Impact of Deficit Irrigation on Tuber Yield and Quality of Potato
Transcription
Impact of Deficit Irrigation on Tuber Yield and Quality of Potato
This article was downloaded by: [Professor A. K. Alva] On: 17 October 2012, At: 09:30 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Crop Improvement Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wcim20 Impact of Deficit Irrigation on Tuber Yield and Quality of Potato Cultivars a b A. K. Alva , A. D. Moore & H. P. Collins a a USDA-ARS, Vegetable and Forage Crops Research Unit, Prosser, Washington, USA b University of Idaho, Twin Falls Research and Extension Center, Evergreen Building, Twin Falls, Idaho, USA Version of record first published: 01 Mar 2012. To cite this article: A. K. Alva, A. D. Moore & H. P. Collins (2012): Impact of Deficit Irrigation on Tuber Yield and Quality of Potato Cultivars, Journal of Crop Improvement, 26:2, 211-227 To link to this article: http://dx.doi.org/10.1080/15427528.2011.626891 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Journal of Crop Improvement, 26:211–227, 2012 ISSN: 1542-7528 print/1542-7536 online DOI: 10.1080/15427528.2011.626891 Impact of Deficit Irrigation on Tuber Yield and Quality of Potato Cultivars A. K. ALVA1 , A. D. MOORE2 , and H. P. COLLINS1 Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 2 1 USDA-ARS, Vegetable and Forage Crops Research Unit, Prosser, Washington, USA University of Idaho, Twin Falls Research and Extension Center, Evergreen Building, Twin Falls, Idaho, USA Potato ( Solanum tuberosum L.) tuber yield and quality are impacted by irrigation and nitrogen (N) management. This study was conducted in the Pacific Northwest (PNW) region of United States to evaluate the effects of deficit irrigation (DI) and rates of pre-plant and in-season N applications on Ranger Russet and Umatilla Russet cultivars. In 2004, with Ranger Russet only, DI with 20% lower total irrigation for the entire growing period resulted in 28% tuber yield reduction compared to that of plants irrigated to replenishment full evapotranspiration (ET), i.e., full irrigation (FI). A subsequent study in 2006 and 2007 with DI (14% to 17% deficit) resulted in tuber yield reduction of 7% to 10% in both cultivars compared to full ET irrigation. Yield reduction in DI was generally attributed to reduction in large weight tubers, >0.227 kg/tuber, in both cultivars across three years. Petiole NO3 -N concentrations were greater in plants grown under DI as compared to those of plants in full ET irrigation across all years and cultivars, particularly during tuber maturation stage. This is an important consideration as increased N availability during the late growing season adversely affects tuber quality. Petiole NO3 -N concentrations increased with increased in-season N rates. Received 25 July 2011; accepted 21 September 2011. This article is not subject to US copyright law. This study was made possible by the generous support of AgriNorthwest Company, Kennewick, Wash., by providing: (i) field site, water, field equipment, and major tillage operations support during this project and (ii) petiole analyses support (Martin Moore). Grateful appreciation is also extended to Bill Boge, Marc Seymour, and several field helpers for their contributions to this experiment and preparation of this manuscript. Address correspondence to A. K. Alva at USDA-ARS, Vegetable and Forage Crops Research Unit, 24106 N. Bunn Rd., Prosser, WA 99350-8694 USA. E-mail: ashok.alva@ars. usda.gov 211 Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 212 A. K. Alva et al. In 2007, 112 kg·ha−1 in-season N resulted in petiole NO3 -N concentrations below desirable concentrations across most of the growing season in both cultivars. This, in turn, contributed to a significant reduction in tuber yield as compared to the 224 kg·ha−1 in-season N rate. Continuous DI with 14% to 20% reduction in water as compared to irrigation to replenish full ET, begun three to four weeks after seedling emergence, had significant negative effects on tuber yields of both cultivars in high-production irrigated growing conditions. Application of N up to 112 kg ha−1 as pre-plant soil applied plus 224 kg ha−1 of in-season fertigation in five applications at two-week intervals beginning four weeks after seedling emergence appears to be adequate to support high yields of high-quality tubers. KEYWORDS Solanum tuberosum, evapotranspiration, nitrogen management, nitrate leaching, petiole nutrients, harvest index, soil-water balance INTRODUCTION Water and nitrogen (N) are important inputs influencing potato (Solanum tuberosum L.) yield, quality, and net returns (Alva 2008; Shock, Pereira, & Eldredge 2007; Westermann & Kleinkopf 1985). The response to the above inputs can depend on the cultivar grown and other factors within a production system (Kleinkopf 1979). Water stress, even for a short period, often has a severe impact on potato tuber yield and quality (Eldredge, Shock, & Stieber 1992; Eldredge et al. 1996; Lynch et al. 1995; Lynch & Tai 1989; Shock et al. 1992, 1993; Shock, Feibert, & Saunders 1998, 2003) due, in part, to the shallow root system of the crop (Fulton 1970). Inadequate water availability results in loss of yield, grade, internal quality, and inefficient use of other production inputs (Shock, Pereira, & Eldredge 2007). Negative effects of deficit irrigation are particularly serious during mid- to late-season tuber bulking (Miller & Martin 1987). Ojala, Stark, and Kleinkopf (1990) determined that total and marketable yields declined with increasing soil moisture stress in the Russet Burbank cultivar. The tubers graded as U.S. No. 1 were particularly sensitive to deficit irrigation during tuber initiation. Water stress during tuber bulking influenced total tuber yield. When there was a depletion of available soil water content due to irrigation at 60%, there was a decrease in total as well as marketable tubers (total less culls and knobs) in Russet Burbank cultivar tuber yields up to 11% compared to those irrigated at 30% depletion of available soil water content (Waddell et al. 1999). The savings in irrigation water averaged across two years was close to 20% with irrigations at 60% depletion of the available soil water as compared to that with 30% Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Impact of Deficit Irrigation on Potato 213 depletion. Shock, Feibert, and Saunders (1998, 2003) evaluated six potato cultivars at deficit irrigations of 327 to 589 mm total water applied per growing season over three years. They reported that only the Russet Legend cultivar showed no significant difference in total or U.S. No. 1 tuber yield. The Russet Burbank, Shepody, Frontier Russet, Ranger Russet, and Umatilla Russet cultivars demonstrated an increase in U.S. No. 1 tuber yield as the amount of water applied increased. Effects of water stress are dependent on stage of plant growth (Wright & Stark 1990; Shock et al. 1993). Tuber initiation and bulking stages are the most sensitive to water stress as compared to the vegetative stage. It is important to conduct evaluations on the influence of DI at various growth stages in different production systems. This would be an enormous undertaking to sort out the growth stage specific effects of DI on potato production and quality. Potato is an important crop in the U.S. Pacific Northwest (PNW), i.e., the states of Washington, Idaho, and Oregon, which account for about $1.5 billion in farm gate value with a total production of 10.7 million metric tonnes (55% of U.S. total production) of tubers on 208,210 ha (National Potato Council 2006). Within this region, the Columbia Basin production area in eastern Washington is one of the most productive areas for highquality processing potatoes. Tuber yields in this region range from 60 to 80 Mg·ha−1 . The climate is characterized by long, hot, dry days followed by cool nights. The annual precipitation in this region is about 150 mm, with much of the precipitation in winter months. Irrigation is critical for economical production of most crops, including potato. The current recommendation for potato irrigation in the Columbia Basin region of the PNW is to replenish full ET irrigation (Lang et al. 1999). This recommendation was based on the data of J. Stark (unpublished 19961 ). To date no refereed publication exists on the long-term evaluation of the effects of different irrigation regimes on any potato cultivar under highproduction growing conditions in the Northwest. The objective of this study was to examine the effects of mild deficit irrigation applied three to four weeks after seedling emergence through tuber bulking stage on tuber yield and quality of potato cultivars in high-production growing conditions under center pivot irrigation. MATERIALS AND METHODS Field experiments were conducted in 2004, 2006, and 2007 in Benton County, Washington, on a Quincy fine sand (mixed, mesic Xeric Torripsamments) under a center pivot irrigation system (Lindsay 1 Effects of irrigation and nitrogen management on potato quality. Washington Potato Information Exchange. Pasco, WA. May 29, 1997. Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 214 A. K. Alva et al. Manufacturing Co., Lindsay, NE, pivot water application efficiency = 85%). A factorial split-plot design with five replications was used. In the 2004 study, the only cultivar used was Ranger Russet, while both Ranger Russet and Umatilla Russet cultivars were used in 2006 and 2007. Planting was done in 20- to 30-cm-high raised beds spaced 86 cm apart, with 45,500 plants·ha−1 . The irrigation regimes (main treatment) used in this study were irrigation to replenish full ET on a daily basis or DI. The target DI in relation to the amount of water applied for the full ET treatment was 30% in 2004 and 20% in 2006 and 2007. The DI treatments began three to four weeks after seedling emergence (Table 1). As a result, the actual total irrigation amount over the growing season in the DI treatment represented 20%, 17%, and 14% deficit during 2004, 2007, and 2006, respectively, as compared to the total irrigation for the full ET treatments for the respective years (Table 1). The ET was calculated using the American Society of Civil Engineers’ standardized Penman-Monteith equation (Howell et al. 2005) using a weather station at the experiment site that was part of the Washington State UniversityAgriculture Weather Network. Cumulative ET and irrigation during each of the three growing years are summarized in Table 1. Sub-treatments included three pre-plant N rates of 56, 112, or 168 kg·ha−1 (zero N treatment was included only in 2004) as urea (46% N) broadcast applied to soil and incorporated during tillage operations. Within each pre-plant N treatment, three TABLE 1 Important Dates During the Potato Growing Season in the Pacific Northwest, as Well as Cumulative Evapotranspiration (ET) for the Growing Period and Cumulative Irrigation for Replenishment of Full ET and Deficit Irrigation (DI) Treatments Parameter 2004 2006 2007 Cultivars Ranger Russet Ranger Russet & Umatilla Russet Ranger Russet & Umatilla Russet March 17 April 19 March 17 April 27 March 12 April 26 June 1 May 18 August 22 September 9 1281 June 5 May 26 August 22 August 28 1270 June 8 May 17 August 31 September 10 1344 828 823 786 815 850 843 658 700 700 Planting date Emergence of seedlings Row closure Start of DI Top killa Harvest date Cumulative Degree Days (◦ C)b (mm) Cumulative ETb Cumulative irrigation to replenish full ETb Cumulative irrigation for DIb a b Plant top vegetation is removed in preparation for tuber harvest. From seedling emergence date through top kill date. Impact of Deficit Irrigation on Potato 215 in-season N rates were applied at 145, 200, and 255 kg·ha−1 N in 2006, or 112, 224, and 336 kg·ha−1 N in 2004 and 2007. In-season N was applied using urea ammonium nitrate (32% N) as five fertigations at two-week intervals starting four weeks after seedling emergence. Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Petiole Sampling and Analysis Petiole samples were taken weekly starting four weeks after emergence (11 samplings during the growing season) and analyzed for concentrations of NO3 -N, and K. The fourth fully opened leaf from the top was sampled from 15 to 20 plants per plot between 9 and 10 A.M. each sampling. The leaflets were discarded, and only petioles were stored in an ice chest, transported to the laboratory, oven dried at 72◦ C, and ground. The ground petiole tissue (0.2 g) was extracted in 50 mL 4% acetic acid. The concentrations of NO3 -N were analyzed in a rapid flow analyzer (Model 8000, Lachet Instruments, Milwaukee, WI). The concentration of K was analyzed using inductively coupled plasma argon emission spectrometer (ICP AES, Optima 3000, Perkin Elmer, Norwalk, CT). Soil Sampling and Analyses The soil was sampled in early spring with multiple core samples from the 0 to 30 cm depth. Concentrations of NH4 -N and NO3 -N were measured in 2 M potassium chloride (KCl) extraction using a rapid flow analyzer (Lachat Instruments, Model 8000, Milwaukee, WI). Concentrations of phosphorus (P) and potassium (K) were measured in ammonium bicarbonate extraction using an inductively coupled plasma argon emission spectroscope (ICPAES; Optima 3000; Perkin Elmer Analytical Services, Boston, MA). The available soil N status (pre-plant) was used to adjust pre-plant N rates. The P and K requirements, based on the P and K status in the soil, were applied to conform to cooperative extension recommendations (Lang et al. 1999). Phosphorus was applied as monoammonium phosphate (28% P), and K as muriate of potash (50% K). Pre-plant applications were broadcast prior to tillage and hill formation. Plot size was six rows, each 12.2 m long. Industry-standard pest, disease, and weed management programs were followed each year as recommended by Lang et al. (1999) and the Washington State Cooperative Extension (2003a, b, c) for the PNW production conditions to produce high yields of high-quality processing tubers. Evaluation of Tuber Yield and Size Distribution Two middle rows, each 6.1 m long, were used for tuber yield measurement. A one-row potato digger (Braco Manufacturing Co., Moses Lake, WA) was used to dig and bag tubers for fresh weight yield determination. A subsample 216 A. K. Alva et al. Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 of tubers (approximately 10 kg) per plot was used to sort the tubers into different weight classifications (i.e., >0.340, 0.227 to 0.340, 0.113 to 0.227, <0.113 kg/tuber) using electronic weighing equipment (LectroTek Services, Wenatchee, WA). The distribution of total tuber yields in each treatment into different weight classification yield·ha−1 was calculated using percentages of tubers in different weight classifications in the subsamples. A subsample of representative tubers from each plot was used to measure specific gravity by weighing the subsamples in air and water. The data were subjected to ANOVA to identify significant treatments and/or interaction effects by ‘F test’ using the SAS program (SAS Systems for Windows, release 9.2, SAS Institute, Cary, NC). Mean separation between the significant treatments was calculated by Duncan’s multiple range test. RESULTS AND DISCUSSION The cumulative degree days (daily temperatures >10◦ C) from seedling emergence through top kill period were: 1,281◦ C, 1,270◦ C, and 1,344◦ C, respectively, for 2004, 2006, and 2007 (Table 1). The corresponding ET values were 828, 786, and 850 mm. Rapid increase in degree days occurred from June through August, which coincided with a rapid increase in ET as evident from the high growth rate of plants and tuber bulking during this period. In 2004, total tuber yield was significantly influenced by irrigation regimes, pre-plant N rates, and in-season N rates (Table 2). Tuber specific gravity was significantly influenced by pre-plant and in-season N rates but not by irrigation regimes. Irrigation regimes significantly influenced the tuber yields in >0.340 and 0.227–0.340 kg size grades. Tuber yields for the full ET and DI treatments were 87.8 and 63.5 Mg·ha−1 , respectively (Table 3). The DI resulted in a 28% reduction in total tuber yield as compared to that of the full ET irrigation. This was mainly attributed to significant reduction in yield of tubers in >0.340 and 0.227–0.340 kg size grades; therefore, the net returns from DI treatment could be considerably lower than that in the full ET treatment, since large size tubers receive greater market value. The harvest index decreased only by less than 3% across all N rates in the DI treatment compared to that at full ET, i.e., from 91.2 to 88.4, 86.2 to 83.2, and 78.8 to 77.6, respectively, for the 56 + 112, 112 + 224, and 168 + 336 kg·ha−1 N (preplant + in-season) rates during the 2004 growing season. Therefore, yield reduction in the DI treatment was not at the expense of increased vegetative growth. At full ET irrigation, the harvest index decreased from 91% to 78%, with an increase in N rate (pre-plant + in-season N) of 56 + 112 to 168 + 336 kg·ha−1 . This is indicative of increased vegetative growth with increased N rate at the expense biomass allocation to tubers. During 2006 and 2007, irrigation regime affected total tuber yield and tuber specific gravity across both years and cultivars (Table 2). Tuber yield 217 Impact of Deficit Irrigation on Potato TABLE 2 Analyses of Variance Statistics for Influence of Irrigation Regimes, and Pre-Plant and In-Season N Rates on Total Tuber Yields and Tuber Yields of Weight Categories of Potato Cultivars in Two Years Tuber yields in different weight grades (kg/tuber) Source Total yield >0.340 0.227–0.340 0.113–0.227 <0.113 Specific gravity Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 P>F (Significance of F test) 2004 Ranger Russet Irrigation (I) 0.0001 Pre-plant N 0.0236 (PPN) In-season N 0.0375 (ISN) I × PPN NS I × ISN NS PPN × ISN NS 2006 Ranger Russet Irrigation (I) 0.0001 Pre-plant N NS (PPN) In-season N 0.0001 (ISN) I × PPN NS I × ISN NS PPN × ISN NS 2006 Umatilla Russet Irrigation (I) 0.0074 Pre-plant N NS (PPN) In-season N 0.0046 (ISN) I × PPN NS I × ISN NS PPN × ISN NS 2007 Ranger Russet Irrigation (I) 0.0001 Pre-plant N NS (PPN) In-season N 0.0001 (ISN) I × PPN NS I × ISN NS PPN × ISN NS 2007 Umatilla Russet Irrigation (I) 0.0001 Pre-plant N 0.0381 (PPN) In-season N 0.0001 (ISN) I × PPN NS I × ISN NS PPN × ISN NS (NS) non-significant. P > 0.05. 0.0001 NS 0.0001 0.0043 NS NS NS NS NS 0.0002 NS NS 0.03 0.0277 0.0198 NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS 0.0080 NS NS NS 0.0262 NS 0.0072 NS 0.0165 0.0175 0.0193 NS NS NS 0.0001 NS NS NS NS NS NS NS NS NS NS NS NS NS 0.0001 NS NS NS 0.0040 NS 0.0101 NS 0.0119 NS 0.0001 0.0190 NS NS 0.0383 NS 0.0001 NS NS NS NS NS NS NS NS NS NS NS NS NS 0.0003 NS 0.0027 NS NS NS NS NS NS NS 0.0048 0.0337 0.0001 NS 0.0004 NS NS NS NS NS NS NS NS NS NS 0.0327 NS NS NS NS 0.0014 NS 0.0023 NS 0.0001 NS NS NS 0.0346 NS 0.0385 NS 0.0029 0.0043 0.0003 NS 0.0001 NS NS NS NS NS 0.0008 NS NS NS NS NS 0.0418 NS 0.0183 NS 218 A. K. Alva et al. TABLE 3 Effects of Irrigation Regime and Pre-plant and In-Season N Rates on Total Tuber Yields, Yields of Weight Category Tubers, and Tuber Specific Gravity of Potato Cultivars in Two Years. Mean Separation Statistics for Treatments with Significant F-Test Tuber yields in different weight grades (kg/tuber) Total yield >0.340 0.227–0.340 0.113–0.227 <0.113 Specific Gravity Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Mg·ha−1 2004 Ranger Russet Irrigation Full ET DIb 87.8aa 63.5b 24.4a 10.1b 30.1a 20.8b Pre-plant N(kg ha−1 ) 0 56 112 168 26.7 26.2 NS 5.6 5.6 NS 1.0872 1.0878 NS 65.0b 66.4b 78.6a 82.8a 19.8b 20.4b 27.7a 29.9a 24.6 27.4 25.2 28.6 NS 4.9 5.3 6.0 6.1 NS 1.0899a 1.0896b 1.0864b 1.0844b In-season N(kg·ha−1 ) 112 224 336 14.7 12.2 19.4 16.4 NS 73.7ab 78.5a 69.2b 13.0 19.7 14.6 NS 23.7 26.6 23.4 NS 29.8a 25.5b 25.0b 6.6a 5.6ab 5.0 b 1.0888a 1.0859b 1.0879ab 2006 Ranger Russet Irrigation Full ET DI 84.5a 78.5b 33.4a 26.4b 18.2b 21.2a 2.3b 3.2a 1.0852b 1.0889a In-season N(kg·ha−1 ) 145 200 255 25.3 24.0 NS 83.8a 84.6a 76.1b 29.9ab 34.4a 25.3b 26.4 24.4 23.2 NS 20.0 18.4 20.7 NS 2.9 2.7 2.7 NS 1.0909a 1.0902a 1.0802b 2006 Umatilla Russet Irrigation Full ET DI 72.2a 66.8b 14.0a 11.0b 41.5a 36.4b 11.9 b 14.6 a 1.0769b 1.0842a In-season N(kg·ha−1 ) 145 200 255 4.0 3.2 NS 72.0a 71.8a 64.6b 3.5 4.0 3.3 NS 12.5 13.5 11.5 NS 42.1a 38.8ab 35.9b 13.3 13.4 13.1 NS 1.0816a 1.0846a 1.0755b 2007 Ranger Russet Irrigation Full ET DI 88.5a 82.0b 28.7a 21.9b 24.2 25.6 NS 4.2 4.7 NS 1.0874a 1.0845b In-season N(kg·ha−1 ) 112 224 336 29.6 27.8 NS 79.6c 86.0b 90.1a 16.9b 28.0a 30.9a 26.8 29.6 29.7 NS 29.2a 22.6b 23.0b 4.7 4.0 4.5 NS 1.0854 1.0860 1.0865 NS (Continued) 219 Impact of Deficit Irrigation on Potato TABLE 3 (Continued) Tuber yields in different weight grades (kg/tuber) Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Total yield >0.340 0.227–0.340 0.113–0.227 <0.113 Specific Gravity 2007 Umatilla Russet Irrigation Full ET DI 78.7a 70.5b 6.4a 3.6b 18.7a 12.7b 12.0b 13.9a 1.0825a 1.0808b Pre-plant N(kg·ha−1 ) 56 112 168 40.2 39.4 NS 73.2b 76.9a 73.6b In-season N(kg·ha−1 ) 112 224 336 5.2 5.6 4.2 NS 15.9 15.7 15.4 NS 38.9 41.0 39.6 NS 12.2 13.1 13.5 NS 1.0808 1.0814 1.0826 NS 68.3b 76.9a 78.6a 2.8b 6.1a 6.2a 13.3b 16.0a 17.7a 37.5b 39.1b 42.8a 13.8 12.5 12.5 NS 1.0840a 1.0817b 1.0792c a Means followed by similar letters are not significantly different at P = 0.05 by each subset treatment comparisons. (NS) non-significant; (DI) deficit irrigation. Refer to Table 1 for percent deficit of cumulative irrigation in DI as compared to that in full ET treatment for each year. in the DI, as compared to that in the full ET irrigation, decreased by 7.1% to 7.5% and 7.3% to 10.4% across two cultivars in 2006 and 2007, respectively (Table 3). In 2007, yield reduction due to DI was greater for Umatilla Russet cultivar (10.4%) compared to Ranger Russet cultivar (7.3%). Tuber specific gravity was greater with deficit irrigation compared to that for full ET irrigation across cultivars in 2006. However, the converse trend was true in 2007. Irrigation regime influenced yield of tubers >0.340 kg in both cultivars in 2007. Yield of tubers >0.340 kg in the full ET irrigation was significantly greater by 31% and 78% compared to that in the DI treatment in Ranger Russet and Umatilla Russet cultivars, respectfully. However, in 2006 this effect was evident only in Ranger Russet cultivar (27% increase). The general trend was for greater proportion of large size tubers with full ET irrigation compared to that in the DI. Pre-plant N rate did not affect total and grade classification yields in either cultivar in 2006 and only in Ranger Russet cultivar in 2007. Tuber weight distribution is an important factor in determining net return for the product depending on market destination and intended use. In general, the Ranger Russet cultivar produced more large-weight tubers compared to the Umatilla Russet cultivar (Figures 1 to 3). In the Ranger Russet cultivar, tubers >0.227 kg accounted for 55% to 75% of total tuber yield across all treatments and years. For the Umatilla Russet cultivar, the proportion was 17% to 27%; in this cultivar 50% to 60% of total tuber yield was in 0.113 to 0.227 kg Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 220 A. K. Alva et al. FIGURE 1 Distribution of tubers into weight classifications in A) Ranger Russet and B) Umatilla Russet subject to full ET (FI) and deficit irrigation (DI) regimes in 2006 and 2007. The experiment was conducted on Quincy fine sand in the Pacific Northwest. weight. Deficit irrigation on Ranger Russet cultivar decreased the numbers of tubers >0.340 kg with concurrent increase in small weight tubers, i.e., those in the 0.113 to 0.227 and <0.113 kg ranges. In Umatilla Russet cultivar, DI increased proportion of tubers <0.113 kg and decreased that of tubers >0.227 kg. In-season N rate affected total tuber yields and some tuber weight classifications across both cultivars and years (Tables 2, 3). Total tuber yield was significantly lower at 255 kg·ha−1 in-season N compared to N rates of 145 and 200 kg·ha−1 in both cultivars in 2006. In 2007, total tuber yield was greater with increasing in-season N rates. In 2006, tuber yield of Ranger Russet cultivar yields of tubers >0.340 kg was lower at 255 kg·ha−1 N compared to that at 200 kg·ha−1 . In 2006, in-season N only affected the 0.113 to 0.227 kg tubers of Umatilla Russet cultivar, i.e., those significantly Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Impact of Deficit Irrigation on Potato 221 FIGURE 2 Distribution of tubers into weight classifications in A) Ranger Russet and B) Umatilla Russet subject to different in-season N rates delivered in five applications at twoweek intervals four weeks after seedling emergence in 2006. The experiment was conducted on Quincy fine sand in the Pacific Northwest. lower at 255 kg·ha−1 N than at 145 kg·ha−1 . In 2007 in this cultivar, yield of tubers >0.227 kg was greater at either 224 or 336 kg·ha−1 in-season N rates compared to that at 112 kg·ha−1 N. Yield of tubers 0.113 to 0.227 kg was greater at 336 kg·ha−1 in-season N than that at either 112 or 224 kg·ha−1 N rates. The status of petiole NO3 -N is a good indicator of plant-available N during the growing period. The desirable ranges of petiole NO3 -N is dependent on plant growth stage. In both years, petiole NO3 -N concentrations were greater under DI compared to those for plants under full ET irrigation in both cultivars, particularly during tuber bulking and maturation stages (Figure 4). During the tuber maturation stage, petiole NO3 -N concentrations Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 222 A. K. Alva et al. FIGURE 3 Distribution of tubers into weight classifications in A) Ranger Russet and B) Umatilla Russet subject to different in-season N rates, delivered in five applications at twoweek intervals four weeks after seedling emergence in 2007. The experiment was conducted on Quincy fine sand in the Pacific Northwest. in the DI treatment were above the desirable range of concentrations. Excess availability of N during the late growing season is undesirable as it contributes to increased sugar content that adversely affects fry color and quality. However, in this experiment, reducing sugar content in the tuber was not analyzed. This could be attributed to DI and may have decreased total aboveground biomass, increasing NO3 -N concentration in petioles, or full ET irrigation may have contributed to decreased availability of N in the root zone due to increased leaching of NO3 -N compared to that in the DI treatments. This could contribute to lower petiole NO3 -N in the full ET irrigation treatment. Petiole NO3 -N concentrations increased as the in-season N rate increased in both cultivars across 2006 and 2007 (Figures 5 and 6). In 2006, Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Impact of Deficit Irrigation on Potato 223 FIGURE 4 Petiole NO3 -N concentrations during the A) 2006 and B) 2007 growing seasons in two potato cultivars subject to two irrigation regimes, i.e., replenishment of full ET (FI) or deficit irrigation (DI). The ranges of desirable concentrations are represented by shaded boxes for the following growth stages: (i) tuberization (42 to 63 DAE), 1.5% to 2.6%; (ii) tuber bulking (63 to 84 DAE), 1.2% to 2.0%; and (iii) tuber maturation (84 DAE to harvest), 0.6% to 1.0%. (DAE) days after emergence. petiole NO3 -N concentrations across both cultivars remained within desirable ranges at the low and medium in–season N rates. At the 255 kg·ha−1 in–season N rate the petiole NO3 -N concentrations were in excess range during tuber maturation stage (Fig. 5). In Umatilla Russet cultivar at 145 kg·ha−1 N, petiole NO3 -N concentrations were at the lower limit of desirable concentrations during tuberization and tuber bulking stages. In 2007 at the 112 kg·ha−1 in-season N rate, petiole NO3 -N concentration was below the desirable range of concentrations across all stages in both cultivars (Figure 6). This may explain lower tuber yield with the 112 kg·ha−1 in-season N rate than that with increased in-season N rates in both cultivars. Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 224 A. K. Alva et al. FIGURE 5 Petiole NO3 -N concentrations during the 2006 growing season in A) Ranger Russet and B) Umatilla Russet potato cultivars subject to different in-season N rates, at five applications in two-week intervals four weeks after seedling emergence. The ranges of desirable concentrations are represented by shaded boxes for the following growth stages: (i) tuberization (42 to 63 DAE), 1.5% to 2.6%; (ii) tuber bulking (63 to 84 DAE), 1.2% to 2.0%; and (iii) tuber maturation (84 DAE to harvest), 0.6% to 1.0%. (DAE) days after emergence. Petiole K concentrations were generally greater for the Ranger Russet cultivar compared to the Umatilla Russet cultivar in both years, particularly during tuber bulking and maturation (Figure 7). Irrigation regimes had negligible effects on petiole K concentrations of cultivars in years. Petiole K concentrations across both cultivars and years. In Ranger Russet cultivar, petiole K concentrations were in excess during tuber bulking stage as well, but only in 2006. This study demonstrated that a 14% to 20% reduction in water application, as compared to irrigation to replenish full ET, resulted in 7% to 28% yield reductions. Therefore, continuous DI, begun three to four weeks Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Impact of Deficit Irrigation on Potato 225 FIGURE 6 Petiole NO3 -N concentrations during the 2007 growing season in A) Ranger Russet and B) Umatilla Russet potato cultivars subject to different in-season N rates, at five applications in two-week intervals four weeks after seedling emergence. The ranges of desirable concentrations are represented by shaded boxes for the following growth stages: (i) tuberization (42 to 63 DAE). 1.5% to 2.6%; (ii) tuber bulking (63 to 84 DAE), 1.2% to 2.0%; and (iii) tuber maturation (84 DAE to harvest), 0.6% to 1.0%. (DAE) days after emergence. after seedling emergence through to tuber maturation stage, had significant effects on tuber yield, particularly on large-size tubers under high production growing conditions. However, further studies are recommended to evaluate the economic and environmental impacts of full ET versus DI. Further studies are also recommended to evaluate the impact of short-term DI only at certain growth stages to identify the least sensitive growth stages for DI. This approach has the merit of conserving water without significant negative effects on the yield and quality of tubers, as well as net returns. Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 226 A. K. Alva et al. FIGURE 7 Petiole K concentrations during the A) 2006 and B) 2007 growing season in potato cultivars subject to irrigation regimes, i.e., replenishment of full ET (FI) or deficit irrigation (DI). The ranges of desirable concentrations are represented by shaded boxes for the following growth stages: (i) tuberization (42 to 63 DAE), 8.0% to 11.0%; (ii) tuber bulking (63 to 84 DAE), 6.0% to 9.0%; and (iii) tuber maturation (84 DAE to harvest), 4.0% to 6.0%. (DAE) days after emergence. REFERENCES Alva, A. K. 2008. Water management and water uptake efficiency by potatoes: A review. Arch. Agron. Soil. Sci. 54:53–68. Eldredge, E. P., Z. A. Holmes, A. R. Mosley, C. C. Shock, and T. D. Stieber. 1996. Effects of transitory water stress on potato tuber stem-end reducing sugar and fry color. Am. Potato J . 73:517–530. Eldredge, E. P., C. C. Shock, and T. D. Stieber. 1992. Plot sprinklers for irrigation research. Agron. J . 78:436–440 Fulton, J. M. 1970. Relationship of root extension to the soil moisture level required for maximum yield of potatoes, tomatoes, and corn. Can. J. Soil Sci. 50:92–94. Downloaded by [Professor A. K. Alva] at 09:30 17 October 2012 Impact of Deficit Irrigation on Potato 227 Howell, T. A., R. L. Elliot, R. G. Allen, I. A. Walter, and D. Itenfisu (Eds.). 2005. ASCE standardized reference evapotranspiration equation. Reston, VA: Environmental and Water Resource Institute, American Society of Civil Engineers. Kleinkopf, G. E. 1979. Translucent-end of potatoes. University of Idaho Coop. Ser. Ext. Series No. 488. Moscow, Idaho: University of Idaho, College of Agriculture, Cooperative Extension Service, Agricultural Experiment Station. Lang, N. S., R. G. Stevens, R. E. Thornton, W. L. Pan, and S. Victory. 1999. Potato nutrient management for Central Washington. Ext. Bull. 1871. Pullman, WA: Washington State University. Lynch, D. R., N. Foroud, G. C. Kozub, and B. C. Farries. 1995. 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