and zinc chelate at
0.25 lb Zn/acre and copper chelate at 0.2 lb Cu/acre on June 25.
Onion tissue was also sampled from all treatments for comparison
of P contents on July 3, July 19, and August 8. Five onion plants from
outside the harvest area from each plot of each treatment were combined
to make one sample per treatment. Each sample was separated into roots,
bulbs, and leaves. The roots and leaves were weighed, dried in a
forced-air oven at 150°F for 4 days and weighed. The bulbs were
weighed and shredded. A subsample of the shredded bulbs was weighed,
dried in a forced-air oven at 150°F for 4 days, and weighed. The
dried roots, bulbs, and leaves were ground and analyzed for total P
content.
The field was irrigated
automatically twice per day based on soil water potential readings.
Soil water potential was measured 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 in each of four adjacent plots. Sensors were calibrated to swp
(Shock et al. 1998). The GMS were connected to a 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 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.
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 inches), 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 to 2¼ inches, and "blowout" had
diameters >2 ¼ inch 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 automated drip-irrigation system maintained
the soil water potential close to -20 kPa during the season (Fig. 1).
The onions treated with the three phosphite fertilizer formulations had
increased levels of bulb P on the first two sampling dates (Table 1).
Definitive conclusions on differences in tissue P levels between
treatments cannot be made due to a lack of tissue sample replication.
There was no significant difference in onion
yield or grade between the phosphite fertilizer formulations and the
check (Table 2). There was no significant difference in onion single
centeredness between the phosphite fertilizer formulations and the
check (Table 3).
The May 9 soil test showed 29 ppm P. According to
the "Nutrient Management Guide for Onions in the Pacific Northwest"
(Sullivan et al. 2001), P fertilizer would not have been necessary.
Although limited data exist to interpret onion tissue P, Sullivan et
al. (2001) suggests a sufficiency range from 0.2 to 0.35 percent root
P. Western Labs uses a sufficiency range for onion root P of 0.32 to
0.7 percent. Root P for the check treatment onions was 0.40 percent on
June 4 and 0.59 percent on June 19.
To increase the probability of onion response to
the phosphite fertilizers, this trial should have been conducted in a
field without fall-applied P, and preferably on a soil more prone to P
deficiencies, such as a Nyssa silt loam. In addition, onions are more
prone to P deficiency early in the season when the soils are colder,
which hinders the uptake of P by the roots. Despite the preexisting
limitations of the field used in this trial, the manufacturer opted for
the site and for the late applications.
References
Shock, C.C., J.M. Barnum, and M. Seddigh. 1998. Calibration of
Watermark Soil Moisture Sensors for irrigation management. Pages
139-146 in Proceedings of the International Irrigation Show, Irrigation Association, San
Diego, CA.
Sullivan, D.M., B.D. Brown, C.C. Shock, D.A. Horneck, R.G. Stevens, G.Q. Pelter, and E.B.G.
Feibert. 2001. Nutrient Management for onions in the Pacific Northwest. Pacific Northwest
Extension Publication PNW 546. 26p.
Table 1. Onion tissue phosphorus levels (percent dry weight) for onions
treated with three phosphite fertilizer formulations, Malheur
Experiment Station, Oregon State University, Ontario, OR, 2003.
|
|
July 3 |
July 19 |
August 8 |
Treatment |
Roots |
Bulbs |
Leaves |
Roots |
Bulbs |
Leaves |
Roots |
Bulbs |
Leaves |
Check |
0.66 |
0.35 |
0.44 |
0.42 |
0.52 |
0.31 |
0.49 |
0.48 |
0.19 |
Magnum Nutri-Phite |
0.66 |
0.59 |
0.46 |
0.47 |
0.76 |
0.35 |
0.58 |
0.51 |
0.27 |
Sulfone Nutri-Phite |
0.61 |
0.57 |
0.41 |
0.56 |
0.61 |
0.35 |
0.42 |
0.45 |
0.23 |
P Soil Hi-Grade |
0.65 |
0.57 |
0.45 |
0.49 |
0.50 |
0.36 |
0.56 |
0.48 |
0.24 |
Table 2. Onion yield and grade response to three phosphite fertilizer
formulations, Malheur Experiment Station, Oregon State University,
Ontario, OR, 2003.
|
|
Total yield |
Marketable yield by grade |
|
Non-marketable yield |
Treatment |
Total |
>4¼ in |
4-4¼ in |
3-4 in |
2¼-3 in |
|
Rot |
No. 2s |
Small |
|
--------------------------- cwt/acre --------------------------- |
|
% |
-- cwt/acre -- |
Check |
837.6 |
815.2 |
9.7 |
152.3 |
632.6 |
20.6 |
|
2.1 |
2.3 |
5.4 |
Magnum Nutri-Phite |
778.3 |
754.3 |
5.6 |
128.9 |
597.5 |
22.3 |
|
2.5 |
1.2 |
4.2 |
Sulfone Nutri-Phite |
871.0 |
849.6 |
13.0 |
167.6 |
650.2 |
18.8 |
|
2.2 |
3.1 |
2.3 |
P Soil Hi-Grade |
839.5 |
810.3 |
7.0 |
163.4 |
620.8 |
19.1 |
|
3.1 |
3.5 |
3.8 |
| LSD (0.05) |
NS |
NS |
NS |
NS |
NS |
NS |
|
NS |
NS |
NS |
Table 3. Single-center rating for
onions treated with three phosphite fertilizer formulations, Malheur
Experiment Station, Oregon State University, Ontario, OR, 2003.
| Treatment |
Blowout |
Intermediate double |
Small double |
Bullet |
Functionally single centered "Bullet + small double" |
|
----------------------------------- % ------------------------------------- |
| Check |
2.5 |
14 |
14 |
69.5 |
83.5 |
| Magnum Nutri-Phite |
4.4 |
17.2 |
18.8 |
59.6 |
78.4 |
| Sulfone Nutri-Phite |
2.8 |
13.2 |
17.6 |
66.4 |
84 |
| P Soil Hi-Grade |
6.4 |
15.6 |
18.8 |
59.2 |
78 |
| LSD (0.05) |
NS |
NS |
NS |
NS |
NS |
Figure 1. Soil water potential at 8-inch depth for onions irrigated
with an automated subsurface drip-irrigation system, 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
Friday July 30, 2004 .
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