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

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'' (included preplant amendment and a surface mulch of either an agricultural on-farm crop waste compost or yarddebris compost and sawdust), and "weed mat'' (no preplant amendments but with a sawdust mulch topped with weed mat)]. 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 treatment was 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 low values (e. g., 22% to 45% in 'Bluecrop'). The number of flowers per bud was affected only 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 from plants grown with weed mat were firmer than when compost + sawdust was used. 'Draper' fruit were much firmer than those of the other cultivars in all years of the study. The number of flower buds per plant multiplied by the number 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 grown with weed mat, whereas 'Bluegold' and 'Liberty' were unaffected by amendment-mulch treatment. Because weeds were managed in all plots, the cultivar response to amendment-mulch was likely a reflection of sensitivity to preplant amendment with on-farm compost 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.