Malheur Experiment Station Information for Sustainable Agriculture

AuxiGro Field Research on Potato

Eric P. Eldredge and Clinton C. Shock
Malheur Experiment Station
Oregon State University
Ontario, OR, 1998

Introduction

This is the second year of testing AuxiGro on potato at Malheur Experiment Station. In 1997, AuxiGro was applied to three varieties of potato grown under sprinkler irrigation. In 1998 AuxiGro was applied to the variety Umatilla Russet grown with drip irrigation. The purpose of this trial was to test AuxiGro at several rates applied at three potato-plant developmental stages: emergence, tuber initiation, and after canopy closure. Potential effects of AuxiGro were measured on petiole nitrate and on tuber yield, grade, and processing quality following harvest.

Materials and Methods

Field Preparation and Planting. The 1998 study was conducted on an Owyhee silt loam which had been in winter wheat the previous year. When the wheat was harvested in August 1997, and the stubble was flailed. On September 3, the stubble was disked twice, and on September 29, 100 lb P₂O₅ and 20 lb N/acre were broadcast. On October 1, 1997, the field was fumigated with 22 gal/acre of Telone II injected by a commercial applicator and the soil was bedded into 36-in rows.

The top two ft of soil was sampled March 16, 1998, and a complete analysis was performed by Western Labs, Parma, ID. On April 15, 1998, the field was sprayed with Roundup to control volunteer wheat. Certified Umatilla Russet potato seed was cut and treated with Mancozeb at Ontario Produce then planted May 6 on 9-in spacing, 10 in deep, in 36-in rows. A two-row-per bed configuration was started at planting by leaving off the center furrowing shovel from the Parma two-row planter. On May 7, the rows were side dressed with urea prills at 23 lb N/acre. Then on May 8 the beds were harrowed one pass each way with a spike-tooth, bed harrow and winged shovels, dragging a 12 ft vee of 5/8 in chain to pull soil into the bed center. On May 11, one pass was made going each way with winged shovels on a tool bar to deepen the furrows.

Weed Control and Late Blight Control. By May 19 the potatoes had not yet emerged, and Prowl at 1 lb ai/acre plus Dual at 2 lb ai/acre in 30 gal/acre water were applied for weed control using a boom sprayer on a tractor. On May 20 one pass to incorporate the herbicides was made with a bed harrow with winged shovels, dragging chain, followed by a second pass with the same implement with a shank mounted to lay the drip tube 3 in deep, centered between the two rows on each bed. Potato emergence began May 31, with some variability, probably due to 4.55 in of rain in May.

On June 4, a postemergence herbicide treatment of Matrix at 1 oz/acre, Sencor at 1 pt/acre, plus BreakThru at 1 pt/100 gal spray was applied in 30 gal/acre of water. On June 9, the first aerial, late-blight control spray, Bravo Weatherstik, was applied. On June 18, the next scheduled aerial application for late blight control used Dithane at 1.6 qt/acre plus 8 oz Adhere and 12 oz BreakThru/100 gal. On July 3, another Dithane aerial application was made for late blight control. On July 5, an emergency Dithane plus Kocide aerial application was made to keep hail-defoliated vines from rotting before the field could dry out and to protect the new growth from axillary buds. Routine applications of fungicide continued with a Bravo aerial application on July 11.

AuxiGro Treatments. The seven treatments consisted of an untreated check, and variable rates of AuxiGro applied at various at plant development stages (Table 1). The treatments were chosen to expose developing potato foliage to different rates of AuxiGro from emergence, testing the hypothesis that AuxiGro could help potato plants cope with stress. Developmental stages selected were early postemergence, tuber initiation, and 3 weeks after tuber initiation. Because of the hail damage, the late treatment was delayed an additional week to 4 weeks after tuber initiation.

On June 10, the postemergence AuxiGro was applied with water at 40 gal/acre with a 6 nozzle boom on a CO₂ sprayer. TeeJet VS ER 8004 flat fan nozzles were used, and a silicone based surfactant (BreakThru at 0.05 percent) was used for all AuxiGro applications. Plants were mostly about 6 in tall by 6 in wide, with a few late-emerging plants just breaking through the soil crust. No rain fell after this application until 0.08 in on June 12.

On June 12, the first irrigation was made through the drip system for 4 hours, applying 0.13 acre-in/acre. On June 15 the second drip irrigation was a 4 hour set and applied 0.15 acre-in/acre. Subsequent irrigations were scheduled using Watermark sensors placed in the root zone of the crop. Watermark sensors were monitored daily.

Plots were 30-ft long by 4 rows wide, with row 1 serving as the border between adjacent plots, and a 5-ft alley between replications. The design was a randomized complete block with 7 treatments and 6 replications. AuxiGro treatments were applied to rows 2, 3, and 4 of the treated plots at each application date. Petiole samples were taken from plants in rows 2 and 4, leaving row 3 undisturbed season-long for tuber harvest.

On June 17, one week after the first AuxiGro application, the first petiole sample was taken of 20 petioles per plot from plants in rows 2 and 4 only. A soil sample was also taken from the top foot and second foot from all plots in replicates 1, 3, and 5. Tuber initiation AuxiGro treatments 2-7 were applied June 17, using the same equipment and methodology as before. The plants had 3 to 4 stems per hill, tubers ranged from as large as a pea down to stolons just hooking. Plants had 11 leaves per stem and terminal flower buds had formed but no blooms were showing. Stems were 12-in tall. No rain fell after this treatment until 0.05 in June 23.

Nine days later, on June 26, petioles were sampled again and taken to Western Labs for nitrate-N analysis for each plot, and a complete analysis of bulked tissue from all plots. On July 3 , in response to the results of the first, pre-application, petiole test, micronutrients Cu at 0.41, Zn at 0.41, Mn at 0.17, B at 0.5, and S at 16.4 lb/acre were injected through the drip system, then the lines were flushed. On July 4 a hail storm dropped up to 1/2-in hailstones for one half hour with strong wind and heavy rain, nearly defoliating the potatoes.

On July 14, after an additional week delay to allow regrowth of the foliage, the last AuxiGro applications were made. On July 22, samples of 20 petioles per plot were taken from plants in rows two and four of each plot for nitrate N analysis. No rain fell following this AuxiGro application until 0.01 in July 30.

On September 25, the vines were removed by flail. On October 8-9, the tubers were lifted with a two-row digger and the tubers from the middle row were picked up by hand. Potatoes were graded on October 16-19. At grading, a 20-tuber sample of U.S. Number One tubers from each plot was placed into storage. Storage temperature was slowly lowered to 47 ^oF. On January 8, 1999, the specific gravity and fry color of 10 tubers from each sample were measured.

Results and Discussion

No visual differences were seen in any of the plots or plants during the conduct of this study. Plots were carefully scrutinized, especially at the petiole sampling dates. Before the hailstorm, the potato field was in bloom and a very uniform bloom and canopy was noted across not only the study area but also the adjacent field of drip-irrigated Umatilla. When Dr. Kaake visited the plots on July 20, after the potato plant regrowth from the hail damage, no differences were visible among any of the plots.

The hail storm was a major factor influencing the outcome of this experiment because from July 4th on, the study was conducted on the regrowth after the hail damage. The second overriding factor in this experiment was the unusual heat in July, August, and September. The growing season started out cooler and wetter than normal. The month of May had 4.55 in of precipitation compared to the 50-year mean of 1.02 in. May had 29 percent fewer and June had 18 percent fewer growing degree days (50-86 ⁰F) than the previous 10 year means. In contrast, the months of July and August were hotter than normal. The Malheur Experiment Station NOA weather station recorded 11 days with maximum air temperatures of 100 ⁰F or higher compared to the 50-year mean of 5 days. There were far more degree days in the above optimal range (86 to 104 ⁰F) in 1998 compared to the previous 8 year mean; 70 percent more in July and 29 percent more in August. The hot weather in July and August was sub-optimal for potato, especially for the regrowth of hail-damaged potatoes.

Petiole sampling showed no significant differences by treatment for any of the three sampling dates (Table 1). Soil sampling showed adequate fertility for potato production, and any deficiencies detected by soil or petiole sampling were promptly corrected with supplemental fertilizer applications through the drip system.

Irrigation management through the hottest part of the summer minimized water stress to the potato plants. Estimated ET_c for potato calculated using the U.S. Department of the Interior Bureau of Reclamation AgriMet station 400 yd from the study site was 25.1 acre-in/acre for June 1 through September 21. Water applied through the drip system totaled 12.9 acre-in/acre plus 2.44 in of rain = 15.34 acre-in/acre for the period June 1 through September 21. The discrepancy between AgriMet ET_c and irrigation plus rainfall was understandable because of more efficient water application and less mid-season potato foliage to transpire water. Although less water was applied through the drip system than the calculated potato ET_c, the soil beneath the drip tape remained wet through the growing season. At no time were any plants observed to wilt, although on afternoons with temperatures over 100 ^oF there was leaf curling response observed uniformly across the field.

Yield and grade responded to hail injury and excess heat with reduced overall yield, decreased percentage of U.S. Number Ones, and increased production of small tubers. Umatilla Russet typically would produce over 400 cwt/acre at MES but averaged only 363 cwt/acre in this study (Table 2). Number Ones would typically be 65 percent or more, but in this study they averaged only 53 percent. Despite the multiple stresses of cold-wet soil during emergence, hail damage at full bloom, and excessive heat through tuber bulking, the fry color of Umatilla Russet tuber stem-ends remained light, averaging 42 percent light reflectance and tuber specific gravity averaged 1.0810 out of storage in January.

AuxiGro treatments had no measurable effect on any grade or quality parameter in this study at the 5 percent level (LSD = 0.05). Even at the 10 percent level, the only difference was in the yield of 4 to 6 oz U.S. Number Ones, with treatment 4. Treatment 4, the high (7.5 oz/acre) rate of AuxiGro, applied twice, (at emergence and again at tuber initiation) resulted in significantly (LSD (0.10) = 15.53 cwt/acre) more small U.S. Number One tubers than treatments 3, 5, and 7, but was not significantly different from the untreated check. The yield of large U.S. Number One tubers for that treatment, while not significant even at the 10 percent level, was reduced.

In conclusion, AuxiGro had no measurable effect on the potatoes in this trial.

Table 1. Results of petiole nitrate sampling in AuxiGro treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 1998.

		Petiole nitrate by date
	Treatment	6/17	6/26	7/22
		---------------------------ppm-------------------------
1	Untreated Check	27345	20110	12058
2	2.5 oz/acre AuxiGro at emergence + 2.5oz at tuber initiation	26025	21543	13968
3	5.0 oz/acre AuxiGro at emergence + 5.0 oz at tuber initiation	26423	22235	13165
4	7.5 oz/acre AuxiGro at emergence + 7.5oz at tuber initiation	24348	20888	13265
5	5.0 oz/acre AuxiGro at tuber initiation	26069	20388	15729
6	2.5 oz/acre AuxiGro at tuber initiation + 2.5 oz 4 weeks later	26952	20958	14341
7	7.5 oz/acre AuxiGro at tuber initiation +7.5 oz 4 weeks later	26996	19505	12014
Mean		26308	20804	13406
LSD (0.05)		NS	NS	NS

Table 2. Test of AuxiGro on Umatilla Russet potato grade distribution, yield, and processing quality. Potatoes were grown under drip irrigation, Malheur Experiment Station, Oregon State University, Ontario, OR, 1998.

	U.S. Number Ones					Marketable				Total	Percent	Specific	Basal	Apical
treatment	4-6 oz	6-12 oz	> 12 oz	Total	No. Twos	yield	<4 oz	culls	decayed	yield	No. ones	gravity	fry color	fry color
	-----------------------------------------------------cwt/acre-------------------------------------------------------------------										percent	s. g.	percent reflectance
1	73.6	107.6	12.1	193	81.7	275	77.3	6.2	1.0	359	54	1.0825	40.3	45.5
2	82.1	101.0	7.5	191	63.3	254	99.9	8.8	0.2	363	52	1.0800	44.0	46.4
3	71.4	111.0	12.6	195	78.5	274	83.8	5.5	0.0	363	53	1.0800	43.5	45.8
4	88.5	101.5	6.0	196	80.7	277	89.3	2.6	0.7	369	53	1.0823	40.9	46.5
5	61.0	109.9	18.1	189	82.7	272	81.6	2.7	0.2	356	52	1.0791	41.6	44.9
6	75.2	112.4	13.5	201	72.6	274	72.8	8.2	0.0	355	57	1.0821	41.2	46.2
7	65.9	116.4	11.2	193	97.9	291	79.9	4.6	1.8	378	51	1.0810	41.6	45.2
Mean	73.95	108.56	11.58	194.1	79.62	273.7	83.5	5.52	0.54	363.3	53.2	1.0810	41.9	45.8
LSD (0.05)	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
NS LSD (0.10)	15.53	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS

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