Irrigation and Fertigation with Drip and Alternative Micro Irrigation Systems in Northern Highbush Blueberry

The use of conventional drip and alternative micro irrigation systems were evaluated for 3 years in six newly planted cultivars (Earliblue, Duke, Draper, Bluecrop, Elliott, and Aurora) of northern highbush blueberry (Vaccinium corymbosum L.). The drip system included two lines of tubing on each side of the row with in-line drip emitters at every 0.45 m. The alternative systems included geotextile tape and microsprinklers. The geotextile tape was placed alongside the plants and dispersed water and nutrients over the entire length. Microsprinklers were installed between every other plant at a height of 1.2 m. Nitrogen was applied by fertigation at annual rates of 100 and 200 kg·ha N by drip, 200 kg·ha N by geotextile tape, and 280 kg·ha N by microsprinklers. By the end of the first season, plant size, in terms of canopy cover, was greatest with geotextile tape, on average, and lowest with microsprinklers or drip at the lower N rate. The following year, canopy cover was similar with geotextile tape and drip at the higher N rate in each cultivar, andwas lowest withmicrosprinklers in all but ‘Draper’. In most of the cultivars, geotextile tape and drip at the higher N rate resulted in greater leaf N concentrations than microsprinklers or drip at the lower N rate, particularly during the first year after planting. By the third year, yield averaged 3.1–9.1 t·ha among the cultivars, but was similar with geotextile tape and drip at either N rate, and was only lower with microsprinklers. Overall, drip was more cost effective than geotextile tape, and fertigation with 100 kg·ha N by drip was sufficient to maximize early fruit production in each cultivar. Microsprinklers were less effective by comparison and resulted in white salt deposits on the fruit. Until recently, most blueberry fields in the United States were irrigated with sprinklers. However, many new plantings are irrigated by drip, particularly in newer growing regions such as California and eastern Oregon and Washington (Strik and Yarborough, 2005). Microsprinklers are also used occasionally for irrigation of blueberry (Haman et al., 1997). Blueberry plants irrigated by drip require about half as much water as those irrigated by sprinklers or microsprinklers (Bryla et al., 2011), but drip occasionally produces inferior fruit quality (softer fruit with lower soluble solids concentrations) (Bryla et al., 2009) and may result in root rot (Bryla and Linderman, 2007). Drip resulted in a lower cumulative yield than microsprinklers in a 7-year study on blueberry in Chile (Holzapfel et al., 2004). Soluble N fertilizers such as ammonium sulfate, urea ammonium nitrate, and liquid urea are easily injected and applied through drip and microsprinkler systems and are commonly used for fertigation in vine and tree fruit crops (Bar-Yosef, 1999; Kafkafi and Tarchitsky, 2011; Schwankl et al., 1998). The practice often results in more growth and yield than equivalent rates of granular fertilizer, including in highbush blueberry (Bryla andMachado, 2011; Ehret et al., 2014; Vargas and Bryla, 2015). Some advantages of fertigation may include greater fertilizer use efficiency, a lower risk of ‘‘salt burn,’’ and reduced energy and labor costs (Burt et al., 1998). However, disadvantages of fertigation may include higher fertilizer and equipment costs, increased water filtration requirements, greater risk for drip emitter plugging, and potential for soil water logging when operated during cooler and wetter months. Recently, several manufacturers began developing modified drip products such as geotextile irrigation systems to deliver a band source of water and nutrients to the plants, rather than a point source produced by a standard drip system. A typical geotextile irrigation system has an impermeable base sheet or layer usually made of polyethylene or polypropylene, a drip line along that base, and a layer of geotextile fabric over top of the drip line. The geotextile material facilitates mass flow and disperses irrigation water and nutrients over a larger area than drip, which potentially increases the efficiency of water and fertilizer applications (i.e., less deep percolation and nutrient leaching) (Charlesworth and Muirhead, 2003; Devasirvatham, 2008; Miller et al., 2000). A wider, uniform wetting pattern may be particularly beneficial in shallow-rooted crops such as blueberry (Bryla and Strik, 2007). Furthermore, blueberry acquires primarily the ammonium (NH4) form of N (Claussen and Lenz, 1999), which is immobile in soil and, when applied by fertigation, decreases with distance and depth from the drip emitter (Haynes, 1990). The objective of the present study was to compare the effects of irrigation and fertigation with drip, microsprinklers, and geotextile tape on growth and early fruit production in northern highbush blueberry. Six cultivars were evaluated with each system, including, in order of ripening, Earliblue, Duke, Draper, Bluecrop, Elliott, and Aurora. Materials and Methods Study site. The study was conducted in a 0.27-ha field of northern highbush blueberry planted on 9–10 Oct. 2008 at the Oregon State University Lewis–Brown Horticultural Research Farm in Corvallis, OR (lat. 44 33#11$ N, long. 123 12#55$ W, 68 m elevation). Soil at the site is a Malabon silty clay loam (fine, mixed, superactive, mesic Pachic Ultic Argixerolls). The top 30 cm of soil contained an average of 2.4% organic matter, 32 ppm P (Bray I), 0.3 g·kg K, 2.2 g·kg Ca, 0.6 g·kg Mg, 0.3 mg·kg B, 31 mg·kg Mn, and 3 mg·kg Zn (tested by Brookside Laboratories Inc., New Bremen, OH). Soil pH was initially 6.2 but was adjusted to 5.5 (1:2 soil:water; Sept. 2008) by incorporating 670 kg·ha of elemental sulfur at 6 and 12 months before planting. The plants were obtained from a commercial nursery (Fall Creek Farm and Nursery, Lowell, OR) as 18-month-old container stock and transplanted 0.76-m apart on raised beds (0.4-m high · 0.9-m wide) at a density of 4385 plants/ha. The beds were constructed using a bed shaper and centered 3.0-m apart. HORTSCIENCE VOL. 50(6) JUNE 2015 897 | SOIL MANAGEMENT, FERTILIZATION, AND IRRIGATION