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Using compost as mulch for highbush blueberry.

Forge, T.A., Temple, W., and Bomke, A.A. (2013). "Using compost as mulch for highbush blueberry.", Acta Horticulturae (ISHS), 1001, pp. 369-376.


In coastal British Columbia and adjacent areas of the Pacific Northwest, beds of blueberry are usually mulched with conifer sawdust (SD), which is very effective at deterring weed growth, moderating soil temperature and moisture, and maintaining pH in the range optimal for blueberry. However, the high C/N ratio of SD mulch can stimulate microbial immobilization of nitrogen (N), necessitating the application of fertilizers in excess of actual crop requirements in order to avoid crop N deficiency. Mulches of compost may not require supplemental N, but the compatibility of compost mulch with blueberry production is not well known. We compared SD to yard waste compost (YWC) mulch and bare soil with respect to effects on soil chemical properties, macronutrient dynamics, mycorrhizal colonization of roots, and crop response; all three treatments were covered with woven polyethylene weed mat for supplemental weed suppression. Yard waste compost reduced berry size and indicators of blueberry vegetative growth relative to SD. It also increased leaf N and K, but reduced leaf Mg to deficiency levels. Soil electrical conductivity (EC) increased after YWC application to levels considered detrimental to blueberry root growth. Likewise, soil pH increased under YWC relative to SD. Yard waste compost also suppressed mycorrhizal colonization and diversity relative to SD. We conclude that yard waste compost should not be applied alone as mulch to blueberry, but it can be used effectively along with SD to mitigate the N-immobilizing tendency of SD mulch.

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