ORGANIC HIGHBUSH BLUEBERRY PRODUCTION SYSTEMS RESEARCH - MANAGEMENT OF PLANT NUTRITION, IRRIGATION REQUIREMENTS, WEEDS AND ECONOMIC SUSTAINABILITY

A 0.4 ha planting was established in October 2006 to evaluate the effects of cultivar (‘Duke’ and ‘Liberty’), bed type (“flat ground” and raised beds), weed management (sawdust mulch and hand weed control; compost plus sawdust mulch with acetic acid, flaming, and hand control used as needed; and landscape fabric (weed mat)) and type and rate of fertilizer (feather meal and liquid fish emulsion at 29 and 57 kg•ha^-1 N) on plant growth, yield, fruit quality, and establishment and main¬tenance costs in highbush blueberry. The site was certified organic in 2008. Before planting, soil was a clay loam with 3.7% organic matter content and pH 4.9. Plants grown on raised beds were larger and produced greater yield than those on flat ground. However, raised beds, particularly with weed mat (which increased soil temperature by 5°C), required up to 269 L/plant/season more irrigation than flat ground plantings to maintain similar levels of soil moisture. Weeds never exceeded 20-25% coverage in any treatment in 2007-2009, although weed mat resulted in the fewest weeds while compost plus sawdust resulted in the most. Although flaming was used in the spring along with acetic acid applied every 3 weeks during the summer in plots mulched with sawdust and compost, hand-weeding was still required in all treatments including those with weed mat. In 2009, the third growing season, yield averaged 1.7 kg/plant and was highest with 29 kg•ha^-1 N of fish emulsion or 57 kg•ha^-1 N of feather meal and lowest with 57 kg•ha^-1 N of fish emulsion. Yield was also higher with weed mat or sawdust plus compost than with only sawdust. Fruit firmness was likewise affected by fertilizer and mulch as fruits were firmer with fish and softer with weed mat. Cumulative net production costs (years 0-3) varied as much as 60% among treatments, ranging from -$ 32,690/ha to -$ 51,990/ha (net loss).