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J. R. Davenport

Foliar feeding of crop plants is an increasingly popular practice. The use of foliar nutrients relies on the ability of the plant to sorb nutrients through the leaves. Cranberries (Vaccinium macrocarpon Ait.) are known to have a waxy cuticle on the leaf surface which may impede nutrient uptake, leaving only the lower leaf surface for effective uptake. This study was undertaken to determine the extent of foliar nutrient uptake by cranberries using rubidium as a tracer. Rubidium was chosen for its similarity to potassium in plant uptake. In replicated plots, cranberries were sprayed with rubidium at the rate recommended for foliar potassium at three different growth stages and three different times of day. Washed and unwashed leaves were analyzed one day, one week, and one month after rubidium applications. Stem, soil, and root material was analyzed for rubidium at the one week and one month sample times. Results will be discussed with reference to uptake and movement of foliar applied nutrients in cranberries.

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J. R. Davenport and C. J. DeMoranville

Like many fruit crops, the difference between vegetative and reproductive production in cranberry is strongly influenced by nitrogen supply, as is fruit quality. However, the optimal supply for this crop has not been established. Further, there have been mixed results on whether or not cranberry can metabolize nitrate nitrogen. Within the past 6 years there has been an upsurgence in research on cranberry nitrogen nutrition and it has started to provide answers to some of these unknowns. Results from the lab of L. Peterson (U Wi - Madison) have shown that cranberry will take up nitrate nitrogen, however the uptake is minimal unless ammonium nitrogen is present. The work from Peterson's lab has also shown that there is some nitrate reductase activity in cranberry leaves, albeit at very low levels. Work that we have conducted and work by J. Hart's group (OSU) have been the basis for establishing optimal nitrogen rates and timings for cranberry in the different growing areas in North America. Overall, the work from these different groups has shown that except in extreme situations, 22 - 33 kg N/ha is optimal for cranberry production. However, timing of application varies widely due to weather conditions in the different growing areas.

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M.J. Hattendorf and J.R. Davenport

Cranberry (Vaccinium macrocarpon Ait.) evapotranspiration (ET) has not been documented. Micrometeorological techniques based on canopy temperature minus air temperature were used to estimate ET on `Stevens' and `Crowley' cranberry at Long Beach (lat. ≈46°20′N, long. 124°W) and Grayland (lat. ≈46°47′N, long. 124°W), Wash., in 1991 and 1992, respectively. Cranberry ET was 55% of Priestley–Taylor reference ET and ranged from <0.5 to >4 mm·d–1. The Priestley–Taylor reference ET was a very good predictor of cranberry ET (r 2 = 0.795). Running 7-day cumulative ET ranged from 7 to 17 mm·week–1.

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Joan R. Davenport and Mary J. Hattendorf

Potatoes (Solanum tuberosum L.) are grown extensively throughout the Pacific northwestern United States as a high value crop in irrigated rotations with other row crops such as wheat (Triticum aestivum L.) and both field and sweet corn (Zea mays L.). Center pivots are the predominant irrigation systems. Soil texture ranges from coarse sands to finer textured silt loams and silts and can vary within one field, particularly in fields with hilly topography. Site specific management is being evaluated as an approach to help to optimize inputs (water, seed, agricultural chemicals) to maintain or enhance yield and reduce potential negative environmental impacts from these farming systems. Currently, variable rate fertilizer application technology and harvest yield monitoring equipment are commercially available for potato. Variable rate seeding and variable rate irrigation water application technologies are developed but not fully commercialized and variable rate pesticide application equipment is in development. At the Irrigated Agricultural Research and Extension Center in Prosser, Wash., we have a team of research scientists, interested individuals from local industry, and other key organizations (e.g. local conservation districts) who are working together to evaluate different site specific technologies, improve the ability to use available tools, and to improve decision-making ability by conducting research both on farm and in research plots.

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K.M Whitley and J.R Davenport

Potato (Solanum tuberosum) production in Washington State's Central Columbia Plateau faces nitrogen (N) management challenges due to the combination of coarse textured soils (sandy loam to loam) and hilly topography in this region as well as the high N requirement of potato. Potato growth and development can vary with the N availability across the field. In this 2-year study, two adjacent potato fields were selected each year (1999 and 2000). Each field was soil sampled on a 200 × 200 ft (61.0 m) grid to establish existing soil N content. One field was preplant fertilized with variable N rate while the other was conventionally preplant fertilized, applying a uniform rate across the field based on the field average. During the growing season, each field was monitored for nitrate leaching potential using ion exchange membrane technology. Soil and plant nutrient status were also monitored by collecting in-season petiole and soil samples at two key phenological stages, tuber initiation and tuber bulking. Overall this research showed that variable rate preplant N fertilizer management reduced N leaching potential during the early part of the growing season, but did not persist the entire season. Since preplant N accounted for only 40% of the total seasonal N applied, it is possible that further gains could be made with variable rate in-season N application or with variable rate water application.

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Carolyn J. DeMoranville and Joan R. Davenport

It has been speculated that cranberries are susceptible to chloride injury. If this is the case, it is possible that applications of high rates of 0-0-60 (KCl) fertilizer as a K source could be detrimental to cranberry productivity. Grower anecdotes of using 0-0-60 to “shut down the plants” persist. Supposedly, using 225+ kg·ha-1 of this material slows or arrests vegetative growth. In fact, growers have claimed it can overcome the production of rank vegetation that results when too much N fertilizer has been applied. Field plots were initiated to determine the suitability of KCl and to determine if high K rates could overcome the deleterious effects of excess applied N. Plots were set up in a split-block plot design with N doses [three each “normal” (28-34 kg·ha-1 N) vs. “high” (56-67 lb N/A)] in one direction and potassium/chloride treatments in the other direction (KCl or K2SO4 at 115 or 225 kg K2O; CaCl2 to give the equivalent Cl as in the high-rate KCl treatment, and a nontreated control) for a total of 36 2 × 2-m plots per each of three cultivar locations. Plots were treated and evaluated for three consecutive years. There were no significant differences in yield among the K2SO4 and KCl treatments, indicating that at rates as high as 225 kg·ha-1 K2O, 0-0-60 and 0-0-50 perform similarly. Further, treatment with CaCl2 had no significant effect on yield. In the third year, plots receiving no K treatment had significantly lower yield than those receiving either rate or form of K (single degree of freedom comparison, significant at 0.03). These results indicate that at the rates used in this study, KCl is an adequate K source. The effect of N rate was more pronounced than that of the K treatments. In years two and three, the low N rate strips had significantly greater yield compared to that in the high N rate strips. By year two, the high N strips were visually different, with rank overgrowth. There was no significant interaction of N rate and the K treatments. While there was a trend for greater difference between the 0 K and 115 kg K rates in the high N plots compared to the moderate N plots, the addition of K never entirely overcame the negative yield effects of high N rate.

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Joan R. Davenport, Markus Keller, and Lynn J. Mills

Although the inland Pacific Northwest has a warm climate during the growing season, grapes grown in this region may be exposed to colder than optimal temperatures at several times during the year. In addition to damage from spring and fall frosts, intermittent winters with little to no snow cover and subzero temperatures can cause vine dieback and death. Temperature patterns in the recent past indicate that both fall and midwinter are times when risk of bud damage from cold events is probable, making proper site selection and cultivar choice critical. Water is not used for frost protection in this climate, but wind machines have proven to be useful. In frost-prone sites, annual sucker growth with cane burying is practiced as an insurance strategy. Modifying pruning strategies has not been shown to be advantageous after fall cold events. If rootstocks are used, research has shown greater scion survival with higher graft positions.

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J.R. Davenport, C.A. Redulla, M.J. Hattendorf, R.G. Evans, and R.A. Boydston

An accurate yield map is imperative for successful precision farming. For 3 years (1998 to 2000) two to four potato (Solanum tuberosum) fields on a commercial farm in southeastern Washington were yield-monitored using commercial yield monitoring equipment without operator interaction. Multiple potato diggers were used to harvest the fields and diggers used were not necessarily the same at each harvest. In all years, yield monitoring data were missing due to equipment failure or lack of yield monitoring equipment on all diggers. Banding, due to dissimilar calibrations, different equipment used, or differential digger performance was observed in 1998 and 2000. Based on experience described here, some yield monitor data need minimal postprocessing or correction, other data need substantial postprocessing to make them usable, and other data may not be reliable due to equipment failure, improper calibration, or other causes. Even with preharvest calibration, it is still likely that the potato yield monitor data will need differential postprocessing, indicating that yield maps lack accuracy. In addition, comparison to yield data collected at multiple points within the field, this study found that the yield monitor over estimated potato yield. Thus, with some postprocessing, a useful yield map showing within field differences is possible. However, without significant postprocessing, the practice of using multiple diggers and yield monitors for potato harvest, both within and between fields, severely limits the ability to make consistent yield maps in commercial potato operations.

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B.C. Strik, T.R. Roper, C.J. DeMoranville, J.R. Davenport, and A.P. Poole

Biennial bearing has long been thought to occur in cranberry (Vaccinium macrocarpon Ait). Researchers have shown that percent return bloom on fruiting uprights can range from 12% to 65% depending on year, bed vigor and cultivar. Resource limitation and/or hormonal factors in a fruiting upright may be related to flower bud initiation and, thus, percent return bloom the following year. This research was undertaken to determine the extent of biennial bearing by cranberry cultivar and growing region. Seven cultivars were studied; three found in all states (MA, NJ, WI, OR), two common to MA and NJ, and two different cultivars in WI and OR representing cultivars commercially grown in these areas. In the fall or winter of 1989/1990 six 2-m transects were randomly selected within a cranberry bed for each cultivar. Along the transect, 60 uprights that fruited in 1989 were tagged. In the summer of 1990, fifty of the uprights will be sampled to determine percent return bloom and percent set.

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B.C. Strik, T.R. Roper, C.J. DeMoranville, J.R. Davenport, and A.P. Poole

Biennial bearing has long been thought to occur in cranberry (Vaccinium macrocarpon Ait). Researchers have shown that percent return bloom on fruiting uprights can range from 12% to 65% depending on year, bed vigor and cultivar. Resource limitation and/or hormonal factors in a fruiting upright may be related to flower bud initiation and, thus, percent return bloom the following year. This research was undertaken to determine the extent of biennial bearing by cranberry cultivar and growing region. Seven cultivars were studied; three found in all states (MA, NJ, WI, OR), two common to MA and NJ, and two different cultivars in WI and OR representing cultivars commercially grown in these areas. In the fall or winter of 1989/1990 six 2-m transects were randomly selected within a cranberry bed for each cultivar. Along the transect, 60 uprights that fruited in 1989 were tagged. In the summer of 1990, fifty of the uprights will be sampled to determine percent return bloom and percent set.