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Northern highbush blueberry (Vaccinium corymbosum L.) cultivars were evaluated from planting (Oct. 2006) through 2014 in a certified organic research site in Aurora, OR. The treatments included cultivar (Duke, Bluecrop, Reka, Bluejay, Bluegold, Draper, Legacy, Liberty,Ozarkblue, andAurora), amendment-mulch [‘‘compost+ sawdust’’ (includedpreplant amendment and a surfacemulch of either an agricultural on-farm cropwaste compost or yarddebris compost and sawdust), and ‘‘weed mat’’ (no preplant amendments but with a sawdust mulch toppedwith weedmat)]. Adding on-farm compost as a preplant amendment and as part of the mulching program increased soil pH from 4.9 to 6.9, organic matter content (OM), and calcium (Ca), magnesium (Mg), and potassium (K) levels compared with the weed mat treatment. The reduced plant growth and yield in some cultivars grown in the compost + sawdust treatmentwas likely due to the higher soil pH. ‘Bluegold’ and ‘Draper’were among the cultivars with consistently high flower bud set (40% to 57%), whereas others had consistently lowvalues (e.g., 22%to45%in ‘Bluecrop’). Thenumber of flowersperbudwas affectedonly by cultivar. There was no effect of year or amendment-mulch treatment on percent fruit set which averaged 93%during the study; however, ‘Ozarkblue’ had a significantly lower fruit set (88%) than only ‘Aurora’ (96%). Berry weight was affected by year (plant age), cultivar, and amendment-mulch treatment. ‘Ozarkblue’ produced the largest berries. Type of amendmentmulch had little effect on berry weight, except in ‘Ozarkblue’, ‘Aurora’, and ‘Reka’ where plants grown with weed mat produced larger fruit than those grown with compost + sawdust. On average, ‘Bluejay’, ‘Draper’, and ‘Liberty’ fruit had the highest percent soluble solids (TSS) and ‘Ozarkblue’ the lowest. Fruit harvested fromplants grownwithweedmatwere firmer than when compost + sawdust was used. ‘Draper’ fruit were much firmer than those of the other cultivars in all years of the study.Thenumberof flowerbudsperplantmultipliedby thenumber of flowers/bud and berry weight (cultivar specific) and average fruit set was a good predictor of yield in young plants. Yield per plant increased from the second through seventh growing seasons as plantsmatured in all cultivars except for ‘Duke’ which had the greatest yield in 2014. Cumulative yield was highest in ‘Legacy’ and lowest in ‘Bluejay’ and in ‘Draper’, which had relatively low yield when plants were young.Most cultivars had greater yield when grownwith weed mat, whereas ‘Bluegold’ and ‘Liberty’ were unaffected by amendment-mulch treatment. Because weeds weremanaged in all plots, the cultivar response to amendment-mulchwas likely a reflection of sensitivity to preplant amendmentwith on-farmcompost and the resulting higher soil pH. It is possible that the cultivars differed in their adaptability to the various fertility regimes caused by the amendment-mulch treatments and fertilizers used in our study. The Pacific northwestern United States is an important region for production of cultivated blueberry (Vaccinium spp.) (U.S. Department of Agriculture, 2014). The proportion of total U.S. blueberry production grown on certified organic and exempt organic (less than $5000/year gross income and not requiring certification) farms was relatively small (3%) in 2008 (U.S. Department of Agriculture, 2010). However, the Pacific northwestern region accounted for 49% of the total blueberry organic area planted in the United States in 2008, when the last survey was conducted. The certified organic area has grown considerably since the last survey, increasing to an estimated 915 ha in Oregon and Washington in 2011, 55% of total U.S. organic blueberry area (Strik, 2014). By 2014, the organic blueberry area in Oregon and Washington accounted for about 20% of total blueberry area planted. Growth in organic production continues as consumer demand for organic products remains strong, and this region offers substantial advantages for organic production (DeVetter et al., 2015; Strik, 2016; Strik et al., 2016; Strik and Yarborough, 2005). Awide range of cultivars are grown in this region for the fresh and processed markets, offering a range in fruiting seasons from the earliest (‘Duke’) to the latest (‘Aurora’) (Strik et al., 2014). The development of yield and fruit quality of the range of cultivars grown has not been compared in research studies, likely because of the relatively long time from planting to maturity (about 8 years). Differences in the performance of cultivars have been found in organic production of ‘Duke’ and ‘Liberty’ blueberry (Larco et al., 2013a, 2013b; Strik, 2016; Strik et al., 2016) and various blackberry cultivars (Fernandez-Salvador et al., 2015). Blueberry plants are adapted to soils with low pH (4.5–5.5) and high OM (>4%) (Hart et al., 2006). Organic and conventional growers are interested in using composts because of hypothesized OM, nutrient, and microbiological benefits (e.g., Forge et al., 2003) on soil properties and nutrients. Because organic sources of nitrogen (N) are expensive and often laborious to apply, the potential benefit from a slow-release N from compost is also of great interest to growers. However, use of plantand animal-based composts as a preplant amendment may be problematic in this crop as these materials have a high pH and often a high salt content (animal-based) (Sullivan et al., 2014). Our objective was to characterize yield and associated plant and fruit quality traits of important highbush blueberry cultivars in the region from planting to maturity and evaluate their adaptation to common organic amendments and mulches used in certified organic production. Materials and Methods Study site. The study was established in Oct. 2006 at Oregon State University’s North Willamette Research and Extension Center, Aurora, OR (NWREC; lat. 45 28# N, long. 122 76# W). Weather data for this site are available from an AgriMet weather station (U.S. Deptartment Interior, 2014). The planting was certified as meeting the USDA organic criteria before the first fruit harvest year (2008) by a USDA-accredited agency (Oregon Tilth, Corvallis, OR). The soil at the site is aWillamette silt loam (fine-silty mixed superactive mesic Pachic Ultic Argixeroll) and had a pH of 4.9 and 3.7% OM. Details on Received for publication 27 Mar. 2017. Accepted for publication 28 Apr. 2017. The authors appreciate the valuable assistance of Gil Buller, former Senior Faculty Research Assistant and Emily Vollmer, former Faculty Research Assistant at the North Willamette Research and Extension Center, OSU. We appreciate the funding support provided by the Oregon Blueberry Commission. Professor. Faculty Research Assistant. Research Geneticist. Corresponding author. E-mail: bernadine.strik@ oregonstate.edu. 844 HORTSCIENCE VOL. 52(6) JUNE 2017 preplant site preparation can be found in Larco et al. (2013a). After adding any preplant amendments, if used (see below), raised beds were constructed using a bed shaper; beds were 0.3-m high and 0.4-m wide at the top and 1.5-m wide at the base when established, but settled to a height of 0.25 m by Autumn 2007. Plants were irrigated using a single line of polyethylene drip tubing (Netafim, Fresno, CA) with 2 L·h pressure-compensating, inline emitters spaced every 0.3 m. The line was located along the row near the base of plants, under the mulch. Irrigation was controlled by electric solenoid valves and an automatic timer set weekly and scheduled to maintain a soil water content suitable for highbush blueberry production [25% to 30% soil water content from the soil surface to 0.3 m, based on time domain reflectometry measurements (SoilMoisture Equip. Corp., Santa Barbara, CA)] (L. Valenzuela-Estrada, unpublished data). Amendment and mulch. Two preplant amendment-mulch treatments were evaluated. The ‘‘compost + sawdust’’ treatment included a preplant amendment and a mulch of compost and sawdust. Commercially available agricultural crop waste compost (Wilt Farms, Corvallis, OR) made on farm ( 2-cm deep centered on the row; 76 m·ha) and fresh douglas fir sawdust (Pseudotsuga menziesiiM.; 5-cm deep; 200m·ha) were incorporated before forming the raised beds in Sept.–Oct. 2006. The on-farm compost consisted of well-composted rye grass clippings and other agricultural crop waste products and had lime (107 kg·t dry weight) added during the composting process based on the carbonate content of the raw material (note Ca content in Table 1). Immediately after planting, the beds were mulched with additional on-farm compost ( 2-cm deep; 76m·ha), and then, the compost was topped with sawdust ( 7.5-cm deep; 300 m·ha) with a goal of creating a barrier to weed establishment. The mulches were spread mechanically in 0.75 m wide strips under and on each side of the plant rows. Onfarm compost was used when the mulch needed replenishing in Autumn 2007, but in Jan.–Feb. 2011 and 2013, compost made with municipal yard waste clippings was used (Rexius, Eugene, OR). The composts and sawdust were analyzed by Soil Control Laboratory (Watsonville, CA) and total nutrient application was calculated (Table 1). The second amendment-mulch treatment, ‘‘weed mat,’’ involved no preplant amendments, but included a mulch of fresh douglas fir sawdust ( 7.5-cm deep; 300 m·ha) topped with black, woven polyethylene groundcover (water flow rate of 6.8 L·h·m and a density of 0.11 kg·m as measured by the manufacturer; TenCate Protective Fabrics, OBCNorthwest, Canby, OR).Weed mat was placed over a sawdust mulch layer, not currently a commercial practice, with a goal of offsetting the reduction in soil OM observed under weed mat mulch in long-lived perennial crops such as apple (Malus ·domestica Borkh.) (Choi et al., 2011). The weed mat was 1.5-m wide and was centered over the planting beds before securing it in place with landscape staples. A 20-cm diameter hole was cut in the weed mat for each plant and the are

Northern Highbush Blueberry Cultivars Differed in Yield and Fruit Quality in Two Organic Production Systems from Planting to Maturity