Root Production, Distribution, and Turnover in Conventional and Organic Blueberry Systems

Northern highbush blueberry is a shallow-rooted crop with very fine, fibrous roots. Recently, we installed minirhizotrons (root observation tubes) in a conventional and an organic blueberry planting in western Oregon. We wanted to know exactly when and where new roots were being produced and to determine whether different fertilizer and weed management practices were affecting root production and turnover. At both sites, root production peaked once in mid- to late May, about a month prior to harvest, and again in September, about a month before dormancy each year. Most roots were located < 30 cm deep and averaged only 20–75 μm in diameter. In general, plants produced more roots in raised beds than in flat ground, with sawdust mulch than with weed mat, with granular fertilizer than with fertigation, and with no or lower rates than with higher rates of fertilizer. Plants on raised beds and grown with no or low rates of fertilizer also produced deeper roots. The average median lifespan of the fine roots was 115–135 d, but roots survived an average of 60 d longer with fertigation than with granular fertilizer. Overall, timing of root production in blueberry appears to be highly dependent on temperature, shoot growth, and fruit development, while total root production and lifespan are mostly affected by the availability of soil water and nutrients. Practices such as raised beds, sawdust mulch, and reduced fertilizer rates can be used to increase root production, while fertigation may reduce plant carbon costs associated with root turnover.