Clinton C. Shock, Eric P. Eldredge, and Lamont D. Saunders
Malheur Experiment Station
Oregon State University
The four varieties 'Shepody', 'Ranger Russet', 'Umatilla Russet', 'Wallowa Russet', and the six numbered clones 'AC87138-4', 'A8893-1', 'A9014-2', 'A90586-11', 'A9304-3', and 'AO96177-6' were compared at three planting dates and four harvest dates in this trial. 'Shepody' and 'Ranger' are currently grown for early harvest and processing and serve as the check varieties. 'Umatilla' and 'Wallowa Russet' are new releases from Oregon State University (OSU) that have yield, grade, and processing quality superior to 'Shepody' and 'Ranger'. The numbered clones have performed well in previous variety trials, including the Western Regional Early- harvest Trial at this location, over several years. 'A90586-11' has shown resistance to late blight in addition to having good yield and processing quality. The 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, and compare them to the varieties currently grown for early harvest for processing.
Materials and Methods
The soil was Owyhee silt loam. A soil test taken October 1, 2001, showed 13 ppm nitrate, 31 ppm extractable P, 249 ppm K, 6 ppm sulfate, 336 ppm Mg, 0.2 ppm Zn, 4 ppm Mn, 21 ppm Fe, 0.2 ppm Cu, 0.6 ppm B, organic matter 1.8 percent, and pH 8.1. Fall fertilizer containing 50 lb/acre N, 160 lb/acre P2O5, 100 lb/acre K, 40 lb/acre SO4, 190 lb/acre S, 10 lb/acre Zn, 4 lb/acre Mn, 2 lb/acre Cu, and 1 lb/acre B was applied and incorporated into the soil. The field was fumigated with Telone II at 22 gal/acre and bedded on 36-inch rows on November 11, 2001.
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 'Shepody' was donated by J.R. Simplot Co., from commercial certified seed produced in eastern Idaho. On March 28, seed for the earliest planting was cut by hand into 2-oz pieces, treated with Tops MZ Gaucho seed-treating dust, and counted into bags of 88 seed for each plot.
The experimental design was a split-block repeated measures design, with each variety randomized and replicated three times on each of three planting dates, to be sequentially sampled at four harvest dates. This was accomplished by leaving 30-ft alleys between the blocks in the field to allow turning the tractor and potato planter into and out of each block of plots. Plantings were made on April 5, April 15, and April 25. Seed of each cultivar was planted into a single row plot, with rows spaced 36 inches apart and 12-inch spacing between seed pieces in the row. Dry weather permitted planting on the planned dates spaced 10 days apart, and the field condition was excellent, with good tilth and good soil moisture. The soil temperature at the seed piece depth, 10 inches, was 50°F on the first planting date because of unusually warm weather at the end of March. On April 15 the soil temperature at 10 inches was still 50°F, and was 52°F on April 25. A two-row per bed configuration was maintained at planting by leaving off the center furrowing shovel of the two-row planter. After planting, flat-topped beds were formed with a spike-tooth bed harrow and winged shovels, dragging a 14-ft length of chain to pull soil into the bed center.
A soil test taken on March 4 showed available nitrate plus ammonia in the top 2 ft of soil totaled 93 lb/acre N, and the top foot of soil had 38 ppm extractable P, 469 ppm K, 5 ppm Mn, 27 ppm Fe, 0.4 ppm Cu, 13 ppm sulfate, 0.4 ppm B, 2.4 percent organic matter, and pH 6.9. No fertilizer was applied in spring, until fertilizer injection into the drip-irrigation system in response to petiole tests was begun.
A herbicide mixture of Prowl at 1 lb ai/acre plus Dual at 2 lb ai/acre was applied for weed control on April 29. On May 2, before any potato plants had emerged, the bed harrow with wide shovels was used to incorporate the herbicides and shank in drip tape at 3-inches depth in the top of the bed between the two potato rows. Drip tape was 5/8-inch diameter, 5-mil wall thickness, with 12-inch emitter spacing, and 0.22-gal/min/100 ft flow rate. The potatoes were irrigated so that applied water matched potato evapotranspiration. Matrix herbicide was applied at 1.25 oz/acre on May 16.
Ridomil Gold plus Bravo was applied by aerial applicator on June 4, Dithane on June 16, and Bravo Weatherstik plus Super-six flowable sulfur on July 2 to prevent foliar fungal blight diseases. Sulfur dust was applied by aerial applicator on July 23 to control mites and powdery mildew.
Petiole tests were taken on June 7, 24, July 8, 22, and August 5 and fertilizer was injected on June 17, 26, July 12, 25, and August 12 to prevent any nutrient deficiencies from developing. Total nutrients applied through the drip irrigation system were 127 lb/acre N, 13 lb/acre S, 1.37 lb/acre Zn, 0.33 lb/acre Mn, 0.34 lb/acre Cu, 1.56 lb/acre Fe, and 0.68 lb/acre B.
On June 27, the first tuber samples were dug from 5 ft of row in each plot, after digging and discarding one outside (border) plant from the end of each row. Tubers were sorted by weight, counted, and specific gravity and the length-to-width ratio were measured. On July 18, tubers from 20 ft of row were harvested from each plot, after discarding one border plant. Tubers were sorted by weight, counted in each weight category, and specific gravity, length-to-width ratio, and fry color were measured on a sample of 20 tubers from each plot. The third harvest, on August 8, followed the same procedure. For the final harvest on August 28, one plant was removed from each end of each row, the vines were flailed, and the remaining length of each row was measured.
Potatoes planted on April 5 had 50 percent emergence by May 13, those planted on April 15 had 50 percent emergence by May 22, and on April 25 had 50 percent emergence by May 29. Evaluation of tuber initiation timing and number per plant began on June 7.
Considering all the 10 varieties together, planting date was a key to adequate total yields over all harvest dates (Table 2, Fig. 1). Total marketable yields followed the same general pattern (Fig. 2). The delay in planting from April 5 to April 25 resulted in the loss of total yield and marketable yield of about 75 cwt/acre regardless of early harvest date. Yield of potatoes planted on April 15 was intermediate between those of April 5 and April 25.
Potato clones varied in their bulking rate at each planting date (Figs. 3-5). Among the potatoes tested, 'Umatilla Russet' was among heavier bulking clones at all planting and harvest dates.
Growers have the option to plant only varieties that have seed available and that have been adopted by processing companies. At present, seed is available for 'Umatilla Russet', 'Shepody', and 'Ranger Russet'. When the bulking rate of 'Umatilla Russet', 'Shepody', and 'Ranger Russet' planted April 5 were compared over all harvest dates, 'Umatilla Russet' tended to have a yield advantage (Fig. 6). Other clones were also promising (Table 1).
One of the conclusions from this trial is that an early planting date is crucial to achieve adequate yields and returns for early harvest for processing. Delay of 20 days in planting cost about 75 cwt of marketable yield, regardless of harvest date. Potatoes planted in another of our trials on April 5, 2002, were completely frost-nipped, indicating that in 2002, April 5 was about the earliest safe date to plant and avoid frost damage. The advantage of early planting dates has to be considered in relation to frost risks.
A second conclusion is that 'Shepody' and 'Ranger' are not especially suited as early harvest varieties, but are only two of several clones that could be planted. Other clones included in this trial also bulked fairly early (Figs. 3-5). From the 2002 Western Regional Early Potato Variety trial in Ontario, several other new clones demonstrated promise (data not shown).
The trial was planted with 12-inch seed spacing to obtain early production of marketable tubers. The choice of 12-inch seed spacing appears to have been a disadvantage, since many of the tubers ended up in the >12 oz size category by mid-July (Tables 1 and 2). Tuber size distribution and total marketable yields would have probably been better with 9-inch spacing at planting. All of the clones tested in the 2002 trial had been selected in previous years based on performance at 9-inch spacing.
Table 1. Tuber size distribution, yield, length-to-width ratio, specific gravity, and fry color of 10 potato varieties planted on April 5 and harvested on August 29, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
|Variety||<2 oz||2-4 oz||4-6 oz||6-8 oz||8-10 oz||10-12 oz||>12 oz||Total yield||Marketable yield||Length to width||Specific gravity||Stem end||Bud end||Average fry color|
||---------------------------------cwt/acre-----------------------------------||ratio||gcm-3||light reflectance %|
Table 2. Average tuber size distribution, yield, length-to-width ratio, specific gravity, and fry color of 10 potato varieties planted on three dates and harvested on four dates, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
|Planting||Harvest||<2 oz||2-4 oz||4-6 oz||6-8 oz||8-10 oz||10-12 oz||>12 oz||Total yield||Marketable yield||Length to width||Specific gravity||Stem end||Bud end||Average fry color|
|date||--------------------------------cwt/acre---------------------------------||ratio||gcm-3||light reflectance %|
Figure 1. Total tuber bulking over time for three planting dates averaged over 10 potato clones, Oregon State University, Malheur Experiment Station, Ontario, OR, 2002.
Figure 2. Marketable tuber development over time for three planting dates averaged over 10 potato clones, Oregon State University, Malheur Experiment Station, Ontario, OR, 2002.
Figure 3. Total tuber bulking over time for 10 potato clones planted on April 5, 2002, Oregon State University, Malheur Experiment Station, Ontario, OR.
Figure 4. Total tuber bulking over time for 10 potato clones planted on April 15, 2002, Oregon State University, Malheur Experiment Station, Ontario, OR.
Figure 5. Total tuber bulking over time for 10 potato clones planted on April 25, 2002, Oregon State University, Malheur Experiment Station, Ontario, OR.
Figure 6. Marketable tuber yield for four harvest dates for 'Shepody', 'Ranger Russet', and 'Umatilla Russet' planted on April 5, 2002, Oregon State University, Malheur Experiment Station, Ontario, OR.