Evaluation of alternative mulches for blueberry over five production seasons

Authors: SULLIVAN, DAN - Oregon State University; STRIK, BERNADINE - Oregon State University; Bryla, David

Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2014
Publication Date: 5/1/2015
Citation: Sullivan, D.M., Strik, B.C., Bryla, D.R. 2015. Evaluation of alternative mulches for blueberry over five production seasons. Acta Horticulture Proceedings. 1076:171-178.

Interpretive Summary: The development of organic markets for blueberry in recent years has stimulated interest in using compost to supply organic matter (OM) and nutrients and to perhaps stimulate favorable soil microbial activity. Maintaining soil OM is especially important for blueberry because it is a long-lived perennial that is best adapted to high OM soil (20+ years). This study demonstrated a large benefit to soil OM maintenance and a small increase in berry yield resulting from yard debris compost application. These benefits did not translate into economic benefit, however, due to the high cost of weed control associated with compost use. Future trials should evaluate compost use in conjunction with less expensive weed control management systems. A potential option is to cover the compost with weed mat.

Technical Abstract: Highbush blueberry (Vaccinium corymbosum L.) is a calcifuge (acid-loving) plant that responds favorably to mulching with organic matter (OM). Until recently, most blueberry plantings in our region were grown with a mulch of douglas-fir sawdust, with additional nitrogen (N) fertilizer applied to compensate for N immobilized by sawdust decomposition. A field trial was established in 2006 in Aurora, Oregon, USA to evaluate alternative mulches (as partial or full replacement for sawdust) within a certified Organic system. Mulch treatments were: sawdust alone (9-cm depth); yard debris compost (4 cm) covered with sawdust (5 cm); and geotextile weed mat installed at planting (fall 2006) and replenished in the winter of 2010-11. Mulch treatments comprised one component of a factorial trial that included two cultivars (‘Duke’ and ‘Liberty’), two bed configurations (raised and flat), two fertilizer sources (fish emulsion and feather meal) and two fertilizer rates (low and high). Cumulative berry yield (2008-12) was highest with ‘Liberty’ fertilized with either the low or high rate of feather meal. ‘Liberty’ fertilized with feather meal had cumulative relative yield of 100% with weed mat, 95% with compost + sawdust, and 85% with sawdust mulch. Soil samples (0-20 cm) had higher K (400 mg/kg) with compost than with other mulches (250 mg/kg). At Year 5-6 after planting, soil OM was 37 g/kg with compost + sawdust, 32 g/kg with sawdust, and 30 g/kg with weed mat. Soil pH remained in the optimum range for blueberry (4.5 to 5.5) across all mulch treatments. Leaf tissue nutrient concentrations were nonresponsive to mulch treatments. Overall, this study demonstrated that application of yard debris compost provides a large benefit to soil OM maintenance and produced a small increase in berry yield. Compost also increased soil test K but has not yet affected concentrations of K, Ca, or Mg in the blueberry leaf.