|Authors: ||D.M. Sullivan, B.C. Strik, D.R. Bryla|
|Keywords: ||Vaccinium corymbosum, compost, sawdust, weed mat, landscape fabric, raised beds, nutrient, nitrogen|
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 northwestern United States 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 Oct. 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.
The treatments were applied at planting and 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). The organic mulches were reapplied, and the weed mat was replaced, after four growing seasons.
Average cumulative yields over the first 5 years of fruit production (2008-12) were 9.0 kg/plant with sawdust, 9.3 kg/plant with ‘compost + sawdust’, and 9.6 kg/plant with weed mat; and the treatment with the highest cumulative yield, regardless of mulch, was ‘Liberty’ fertilized with either a low or high rate of feather meal.
By 5-6 years after planting, soil OM was 37 g∙kg-1 with ‘compost + sawdust’, 32 g∙kg-1 with sawdust, and 30 g∙kg-1 with weed mat.
Soil pH remained in the optimum range for blueberry in each treatment (pH 4.5-5.5), but soil K at a depth of 0-20 cm was higher with ‘compost + sawdust’ (400 mg∙kg-1) than with sawdust or weed mat (250 mg∙kg-1 each). Leaf nutrient concentrations, including K, Ca, and Mg, were nonresponsive to the mulch treatments.
Overall, this study demonstrated that application of yard debris compost provided a large benefit to soil OM maintenance and increased soil test K, but had no effect in 6 years on tissue nutrient concentrations in the blueberry leaves.
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