Evaluation of Conventional and Alternative Nitrogen Fertigation Methods in Highbush Blueberry

A 0.3-ha study was planted in Oct. 2008 to determine the effects of nitrogen (N) fertigation using conventional and alternative drip irrigation systems on shoot growth and early fruit production in six cultivars of northern highbush blueberry (Vaccinium corymbosum L.).  The cultivars included ‘Earliblue’, ‘Duke’, ‘Draper’, ‘Bluecrop’, ‘Elliott’, and ‘Aurora’.  The conventional drip system consisted of two laterals of drip tubing, with 2 L·h^-1 in-line emitters spaced every 0.45 m, placed on each side of the row, at a distance of 0.2 m from the base of the plants. The alternative system was called KISSS (kapillary irrigation sub surface system) and consisted of a single lateral of drip tape covered with geo-textile fabric that dispersed water and nutrients along the entire length.  A single KISSS lateral was placed along the row near the base of plants.  Liquid urea was applied at rates of 100 and 200 kg·ha^-1 N with conventional drip and 200 kg·ha^-1 N with KISSS.  Fertigation was done weekly from early May to mid August during the first year after planting in 2009 and from mid April to mid August the following 2 years. Irrigation was scheduled every 1–3 days to replace 100% crop evapotranspiration.  Plants were cropped beginning the third year after planting.  Shoot growth differed among cultivars each year and between irrigation systems the first 2 years but was not affected by irrigation system the third year or by N rate and treatment interactions in any year.  In the first year after planting, fertigation with KISSS produced an average of 1.8–2.0 cm/shoot more growth than conventional drip fertigation.  The following year, the opposite occurred and fertigation with conventional drip produced 3.2 cm/shoot more growth than KISSS.  By the third year, shoot growth and plant size were similar between irrigation systems.  Fruit yield also differed among cultivars the third year and averaged 3.4–9.7 t·ha^-1; however, like shoot growth in year 3, yield was unaffected by irrigation system, N rate, or any interactions.  Plant growth and yield were not a function of leaf N concentration, as leaf N was consistently lower each year with 100 kg·ha^-1 N than with 200 kg·ha^-1 N and similar between drip and KISSS fertigation with 200 kg·ha^-1 N.  Overall, plant establishment differed little between the two fertigation methods, and 100 kg·ha^-1 N or less was sufficient to maximize early fruit production in each cultivar.