This was the second year of testing potato varieties grown under drip irrigation. Last year's annual report contains the data for some new, numbered lines compared to standard russet varieties, harvested either 80 or 120 days after emergence. This year the Early and Late Harvest Russet trials compared eight russeted or processing varieties to three numbered lines and one newly released fresh market variety. We included 'Shepody', an important white-skinned variety used for processing, and 'Klamath Russet', a newly-released fresh market variety. A group of six red-skinned varieties was also grown, comparing three old standard varieties to two new, numbered lines and one newly released red variety, 'Mazama'.
Water quality and scarcity issues may lead some growers to adopt drip irrigation for production of potatoes. The limited profitability of other crop options may lead some growers to produce red-skinned or specialty potatoes for fresh market. The objectives of this study were to evaluate the performance of new varieties and advanced numbered potato lines compared to standard varieties under drip irrigation, and to explore the applicability of drip irrigation to potato production in Malheur County.
Materials and Methods
The 2000 drip irrigated Early and Late Harvest Red and Russet variety trials were grown on a field of Owyhee silt loam where winter wheat was the previous crop. The wheat stubble was flailed, the field was furrow irrigated, and disked, then 100 lb P/acre and 20 lb N/acre were broadcast. On October 12, 1999, the field was ripped with Telone II injected at 22 gal/acre, and on November 16 the field was bedded on 36 inch row spacing. A soil test March 30, 2000 showed available nitrate plus ammonia nitrogen totaled 106 lb N/acre in the top 2 ft of soil, 41 ppm extractable P, 484 ppm K, organic matter 1.7 percent, and pH 6.7.
Seed of all varieties was hand cut into 2-oz seedpieces and treated with Tops MZ dust. The Early Harvest Red and Russet trials were planted April 20, and the Late Harvest Red and Russet trials were planted April 27 . Both trials had five replicates, with varieties as treatments in randomized complete block designs. Potato seed was planted using a Parma (Parma Corp., Parma, ID) two-row cup planter with the center furrowing shovel removed. Seedpiece spacing was 9 inches in the row, with rows 36 inches apart, and Thimet 20G was metered into the seed furrow at a rate of 1.7 oz/100 ft of row. Plots were two rows wide by 26.5 ft (35 seedpieces) long, with five red seedpieces separating the plots of russeted varieties and five russet seedpieces separating the plots of red varieties.
Prowl at 1 lb ai/acre plus Dual at 2 lb ai/acre, in 30 gal/acre spray mix, was applied on May 4, 2000 and incorporated with a spike-tooth bed harrow on May 10. The bed harrow had a toolbar on the back carrying large wide shovels to lift soil out of the furrows. A vee of heavy chain was dragged from the shovel shanks to move soil into the center of the bed. On the second pass with the bed harrow, in the opposite direction from the first pass, drip tube was injected 2 to 3 inches deep in the center of the level bed between the two potato rows. The drip tube was 1000 Path (Nelson Irrigation, Walla Walla, WA) 8 mil, 12-inch emitter spacing, 0.22 gal/min/100 ft flow rate.
The potatoes in both sets of trials were irrigated with one drip tube between two rows of potatoes on a raised bed. Irrigations were automated to maintain the soil water potential at -30 centibar in the root zone measured with Watermark sensors (Irrometer Corp, Riverside, CA). The sensors were positioned with the center of the sensor 8 inches deep, between potato plants in the row. All the nitrogen fertilizer was injected through the drip tape. A 100-gallon tank was used to dissolve calcium nitrate. The solution was metered into the irrigation water using a model A30-2.5 percent Dosmatic metering pump (Dosmatic USA International, Inc., Carrolltown, TX). Fertilizer was injected to supply 50 ppm NO3 in the drip system from June 2 to July 10, when additional calcium nitrate was injected to bring the total applied to 140 lb N/acre. From July 11 to August 2 fertilizer solution was injected to maintain 50 ppm NO3 in the drip system, resulting in total applied fertilizer of 180 lb N/acre. Irrigations were continued through September 19 without fertilizer injection.
Fungicide applications to prevent late blight infection included an aerial application of Bravo at a 1.5 pint/acre of June 6, and then with Dithane at 4 pint/acre on June 16. Powdered sulfur was applied at 30 lb/acre by airplane on July 11, and again on August 3, to control powdery mildew.
Early Harvest Trials
Vines were flailed in the early harvest trials on August 21, 87 days after full emergence. Early harvest red and russet potatoes were lifted August 24 with a two-row digger (John Deere, Moline, IL) that laid the tubers back onto the soil in each row. Potatoes were visually evaluated for desirable traits, such as smooth, uniformly shaped and sized, oblong (or blocky) to long, attractively russetted tubers, with shallow eyes evenly distributed. Red varieties should have a high yield of uniformly shaped, small, smooth, brightly colored tubers. Notes were also made of tuber defects such as growth cracks, knobs, curved or irregularly shaped tubers, pointed ends, stem-end decay, stolons that remained attached, folded bud ends, rough skin due to excessive russetting, drab or dull color on red varieties, pigmented eyes, or any other defect.
The drip tape was dug along with the potatoes. It fed over the two-row primary chain digger and was gathered up by hand and tied in bundles for disposal after the potatoes had been picked up. Tubers were placed into burlap sacks and hauled to a barn where they were kept under tarps until grading on August 29 and 30. A 20-tuber sample from each plot of the russet varieties was placed into refrigerated storage for processing quality tests. The storage was kept near 100 percent relative humidity and the temperature was gradually reduced to 45°F.
Late Harvest Trials
Vines were flailed off the Late Harvest Red and Russet trials on September 19, 116 days after full emergence. The potatoes were lifted on September 28 and 29 with a two-row digger that laid the tubers back onto the soil in each row. At harvest, the potatoes in each plot were visually evaluated as described above. Tubers were graded October 2 and 3 and a 20-tuber sample from each plot of the russet varieties was placed into storage. Tubers were removed from storage November 30 through December 1 and evaluated for tuber quality traits, specific gravity was measured, and 20 tubers per plot were cut lengthwise and examined for internal defects. Center slices from 20 tubers were fried for 3.5 minutes in 375°F soybean oil. Percent light reflectance was measured on the stem and bud ends of each fried slice using a model 577 Photovolt Reflectance Meter (Seradyn, Inc., Indianapolis, IN), with a green tristimulus filter, calibrated to read 0 percent light reflectance on the black standard cup and 73.6 percent light reflectance on the white porcelain standard plate.
Results and Discussion
Potatoes planted on April 20 began to emerge a few days earlier than potatoes planted on April 27, but emerged less uniformly, with some of the red varieties emerging earliest. Some of the early planted russet varieties were the slowest to emerge, so that the potatoes in all the trials had not fully emerged until May 26. The automated drip irrigation system applied 12.9 acre-inches of water to the Early Harvest variety trials, and 20.3 acre-inches to the Late Harvest variety trials.
The summer of 2000 was not intensely hot, however the heat was prolonged. The highest temperature was 102°F on August 2. During June, July, and August, there were seven days 100°F or higher, and 56 days above 90°F. Daytime high temperatures over 86°F are stressful for potato, and 70 days between June 1 and August 31 had high temperatures 86°F or above. Powdery mildew was found on the foliage of potatoes in the trial on July 6. Powdery mildew is often a problem on potatoes in Malheur County, and was widespread in 2000. The unusually hot, dry weather in June allowed powdery mildew to infect the crop, and the prolonged hot, dry weather in July and August favored its spread and made control difficult in potato and other crops. Dry weather prevented late blight from developing in 2000. Hot weather also increased evapotranspiration. The monthly total pan evaporation in 2000 measured at the U.S. Weather Bureau Class A pan at Malheur Experiment Station exceeded the 52-year average for the month of May by 14 percent, June by 21 percent, July by 14 percent, August by 25 percent, and September by 11 percent. The April through October 2000 total pan evaporation was 60.76 inches compared to the 52-year average of 52.11 inches.
Red Early and Late Harvest
The red varieties were graded into categories that reflected their usual culinary, and therefore market, uses. The total yield of tubers under 10 oz was considered the marketable yield. The under 2 oz, and 2 to 5 oz size categories can command premium prices, while tubers over 10 oz are frequently unmarketable. Harvested early, the red-skinned varieties average total yield was 422 cwt/acre, and with yields of 'Red Lasoda' at 442 cwt/acre, and 'Mazama' at 440 cwt/acre, and only the lowest yield, 'Sangre 14' at 350 cwt/acre, being significantly different in yield (Table 1). Harvested late, the average total yield was 525 cwt/acre, with no significant differences in total yield among the varieties or lines. 'Mazama' had the highest yield of tubers under 10 oz in both the Early and Late Harvest trials, and the highest proportion of U.S. No. 1 potatoes in both trials, and 'Red LaSoda' produced the highest yield of tubers over 10 oz. in both trials. A higher proportion of tubers in the smaller size categories can be controlled by closer spacing of the seedpieces in the row, or by presprouting the seed so that each seedpiece produces more stems.
Russet Early and Late Harvest
In the early harvest russet varieties, the overall average total yield was 349 cwt, with the highest yield by 'AO87277-6' at 401 cwt/acre, and the lowest yield 'Klamath Russet' at 296 cwt/acre, and 'Ranger Russet' at 300 cwt/acre (Table 2). Marketable yield includes all sizes of U.S. No. 1 grade tubers and the U.S. No. 2 grade tubers. In marketable yield for the early harvest russets, the highest was 'AO87277-6' at 380 cwt/acre, followed by 'AO92023-3' at 355 cwt/acre, and others. The early harvest russets with the highest specific gravity were 'AO87277-6', 'Shepody', 'Ranger Russet', and 'Umatilla Russet'. The lines 'AO87277-6', 'Umatilla Russet', and 'AO92007-2' had among the lightest stem-end fry color.
In the Late Harvest Russet trial, the overall average total yield was 430 cwt/acre, with the highest total yield by 'Umatilla Russet' at 537 cwt/acre, and the lowest yield by 'Klamath Russet' at 320 cwt/acre. 'Umatilla Russet' at 435 cwt/acre had among the highest marketable yield in the Late Harvest Russet trial along with 'AO92007-2', 'AO93023-3', 'AO87277-6', and 'Shepody'. In the Late Harvest Russet trial 'Russet Burbank', 'Ranger Russet', and 'Klamath Russet' produced among the lowest marketable yields. In the Late Harvest Russet trial 'AO87277-6', and 'Ranger Russet' were among the lines with the highest specific gravity. The lines 'AO87277-6', 'Umatilla Russet', 'AO92007-2', and 'Ranger Russet' were among the varieties with the lightest stem-end fry color.
Difference between Early and Late Harvests
These trials compared two matched sets of plots, grown in the same field but harvested at different times. Any differences among the variety averages for tubers harvested early or harvested late cannot be assigned a probability because the sources of variability cannot be evaluated. Some of the differences were large enough to raise questions that could be tested in future research designed to answer those specific questions.
The increase in yield of the smallest tubers, under 2 oz for reds and under 4 oz for russets, late in the growing season might represent a second set of tubers. That could have been brought on by a brief fluctuation of soil moisture when the computerized irrigation control system failed temporarily in early August, or by excessive nitrogen fertilizer, or a combination of those factors.
In comparing the early and late harvest yields of the red-skinned varieties, 'Sangre 14' increased 205 cwt/acre at the end of the season, mostly by bulking tubers larger than 10 oz. 'Mazama', on the other hand, did not increase tubers over 10 oz, suggesting there may be a genetic mechanism limiting tuber size in 'Mazama'. This would be a valuable trait in a red potato. The difference in harvest dates increased 'Mazama' total yield 69 cwt/acre, for a bulking rate of 2.48 cwt/acre/day, while 'Sangre 14' total yield difference was an increase of 205 cwt/acre, for an average bulking rate of 7.07 cwt/acre/day during the period from August 21 to September 19.
'Umatilla Russet' had the greatest increase in yield of marketable tubers between early and late harvests, 94 cwt/acre or 5.86 cwt/acre/day. The lowest bulking rate at the end of the season was that of 'Klamath Russet' at 0.83 cwt/acre/day. 'Umatilla Russet' and 'Ranger Russet' both increased in total yield late in the season, but both also suffered a slightly reduced percentage of No. 1 tubers. The late season productivity of these varieties suggests healthier vines at the end of the season. Late season vine health may be a reflection of resistance to Verticillium wilt or another pathogen that contributes to early vine death. 'Shepody' and 'Klamath Russet' both showed a decreased specific gravity later in the season. All of the late harvested russets fried darker except 'Ranger Russet'.
Table 1. Red potato varieties harvested after 87 or 116 days of vine growth: yield, grade, and differences between the harvest dates. Malheur Experiment Station, Oregon State University, Ontario, OR 2000.
|Early harvest||U.S. No. 1||U.S. No. 2|
|Total||Percent||< 10||< 2||2 to 5||5 to 10||>10||< 10||> 10|
Table 2. Russet potato varieties harvested after 87 or 116 days of vine growth: yield, grade, and differences between the harvest dates. Malheur Experiment Station, Oregon State University, Ontario, OR 2000.
|Early Harvest Variety||Total Yield||Percent No. 1||Total
|Marketable||> 12||6 to 12||4 to 6||< 4||U.S.
|cull||rot||Specific gravity||Stem end|