Effects of nitrogen rate and application method on early production and fruit quality in highbush blueberry

Authors: EHRET, D - Agriculture And Agri-Food Canada; FREY, B - Agriculture And Agri-Food Canada; FORGE, T - Agriculture And Agri-Food Canada; HELMER, T - Agriculture And Agri-Food Canada; Bryla, David; ZEBARTH, B - Agriculture And Agri-Food Canada

Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2014
Publication Date: 9/1/2014
Citation: Ehret, D.L., Frey, B., Forge, T., Helmer, T., Bryla, D.R., Zebarth, B.J. 2014. Effects of nitrogen rate and application method on early production and fruit quality in highbush blueberry. Canadian Journal of Plant Science. 94(7):1165-1179.

Interpretive Summary: Many blueberry fields in North America are irrigated by drip. In addition to efficient water use, drip irrigation also offers the opportunity to inject fertilizers through the irrigation system, often referred to as fertigation. The purpose of this study was to compare the effects of fertigation with liquid nitrogen (N) fertilizer to standard surface applications of granular N fertilizer on fruit production in highbush blueberry and to identify the optimum amount of N needed with each method. We hypothesized that N fertigation would be more efficient than granular N application and would result in not only higher yields with less fertilizer but also in better fruit quality. Indeed, over a four-year period, fertigation produced higher yields, more flowers, larger plants, and higher anthocyanin concentrations in the fruit with equal or less amounts of N than split applications of granular fertilizer. Fertigation is therefore recommended in drip-irrigated blueberry fields.

Technical Abstract: A field study was conducted to examine the effects of nitrogen (N) rate and method of N fertilizer application on growth, yield, and fruit quality in highbush blueberry (Vaccinium corymbosum L.) during the first 4 years after planting in south-coastal BC. Nitrogen was applied at 0-150% of current production guide rates either with three equal applications of broadcast granular ammonium sulphate each spring or by fertigation through the drip irrigation system with 10 equal applications of liquid ammonium sulphate injected bi-weekly from early spring to late summer each year. Yield increased with increasing N rate during the second and third years of fruit production, and the response, not only in terms of yield but also in terms of flower number and plant size, was greater with fertigation than with broadcast fertilizers. Fruit firmness also increased consistently with higher N rates, while fruit size either increased or decreased, depending on year. There were no effects of N on fruit oxygen radical absorbance capacity (ORAC), titratable acidity, or soluble solids. However, the composition of fruit anthocyanins changed, with seven anthocyanins decreasing and three others increasing with N rate. In two out of the three years, total anthocyanin concentration was higher in fertigated than in broadcast treatments. Soil ammonium and nitrate concentrations increased with N rate, but only soil nitrate differed between the two application methods. Soil nitrate was higher with fertigation than with granular fertilizers, particularly at the end of the season and when higher rates of N were applied. In summary, fertigation produced more shoot growth and higher yields with less N than broadcast applications of fertilizer and is therefore recommended in drip-irrigated blueberry fields.