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Fluid Journal : Fluid Journal 2005-2007
Spring 2006 FLUID JOURNAL Page 2 acidification and correct K deficiency via fertigation. Inadequate leaf micronutrient concentrations have also been observed for high-density orchards receiving macronutrient fertigation, implying that strategies for maintenance of micronutrient nutrition are also important for these production systems. Micronutrient deficiencies, including B, have long been reported to potentially cause major growth problems for apples grown in traditional orchards of this region. The objective of this study was to assess the effectiveness of fertigation to supply B for apple trees already receiving N and K via fertigation. B management helps Five years of N and K fertigation treatments tended to decrease leaf B concentrations with significant decreases observed as rate of fertigated N increased in 1992 and 1995, plus the addition of K fertigation the last three fruiting years (1994 to 1996). These relative decreases in leaf B concentration likely resulted from dilution due to growth stimulation, especially by K fertigation. Cultivar consistently affected leaf B concentration with highest annual leaf B concentrations measured for 'Fuji' and 'Spartan' cultivars from 1994 to 1996 (Figure 1). Boron nutrition was managed differently throughout the study with no B applications in the first two years. In 1992, leaf B concentrations were generally low to adequate, regardless of cultivar, and by 1993 leaf concentrations were near or below 20 ppm (Figure 1), considered a deficiency threshold for apple. Susceptibility toward B deficiency has long been recognized in orchards of the semi-arid, fruit growing region of the Pacific Northwest where B additions via organic matter mineralization or precipitation are minimal. These results confirm a recent survey of drip-irrigated and NP-fertigated apple orchards that found possibly deficient leaf B concentrations in more than half of the surveyed locations. Leaf B deficiency occurred rapidly within two years in our research study on a sandy soil, paralleling the situation in grower orchards where problems occurred after only two to five years of NP fertigation, and where lowest extractable soil B values were measured in orchard soils with a high content of sand. In the spring of 1994, classic B deficiency symptoms were observed as 'blossom blast' on a small percentage of flowers on all cultivars but not on all trees throughout the experimental block (Figure 2). This disorder involves drying and shriveling of flowers at bloom and is distinguishable from frost damage by the longer retention time of the damaged tissue on the tree. Two foliar B sprays were subsequently applied in early May and mid-June, resulting in contaminated leaves and high leaf B concentrations by mid- summer of 1994 (Figure 1). Maintenance of B nutrition by foliar sprays is a standard commercial recommendation in interior British Columbia orchards and was apparently Figure 2. 'Blossom blast' symptoms (indicated by dashed box) as ob- served in spring of 1994 on apple trees in the experimental block. Figure 3. Soil solution concentration of B as influenced by fertigation for 0.34 g B tree in 1995 and 1996.
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