Root production, distribution, and turnover in conventional and organic northern highbush blueberry systems

Authors: Bryla, David; VALENZUELA-ESTRADA, LUIS - Oregon State University; VARGAS, OSCAR - Dole Fresh Vegetables

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 1/4/2017
Publication Date: 11/1/2017
Citation: Bryla, D.R., Valenzuela-Estrada, L.R., Vargas, O.L. 2017. Root production, distribution, and turnover in conventional and organic northern highbush blueberry systems. Acta Horticulturae. 1180:169-176.

Interpretive Summary: Northern highbush blueberry (Vaccinium corymbosum L.) 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 micrometers in diameter. In general, plants produced more roots in raised beds than in flat ground, with sawdust mulch than with geotextile landscape fabric, 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 median lifespan of the fine roots ranged from 84–184 days in the conventional planting and 194–393 days in the organic planting. Roots in the conventional planting survived an average of 58 days longer with fertigation than with granular fertilizer, and roots in the organic planting survived an average of 100 days longer with low rate of fish emulsion than with a higher rate when the plants mulched with the geotextile fabric. 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 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.

Technical Abstract: Northern highbush blueberry (Vaccinium corymbosum L.) 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 micrometers in diameter. In general, plants produced more roots in raised beds than in flat ground, with sawdust mulch than with geotextile landscape fabric, 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 median lifespan of the fine roots ranged from 84–184 days in the conventional planting and 194–393 days in the organic planting. Roots in the conventional planting survived an average of 58 days longer with fertigation than with granular fertilizer, and roots in the organic planting survived an average of 100 days longer with low rate of fish emulsion than with a higher rate when the plants mulched with the geotextile fabric. 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 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.