Nitrogen fertilization of irrigated Russet potatoes in southcentral Alaska

Allagash Russet, BelRus, Frontier Russet, HiLite Russet, Russet Norkotah and Russet Burbank were evaluated with preplant N fertilizer levels of 0, 67, 134, 201, and 201 kg N/ha in a split application on a Knik silt loam in 1990 and 1991 near Palmer, Alaska. BelRus and Russet Norkotah yielded less marketable tubers than the other cultivars and Russet Burbank performed well under warm, dry 1990 conditions and poorly when conditions were cool and wet (1991). Allagash, HiLite and Frontier Russets were consistent producers with marketable tuber yields averaging 35.4, 32.3, and 32.2 t/ha, respectively. Marketable tuber yield was maximized with approximately 175 kg total N/ha (residual soil plus applied) and approached 43 t/ha in 1990. Splitting the N application had no significant effect on tuber yield. Newly released russets appear promising for commercial Alaska producers.     

Response of Nooksack potatoes to nitrogen fertilizer

The Nooksack cultivar because of differing characteristics may have different responses to grower management practices developed principally for Russet Burbank. This study was conducted to determine the effects of nitrogen on yield, grade, and specific gravity of the Nooksack cultivar. In irrigated field experiments, N fertilizer was sprinkler-applied daily on Quincy sand soil. In other experiments, on a Warden silt loam soil all N was broadcast and incorporated before planting. Fertilization rate did not significantly affect tuber grade or specific gravity. Short term shifts in N supply did not cause tuber deformities and poor grades as they commonly do with Russet Burbank. Nooksack, while responsive, did not have a strong positive response to N fertilization. Tuber yields were depressed at fertilizer plus residual N levels above 200 kg/ha on Warden silt loam and above 300 kg/ha on Quincy sand. This difference was because of variation in NO₃ leaching and soil N mineralization and was reflected in calculation of optimum N rates. Nooksack may require less N fertilization than Russet Burbank partially because of the strong dormancy of Nooksack tubers that retards emergence and shortens growing season. Management to promote more rapid dormancy break and lower N nutrition during tuber initiation could result in earlier establishment, earlier tuber bulking, and greater yields of Nooksacks.     

Nitrogen fertilization and irrigation affects tuber characteristics of two potato cultivars

Nitrogen fertilization, irrigation, and cultivars affect tuber characteristics such as tuber size, specific gravity, and N concentration. Few studies, however, have investigated the interaction of irrigation and N fertilization on the tuber characteristics of potato cultivars, particularly in Atlantic Canada. The objective of this on-farm study, conducted at four sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and six rates of N fertilization (0-250 kg N ha^-1) on the number of tubers per plant, the average fresh tuber weight, tuber N concentration, nitrate (NO₃-N) concentration, and specific gravity of the cultivars Shepody and Russet Burbank. Nitrogen fertilization increased the average fresh tuber weight, tuber N and N0₃-N concentrations, and decreased specific gravity. Effects of increasing N fertilization on tuber characteristics were often more pronounced for Shepody than for Russet Burbank, and for irrigated than for non-irrigated conditions. Shepody had greater average fresh tuber weight and tuber N concentration, lower specific gravity, and fewer tubers per plant than Russet Burbank. Supplemental irrigation increased the average fresh tuber weight and the number of tubers per plant, but it had a limited effect on specific gravity and tuber N and NO₃-N concentrations. Tuber NO₃-N con centration and specific gravity were strongly related to tuber N concentration, which in turn depended primarily on N fertilization. Incidents of lowest specific gravity and highest NO₃-N concentration occurred with a relative yield close to or equal to 1.0. We conclude that the risks of low specific gravity and high tuber NO₃-N concentration are greater when fertilization exceeds the N requirements to reach maximum tuber yield.     

Response of four potato cultivars to rate and timing of nitrogen fertilizer

The release of three new potato (Solarium tuberosum L.) cultivars, Bannock Russet, Gem Russet, and Summit Russet, with unique plant growth characteristics, necessitates the development of appropriate N fertilizer recommendations. These three new cultivars, along with the standard cultivar, Russet Burbank, were treated with four N rates (0, 100, 200, and 300 kg N ha^?1) using two different application timing procedures (“early,” with two-thirds N applied preplant, and “late,” with one-third applied preplant). Measurements included total and U.S. No. 1 yields, petiole NO₃-N concentrations, and net returns derived from economic analysis using a processing-based contract. Each of the four cultivars showed a unique response to N application treatments. Bannock Russet achieved maximum yield and net returns with relatively small amounts of N fertilizer. It also showed no response to N application timing and had moderate NO₃-N sufficiency concentrations early in the season, that decreased markedly late in the season. Gem Russet N requirement for maximum yield was similar to that of Russet Burbank, but required a higher amount of N for maximum net returns. Gem Russet also showed no response to application timing and had NO₃-N sufficiency concentrations similar to or slightly higher than those of Russet Burbank. Summit Russet showed a strong trend for improved N use-efficiency when most of the N was applied early. On the other hand, analysis of net returns revealed a trend for greater profitability for Summit Russet when the majority of N was applied during tuber bulking. Petiole NO₃-N sufficiency concentrations for Summit Russet were generally higher than those for the other three cultivars. In comparison with some earlier studies with Russet Burbank, this research suggested lower optimal N rates and petiole NO₃-N sufficiency concentrations.     

Critical petiole nitrate concentration of two processing potato cultivars in Eastern Canada

Plant-based diagnostic methods of nitrogen (N) nutrition such as petiole nitrate (NO₃-N) concentration can be used to improve the efficiency of N utilization, and hence decrease the risks of N losses to the environment. Our first objective was to determine the effect of N fertilization and supplemental irrigation on the petiole NO₃-N concentration during tuber growth of two potato cultivars, Russet Burbank and Shepody, widely grown for processing in Eastern Canada. Our second objective was to establish the critical petiole NO₃-N concentration using the relationship between petiole NO₃-N concentration and the N nutrition index (NNI), an index based on the N concentration of shoots and tubers. This on-farm study was conducted at two sites in each of three years, 1995 to 1997. The N fertilization rates ranged from 0 to 250 kg N ha^?1 with three rates in 1995, six rates in 1996, and four rates in 1997. The NO₃-N concentration of petioles from the most recently mature leaves was measured on three sampling dates in 1995 and four sampling dates in 1996 and 1997. The petiole NO₃-N concentration generally decreased with time. At all sites and on all sampling dates, the petiole NO₃-N concentration increased with increasing N fertilization and was significantly greater for Shepody than for Russet Burbank. Irrigation had no consistent effect on petiole NO₃-N concentration. Petiole NO₃-N concentration was related to NNI (0.29<R²<0.62). Critical petiole NO₃-N concentrations required to reach a NNI of 1.0, indicating a situation where N is not limiting growth, were greater for Shepody than for Russet Burbank, and they decreased with time. Critical petiole NO₃-N concentrations (Y) expressed as a function of the number of days after planting (X) are Y = 4.80 - 0.055X for Russet Burbank and Y = 5.03 - 0.054X for Shepody.     

Russet Burbank yield response to sprinkler-applied nitrogen fertilizer

Yield response curves were developed for potatoes (Solanum tuberosum cv. Russet Burbank) with sprinkler-applied N fertilizer on a high-frequency schedule. The potatoes were grown on a Quincy sand to loamy sand (mixed, mesic, Xeric Torripsamments) typical of sandy-textured soils of the center-pivot irrigated areas of the Columbia River Basin of Oregon and Washington. These soils require daily irrigation at peak evapotranspiration because of low water-holding capacity. Yields were measured for total quantities of N, ranging from 100 to 665 kg N/ha, applied in small frequent increments as a urea-NH₄NO₃ solution. Maximum tuber yields ranged from 67 to 85 Mg/ha in 6 experiments over a period of 6 years. Economically optimum yields were obtained at fertilizer rates between 300 and 400 kg N/ha depending on cost-price ratio of N fertilizer and potatoes. Fertilization in this range should optimize tuber yield and quality with fertilizer N efficiency and economic return on fertilizer investment.     

Tuber growth and biomass partitioning of two potato cultivars grown under different n fertilization rates with and without irrigation

Nitrogen and water deficiencies are known to affect potato yield, but much less is known of their effect on tuber growth and biomass partitioning. The objective of this on-farm study conducted at two sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and N fertilization rates on tuber growth and biomass partitioning of the cultivars Shepody and Russet Burbank. The N fertilization rates were 0,100, and 250 kg N ha^-1in 1995, and 0, 50,100, and 250 kg N ha_?1 in 1996 and 1997. The highest bulking rate observed in our study (7.3 g fresh tubers m^-2 °C^-1) can be considered near the potential bulking rate in New Brunswick. The water deficit in the absence of supplemental irrigation reduced this potential bulking rate by as much as 40%, but this reduction was much less at five of six sites and negligible at two of six sites. Nitrogen deficiency reduced the bulking rate at two of six sites. This negative effect of N deficiency on bulking rate was greater with irrigation than without irrigation at two of six sites; the tuber bulking rate with irrigation was reduced by as much as 50% with no N applied at one site. Shepody had a greater bulking rate than Russet Burbank. The tuber bulking of Russet Burbank, however, started earlier and lasted longer than that of Shepody. Water and N deficiencies increased biomass partitioning to tubers and large roots. Shepody partitioned a greater proportion of its biomass to large roots and had a greater root biomass than Russet Burbank. Our results demonstrate the ability of potatoes to modify biomass partitioning when grown under water and/or N stresses. As a result of this compensation, the reduction in tuber yield due to limited N and water stresses is minimized.     

Impact of early-season water deficits on Russet Burbank plant development,tuber yield and quality

Russet Burbank potatoes grown on Owyhee silt loam were subjected to early-season moisture stress by delaying initiation of furrow irrigation up to seven weeks after planting. A range of water stress treatments from 4 to 7 weeks after planting resulted in reduced plant size, tuber number and total tuber weight per plant 8 1/2 weeks after planting. Early-season water stress resulting from delayed irrigation onset was associated with improved tuber quality at harvest. Plants water stressed before tuber initiation had fewer tubers with dark stem-end fry colors, reduced percentage of US No. 2 potatoes, and increased percentage and size of US No. 1 potatoes. Increasing duration of soil water potential below -60 kPa early in the season was associated with declining total yield in 1985 but not in 1986. To obtain optimum yield and processing quality, the first irrigation should be no sooner than full plant emergence.     

Yield,market quality and petiole nitrate concentration of non-irrigated Russet Burbank and Shepody potatoes in response to sidedressed nitrogen

Russet Burbank and Shepody potatoes were grown with the following four nitrogen treatments: 1) 90 kg ha^?1 at planting; 2) 180 kg ha^?1 at planting; 3) 90 kg ha^?1 at planting followed by an additional 90 kg ha^?1 side-dressed after tuber initiation; or 4) 90 kg ha^?1 at planting followed by an additional 45 kg ha^?1 sidedressing. When compared to the 90 kg ha^?1 at-planting treatment, petiole NO₃-N concentrations increased rapidly after sidedressing and were relatively constant through mid-season. Sidedressed N significantly increased total yields relative to the 90 kg N ha^?1 at-planting treatment by an average of 5.0 t ha^?1 in three of nine experiments. Three of the experiments, where yields did not significantly increase, were on sites which were not expected to respond to supplemental N based on petiole NO₃-N testing. A red clover green manure crop was the previous crop for two of these experimental sites. Petiole NO₃-N testing criteria were only partially effective in detecting sites where response to sidedressed N occurred. When compared to a single application of 180 kg N ha^?1 at planting, split application of 90 kg N ha^?1 at planting followed by a 90 kg N ha^?1 sidedressing significantly reduced total yields in one of nine experiments and did not affect yields in the remaining eight experiments. Tuber uniformity was improved in three of nine experiments by the split-N treatment. Specific gravity was not significantly affected. Use of 45 kg N ha^?1 at side-dressing resulted in similar yield as the 90 kg N ha^?1 sidedressing, although yield of large-sized tubers was often decreased with the lower N rate. Use of reduced at-planting N rates followed by sidedressed N does not appear to increase yields of non-irrigated Russet Burbank and Shepody potatoes when compared to the at-planting N rates that are currently recommended. This management approach can maintain yields at levels comparable to at-planting N programs and does provide an opportunity to reduce N application rates on sites where soil N reserves and soil amendments may make a substantial N contribution to the potato crop. Side-dressed N application can frequently improve yields and tuber size when potatoes have been underfertilized at planting; however, some inconsistency in response can be expected in regions that rely on unpredictable natural rainfall.     

Evaluation of on-farm irrigation scheduling methods for potatoes

The neutron probe, infrared thermometry and crop water stress index (CWSI), and a computer-assisted irrigation scheduling method were evaluated in terms of their effect on tuber yield, tuber quality, and water use. The experiment was conducted during 1990 and 1991 near Othello, central Washington, using Russet Burbank potatoes grown in a silt loam soil. Irrigation treatments did not commence until after tuber initiation. In general, no differences in total number of tubers and total tuber yield resulted from the different scheduling methods. However, the canopy temperature method showed reduction in the yield of number one tubers in 1990. The least total irrigation water was applied during the growing season with the neutron probe method. Using CWSI values above 0.5 to 1.0 (scale 0 to 10) for two consecutive days as a threshold to schedule irrigations appeared to be adequate for potatoes grown in silt loam soils. However, shortcomings of infrared thermometry suggested that this method may not be practical for scheduling irrigation of potatoes.     

Interactive effects of nitrogen and phosphorus on verticillium wilt of Russet Burbank potato

A three-year field study was conducted during 1984–1986 to determine the interactive effects of nitrogen and phosphorus fertilization on Verticillium wilt, and yield and quality of continuously-cropped Russet Burbank potato. The experiment was conducted on a calcareous, silt loam soil with low initial levels of NO₃-N (0.9 mg/kg), P (3.5 mg/kg), andVerticillium dahliae (9 cfu/g of soil). The experimental design consisted of a factorial combination of three N treatments (unfertilized check, preplant N or split N) and three P treatments (0,120, or 240 kg P/ha) applied to the same plots during the three-year study. Nitrogen was applied at 0 or 300 kg N/ha in 1984 and 0 or 240 kg N/ha in 1985 and 1986. By the spring of 1986, soil P concentrations for the 0,120, and 240 kg P/ha treatments had increased to 7, 25, and 50 mg/kg and no additional P was applied. In addition to suppressing Verticillium wilt by as much as 95%, N & P treatments also reduced the rate of increase of soilborne inoculum ofV. dahliae. After one season of cropping, the N treatment providing the most efficient N fertilization (300 kg N/ha, split-application) resulted in significantly (p=0.01) lowerV. dahliae counts in soil than the other N treatments. After two seasons of continuous cropping, applying 120 to 240 kg P/ha produced lower populations ofV. dahliae in soil compared to the treatment with no added P. Generally, as N and P treatments approached the highest levels, both wilt incidence andV. dahliae colonization values were reduced. There was a progressive reduction in total yield in nearly all treatments during each year of continuous cropping. Reduction of yield and increased Verticillium wilt incidence was generally greater with N or P deficient plants than with optimally fertilized plants. The highest total and U.S. No. 1 yields and least Verticillium wilt were obtained each year by applying split N and 240 kg P/ha. Results show that optimal N and P can minimize both Verticillium wilt and yield losses that normally occur with intensive potato cropping.     

Differential ozone susceptibility of Centennial Russet and White Rose potato as demonstrated by fumigation and antioxidant treatments

Because quantitative field estimates of potato (Solarium tuberosum L.) yield losses attributable to ozone (O₃) air pollution damage in California need to be assessed, the antioxidant compound N-[-2-(2-oxo-l-imidazolidiny l)ethyl]-N′-phenylurea (EDU or DPX-4891) was evaluated for suitability in estimating these yield losses and in differentiating O₃-susceptible from O₃-resistant cultivars. Differential susceptibility of two cultivars, ‘Centennial Russet’ (O₃sensitive) and ‘White Rose’ (O₃-resistant), to O₃ was confirmed in greenhouse experiments. Five weekly 5-hour treatments with 25 parts per hundred million O₃ reduced tuber yield of Centennial Russet by 32% but did not reduce the yield of White Rose. In the absence of O₃ under greenhouse conditions, EDU had no observable effect on shoot dry weight, tuber number, or tuber yield of either cultivar, suggesting that EDU does not materially affect plant growth in the absence of O₃ at the treatment levels used and under the conditions herein. In field experiments conducted at the University of California at Riverside (UCR) and in commercial fields of Kern County (KC), untreated Centennial Russet and White Rose plants produced total tuber yields of 174 and 512 q/ha, respectively at UCR and 268 and 498 q/ha, respectively, at KC. At UCR, EDU applied at the highest rate—17.8 kg/ha—increased marketable and total tuber yields of Centennial Russet by 208 and 188 q/ha, respectively, and increased specific gravity by 0.013. White Rose was not affected by EDU. Averaged over four KC experiments, EDU application at 8.9 kg/ha increased Centennial Russet marketable and total tuber yields by 40 (from 214) and 45 (from 268) q/ha, respectively, whereas White Rose was not affected and averaged 398 (marketable) and 491 (total) q/ha.     

Plant nutrient uptake and potato yield response to banded and broadcast nitrogen

The response of potato plants to banding and broadcasting of N was evaluated under sprinkler irrigation utilizing well water containing 20 to 24 ppm NO₃-N. A potato crop was grown for three consecutive years on a Wasco sandy loam soil at rates of 67, 134, 202, and 269 kg N/ha, as (NH₄)₂SO₄. At each rate of N, 58 kg P/ha as superphosphate, and 112 kg K/ha as K₂SO₄, were included. Differences in PO₄-P or K concentrations in petiole tissue were minimal with no consistant differences in NO₃-N concentration whether N was banded or broadcast. With each increment of N the NO₃-N concentration increased. Total or U.S. No. 1 yields of potatoes were not consistently different whether N was banded or broadcast. Total yields increased when N was increased from 67 to 202 kg/ha. Neither yield of U.S. No. 1 grade or dry matter content of potatoes was improved when N was increased above 134 kg/ha.     

Fertilization of Russet Burbank in short-season environment

A three-year investigation determined effects of N, P, K, and S rates on tuber yield and quality, economic return, and plant nutrient status of Russet Burbank grown on mineral soils in the Klamath Basin of Oregon. Yield responses were consistent over years. The highest yields and economic returns were achieved with the combination of 202 kg N, 29 kg P, 56 kg K, and 22 kg S ha^-1. Petiole NO₃-N concentrations were below published critical levels at the optimal N fertilizer rate of 202 kg N ha-1. Yield and economic return responses to increasing N rates were positive but small. The highest yield occurred at the lowest P rate (29 kg ha^-1). Tuber yield, grade, or quality did not respond to K fertilization. Findings suggest that nitrogen fertilizer management based on petiole analysis may require modifications for short growing-season environments.     

Critical Nitrogen Curve and Nitrogen Nutrition Index for Potato in Eastern Canada

Plant diagnostic methods of N deficiency should be based on the definition of a critical N concentration, that is the minimal N concentration required to achieve maximum growth. The critical N concentration (N_c) of potato was determined from six on-farm field trials in which two cultivars (Russet Burbank and Shepody) were grown under three or four N rates with and without irrigation. Dry matter yield and N concentration of shoots and tubers were determined approximately weekly during the growing season. The N_c was determined by selecting data points for which the highest total biomass comprised of shoots and tubers was obtained, and by expressing N concentration (N) as a function of total biomass (W). The N nutrition index (NNI), calculated as the ratio between measured N concentration and predicted N_c during the growing season, was then related to the relative yield measured at harvest. Under non-limiting water conditions, the allometric relationship between N_c and total biomass for Russet Burbank (N_c = 4.57W^-0.42) was different from that of Shepody (N_c = 5.04W^-0.42), indicating that Shepody had a greater N concentration than Russet Burbank. The N concentration of Shepody was also greater than that of Russet Burbank under limiting water conditions. These results suggest that there is intra-specific variability in potato for the relationship between N concentration and biomass. The NNI ranged from 0.50 to 1.4. The relationship between relative yield and NNI expressed by a quadratic function accounted for a greater proportion of the variability with irrigation (71% for Russet Burbank and 82% for Shepody) than without irrigation (65% for Russet Burbank and 32% for Shepody). Our results suggest that the NNI could be a reliable indicator of the level of N stress during the growing season, particularly under non-deficient water conditions.     

Russet Legend: A full season long Russet for processing and fresh market use

Russet Legend, a moderately late maturing variety especially suitable for frozen French fry processing but also acceptable for tablestock use (boiling, and baking), was jointly released by the Agricultural Experiment Stations of Oregon, Colorado, Idaho, and Washington, and the U.S. Department of Agriculture in 1998. Russet Legend was evaluated in irrigated trials in Oregon from 1988 to 1997, and in western regional trials from 1990 to 1992. Total yields were similar to those of Russet Burbank, but Russet Legend produced higher marketable yields. In three years of regional trials at up to 13 locations in seven western states, Russet Legend averaged 47.3 Mg/ha marketable yield compared with 36.5 Mg/ha for Russet Burbank and 33.6 Mg/ha for Russet Norkotah. Russet Legend has consistently achieved lighter fry color and higher specific gravity than Russet Burbank. Russet Legend is less susceptible toVerticillium wilt than Russet Burbank or Russet Norkotah. It is susceptible to PLRV and net necrosis, and expresses PVY foliar symptoms clearly. Russet Legend is less susceptible to tuber infection and decay caused byPhytophthora infestans than Ranger Russet and Russet Norkotah. Russet Legend is less susceptible to hollow heart, brown center, growth cracks, and sugar ends than Russet Burbank     

The joint action of nitrogen and nematicides onPratylenchus penetrans and potato yield

The joint action of nitrogen fertilizer and nematicides onPratylenchus penetrons and yield was investigated using three potato varieties (Superior, Onaway and Russet Burbank), three rates of nitrogen (84, 168 and 336 kg/ha), five edaphic pesticides (disulfoton, aldicarb, 1,3-D + MIC, carbofuran and thiofanox), and an insecticide spray to minimize the role of foliar feeding insects In 1977, disulfoton, aldicarb, and disulfoton plus 1,3-D + MIC significantly increased the yield of Superior at all nitrogen rates. The yield increases ranged from 37–56% for Superior, 15–35% for Onaway and 13–27% for Russet Burbank. Nitrogen had no detectable influence on yield. Population densities ofP. penetrans were significantly reduced by disulfoton plus 1,3-D + MIC and by aldicarb. Superior was most susceptible toP. penetrans, Onaway intermediate, and Russet Burbank moderately tolerant. Neither the potato variety or nitrogen significantly influenced the population densities ofP. penetrans In 1978 aldicarb, 1,3-D + MIC and thiofanox significantly increased yields of Superior at all nitrogen rates. Nitrogen also significantly increased yields, but only where aldicarb and 1,3-D + MIC were applied. Total yield was increased 12–14% and 17–23% by 1,3-D + MIC and aldicarb at 168 and 336 kg N/ha, respectively. Aldicarb, 1,3-D + MIC, and thiofanox appeared to increase tuber set, while nitrogen increased tuber size. Although all of the nematicides provided some control ofP. penetrans, aldicarb had the highest degree of efficacy and gave excellent season-long control     

Effect of rate and time of fertilization on nitrogen and yield of Russet Burbank potatoes under center pivot irrigation

Applying less N on Russet Burbank potatoes (Solanum tuberosum L.) at planting time may reduce the potential loss of N from sandy soil by wind erosion and leaching early in the season. The objective of this study was to evaluate the effect of rate and time of N fertilization on potato production. Potatoes were grown in outdoor pot cultures with N rates of 75,150 and 300 ppm and in field plots with N rates from 112 to 448 kg N/ha applied in single and split applications. The results from pot cultures harvested after one month’s growth showed that yield of tops increased and tuber yield decreased as applied N at planting increased from 75 ppm to 150 or 300 ppm. Field results showed that the yield of potatoes was as high or higher when N applications were split between planting and when plants were 15 to 20 cm tall (early tuberization) as with the same amount of N applied at planting. Generally 112 kg N/ha at planting time was sufficient when additional N was applied after emergence. Split application of N resulted in more second growth on tubers than when all of the N was applied at planting.     

Effects of moisture stress and nitrogen fertilization on tuber nitrate-nitrogen content

Moisture stress in potato plants results in a significant increase in tuber NO_3?N levels. Research plots with three irrigation treatments and four nitrogen fertilizer rates (0, 100, 200, and 500 lb N/A) (0, 112, 224, and 560 kg N/ha) were established to test the influence of soil moisture and nitrogen rate on tuber NO_3?N content. Data from these plots showed that regardless of nitrogen rate, potato tubers from plants subjected to moisture stress had NO_3?N levels approximately twice as high as tubers from plants under optimum or excessive irrigation. With low nitrogen fertilizer rates, tuber NO_3?N levels were 78 to 80 ppm under optimum and excessive irrigation treatments as compared to 144 ppm under the deficient irrigation treatment. With excessive nitrogen fertilizer rates, tuber NO_3?N levels were 151 to 154 ppm under optimum and excessive irrigation treatments compared to 370 ppm under deficient irrigation. Correlation between tuber NO_3?N and petiole NO_3?N levels suggest that moisture stressed plants have a different relationship between tuber and petiole than plants under proper to high soil moisture conditions.     

The effect of timed water stress on quality,total solids and reducing sugar content of potatoes

Potato (Solanum tuberosum L.) solids and reducing sugars were examined before, just after, and two weeks after transient water stress to gain an understanding of tuber changes that occur directly associated with water stress. Russet Burbank and A082260-8 potatoes were grown on Owyhee silt loam at the Malheur Experiment Station, Ontario, Oregon. Potatoes were subjected to a single episode of transient water stress by omitting furrow irrigation in either late June, July, or in early August of 1988 and 1989 to examine variety differences in the short term effects of water stress on changes in solids and reducing sugars in tuber stem ends. Irrigation was managed to maintain soil water potential above -65 kPa at 20 cm depth during tuber initiation through bulking except during transient stress when the soil water potential reached -82 to -110 kPa. Tuber samples were taken from plots and minimally stressed check treatments before stress, at the peak of stress, two weeks after the transient stress period, and after harvest. Tubers were sectioned longitudinally and the percent solids and reducing sugars were determined for samples from the tuber stem end, center, and apical end. Longitudinal tuber strips were fried after harvest to determine fry color. Tuber stem-end fry color did not darken in A082260-8 potatoes subjected to water stress. The line A082260-8 had higher stem-end solids and lower stem-end reducing sugars than Russet Burbank. Neither variety responded to transient water stress or recovery from transient stress with an immediate increase in reducing sugars in any tuber part. Reducing sugars were elevated in harvested tubers, particularly in the stem-ends of Russet Burbank potatoes subjected to water stress. Increases in tuber reducing sugars related to transient water stress were not found during the stress period or immediately after stress, but were present in harvested tubers.