Malheur Experiment Station

Information for Sustainable Agriculture

Potato Tuber Bulking Rate and Processing Quality for Early Harvest

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

Introduction

The six potato varieties ‘Alturas’, ‘Ranger Russet’, ‘Russet Burbank’, ‘Shepody’, ‘Umatilla Russet’, ‘Wallowa Russet’, and the five numbered clones, ‘A9014-2’, ‘A9045-7’, ‘A90586-11’, ‘A92294-6’, and ‘A93157-6LS’ were compared for tuber yield, size distribution, and processing quality at six harvest dates. Russet Burbank, Shepody and Ranger are currently grown in the Treasure Valley for processing and served as the check varieties. Umatilla and Wallowa Russet are new releases from Oregon State University (OSU) that have demonstrated yield, grade, and processing quality superior to Russet Burbank, Shepody, and Ranger Russet in some trials. The numbered clones have performed well at Ontario in previous variety trials, including the Western Regional Early Harvest Trial, over several years. The first objective of this study was to test potato cultivars that are currently available, and some numbered clones that may soon be released, for very early harvest, compared to the varieties currently grown for early harvest for processing. The second objective was to determine if any of these clones would continue to bulk tubers late in the season.

Materials and Methods

The soil was Owyhee silt loam where winter wheat was the previous crop. The wheat stubble was flailed and the field was irrigated and disked. A soil test taken September 9, 2002 showed 18 ppm NO₃, 18 ppm P, 306 ppm K, organic matter 2.2 percent, and pH 7.6. Fall fertilizer consisting of 21 lb N/acre, 100 lb P₂O₅/acre, 60 lb K₂O/acre, 60 lb S/acre, 30 lb Mg/acre, 4 lb Zn/acre, 2 lb Cu/acre, 1 lb Mn/acre, and 1 lb B/acre was broadcast. The field was ripped, Telone II was injected at 25 gal/acre, and the field was bedded on 36-inch row spacing.

The experiment had a split-plot design, with the six harvest dates as the main plots replicated four times and with varieties randomized as sub-plots within each main plot. This was accomplished by planting the rows so that each harvest date pass through each replicate would include all of the varieties.

Potato seed was obtained from the OSU Potato Variety Development program at Powell Butte, and placed into storage at 42° F. Seed of the cultivar Ranger Russet was donated by J.R. Simplot Co., Caldwell, ID, from commercial certified seed produced in eastern Idaho. Seed tubers were cut by hand into approximately 2 oz pieces, treated with Tops MZ + Gaucho seed treating dust, and counted into bags of 15 seed pieces for each row of the two-row plots.

The potato clones were planted on April 10 with rows spaced 36 inches apart and 9-inch spacing between seed pieces in the row. The soil condition was excellent, with good tilth and good soil moisture. The soil temperature at the 10-inch seed piece depth was almost 50° F.

A two-row per bed configuration was maintained at planting by leaving off the center furrowing shovel of the two-row planter. On May 5, the beds were formed with a spike harrow with wide shovels that also carried the shank to install a drip tape at 3-inch depth in the top of the bed between the two potato rows. Drip tape was 5/8-inch diameter, 5-mil wall thickness, 12-inch emitter spacing, 0.22-gpm/100 ft flow rate (T-tape, T Systems International, San Diego, CA).

Soil water potential was measured with six Watermark sensors (Irrometer Corp., Riverside, CA) installed in the potato row at the seedpiece depth and connected to an AM400 datalogger (M.K. Hansen, East Wenatchee, WA). Water potential readings were recorded manually from the data logger. Irrigations were scheduled to replace evapotranspiration (Et) estimated by an automated AgriMet (U.S. Bureau of Reclamation, Boise, ID) station located less than 0.25 mile away on the Malheur Experiment Station.

Prowl at 1 lb/acre plus Dual at 2 lb/acre was applied on May 1, before any potato plants had emerged, and was incorporated by a total of 0.42 inch of rain May 3 through 5. Matrix herbicide was applied at 1.25 oz/acre on May 28, and was incorporated by 0.57 inch of rain during subsequent days. Vydate insecticide/nematicide was injected through the drip tape in the first irrigation on June 6 at a rate of 2 pints/acre. During Vydate injection, the irrigation water was acidified to approximately pH 5 by injecting dilute sulfuric acid into the mainline upstream of the Vydate injection.

Fungicide applications to protect the potato foliage from early blight and potential late blight infection started with an aerial application of Ridomil Gold and Bravo at 1.5 pint/acre on June 7, which was repeated on June 25. Bravo fungicide plus liquid sulfur was applied by aerial applicator on July 2, and again on August 8. Sulfur dust was applied by aerial applicator on July 20 at 40 lb S/acre to prevent mite infestation and powdery mildew infection.

Petiole tests were taken every 2 weeks from June 12, and fertilizer was injected into the drip system during irrigation to supply nutrient needs (Table 1). Fertilizer was applied by fertilizer injection into the drip irrigation system only in response to petiole tests.

Tuber initiation was noted on several plants on June 3. On June 19, the first tubers were dug from one row in each replicate. Tubers were sorted by weight and counted. On July 10, tubers were harvested from each replicate, and graded by the U.S. No. 1 and No. 2 processing standard, sorted by weight, and counted in each weight category. Marketable yield for processing was defined as all of the U.S. No. 1 and No. 2 tubers larger than 4 oz. Specific gravity and length-to-width ratio were measured using a sample of 10 tubers. Fry color was determined from a 20 tuber sample from each plot. The subsequent harvests, on July 31, August 21, September 11, and October 2, followed the same procedure as the second harvest.

Yield and quality results data were compared using analysis of variance (Number Cruncher Statistical Systems, Kaysville, UT). Tuber development over time was evaluated using regression of the ratio of polynomials equation:

y = (a+bx+cx²) / (1+dx+ex²) , where y is the yield and x is days after planting (DAP).

Results and Discussion

The 2003 growing season was marked by record heat, with 110° F recorded on July 20, and prolonged heat throughout the summer. Irrigation plus rain supplied 29.7 inches of water, or 94.2 percent of AgriMet Et, which totaled 31.5 inches through the growing season (Fig. 1). The early season moisture deficit indicated that more water should have been applied early in the season to more closely match Et (Fig. 2) starting at 31 DAP. Excessively dry readings may have been partially due to sensor placement.

Potato clones varied in yield and tuber size distribution at the last three harvest dates (Table 2). Umatilla Russet was among the heavier bulking clones when harvested 132 DAP. Marketable yields for Umatilla Russet showed the earliest bulking potential at 132 DAP with 513 cwt/acre, compared to Russet Burbank and Shepody with 473 and 425 cwt/acre, respectively. The percent U.S. No. 1 yields were 87, 59, and 69 percent, respectively. Russet Burbank also had a sugar end incidence of 37.5 percent, the highest of any clone at this harvest date.

Growers can only plant varieties that have seed available and that have been accepted by processing companies for contract production. At present, seed is available for Umatilla Russet, Shepody, and Ranger Russet. When the bulking rate of Umatilla Russet, Shepody, and Ranger Russet are compared over the last three harvest dates, Umatilla Russet tended to have a yield advantage. Other clones, such as A92294-6 and A93157-6LS, were also promising (Table 2).

Tubers in the larger than 12 oz size category are too big for optimum production of frozen french fries. Because 6-10 oz tubers are considered ideal for processing, the yield of that size category was graphed over time, along with total yield and marketable yield for each potato clone (Figs. 2-14).

In previous work Shock et al. (2003) showed that a major factor limiting potato productivity in Malheur County is the failure of tubers to continue to bulk late in the growing season. In the current work, most varieties and experimental clones failed to have substantial marketable yield increases after 153 DAP (Figs. 3-5, 8-13). This lack of increase in marketable yield after 153 DAP was noted for Ranger Russet, Russet Burbank, Shepody, and Umatilla Russet (Figs. 9-12). In contrast, A92294-6 and A93157-6LS continued their upward trends in marketable yield to 174 DAP (Figs. 6 and 7), finishing with 689 and 658 cwt/acre, respectively. These clones deserve special attention in future trials and possible tests for resistance to early death through heat stress and the component pathogens of the “early die” syndrome (Fig. 14).

The average date of last frost at Malheur Experiment Station is April 29. In this trial planted on April 10, 2003, an overnight low of 32° F occurred on the night of May 19, but no frost injury was observed. Any early harvest yield advantage of early planting dates has to be weighed in relation to the risk of frost damage.

Although Shepody is widely used as an early harvest variety, it is not especially suited as an early harvest variety. Many other clones included in this trial bulked fairly early (Figs. 3-5, and 14) compared to Shepody. Of these, A90586-11 has shown resistance to late blight in addition to having good yield and processing quality. From the Western Regional Early Potato Variety Trials in Ontario over the past few years several additional new clones have shown promise for early harvest (data not shown).

References

Shock, C.C., E.P. Eldredge, and L.D. Saunders. 2003. Tuber bulking rate of processing potato clones in relation to planting date. Oregon State University Agricultural Experiment Station, Special Report 1048:152-158.

Table 1. Fertilizer applied to potato clones and varieties grown under drip irrigation, Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.

Date	NO₃	P₂O₅	K₂O	SO₄	S	Fe	Mg	Mn	Zn	Cu	B
	-----------------------------------------------lb/acre----------------------------------------------
6/19	28.5							0.36		0.23
7/1	20.0	6.0		1.3			0.5	0.25	0.25	0.25
7/17	20.0			43.0				0.25	0.25
7/19					40.0
7/28	3.2	10.0	1.1						0.09
8/5	16.0	11.4	11.4	10.0		0.57		0.28	0.23	0.28	0.01
8/14	20.0							0.25		0.20
total	107.7	27.4	12.5	54.3	40.0	0.57	0.5	1.39	0.82	0.96	0.01

Table 2. Tuber yield, grade, length-to-width ratio, specific gravity, and fry color of five potato clones and six potato varieties that grew until vine removal on August 20, September 5, or October 1. Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.

		Days						_Marketable						Fry color light
		_after		Total	U.S. No.1			_yield			_Tubers	_Length	_Specific	_reflectance			_Sugar
	planting			yield	Yield	Percent		Total		6-10oz	<4 oz	/width	_gravity	stem	bud	avg.	ends
Cultivar/clone	Hrv		DAP	-cwt/acre-			%	-------cwt/acre--------				ratio	gcm^-3	------------%-------------
A9014-2	8/20		132	496	469		98	481	146		15	1.60	1.085	57	59	58	0.0
	9/5		153	545	507		96	528	143		17	1.64	1.086	58	58	58	0.0
	10/1		174	567	539		98	553	97		14	1.71	1.082	55	57	56	1.3
A9045-7	8/20		132	514	435		89	489	184		24	1.62	1.089	45	42	43	0.0
	9/5		153	538	425		83	504	152		34	1.70	1.088	40	43	41	3.8
	10/1		174	624	513		87	586	137		38	1.68	1.086	39	42	40	5.0
A90586-11	8/20		132	483	353		80	441	183		42	1.83	1.086	48	44	46	1.3
	9/5		153	505	329		71	464	160		41	1.87	1.090	37	46	42	5.0
	10/1		174	596	363		66	557	170		39	1.84	1.090	35	44	40	12.5
A92294-6	8/20		132	535	438		89	492	268		43	2.07	1.092	55	52	54	0.0
	9/5		153	643	431		72	605	233		38	2.06	1.089	45	56	51	2.5
	10/1		174	728	556		80	689	269		39	2.08	1.089	46	56	50	1.3
A93157-6LS	8/20		132	483	423		94	451	192		32	1.81	1.085	47	39	43	13.8
	9/5		153