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Experiments conducted since 1986 indicate that multi-nutrient fertigation may be effective in improving early growth and yield of new orchards. However, the early studies did not provide information concerning the contributions of individual nutrient elements to these responses. Experiments were established in 1993 and 1994 to compare effectiveness of alternative sources, rates, and methods of applying K, Zn, and Cu through drip irrigation compared with annual soil surface applications to `McIntosh'/M.9 and `Empire'/M.9 trees. After 3 years, leaf K, cumulative shoot growth, and first crop year yields were increased by application of K. Differences between sources, rates, times, or methods of application generally were not significant when relatively high rates were applied. However, early results from a rate study indicate a significant K source by rate interaction. Soil surface application of K plus drip irrigation appears to be comparable to fertigation in supplying this element. After 2 years, applying EDTA chelates of Zn and Cu through fertigation increased leaf Zn and Cu, respectively, but high rates required are considered to be uneconomical when compared with foliar sprays of these elements.
Fertilizer treatments were applied by spreading over an herbicide-treated in-row strip, with or without irrigation using single-drip emitters per tree, or through drip irrigation. Distribution of nutrients in soils was evaluated by analysis of soil samples collected at various depths and distances from the irrigation emitters at the end of the 8-year experimental period. NO3-N was increased in the 0- to 40-cm depth by soil surface application but below 40 cm with fertigation. Fertigation increased P in the wetted zone within the 0- to 40-cm depths. Surface application of K increased levels primarily in the 0- to 20-cm zone, while fertigation increased K to depths of 80 cm. Zinc and Cu concentrations were increased by fertigation to 80-cm depth. In general, nutrients applied to the soil surface were less readily moved into the soil profile, while fertigation resulted in greater movement of nutrients to greater depths within the wetted zone of soil.
Species of Phytophthora are serious soilborne pathogens of persian (english) walnut, causing crown and root rot and associated production losses worldwide. To facilitate the development of improved walnut rootstocks, we examined resistance of 48 diverse clones and seedlings of Juglans species to P. cinnamomi and P. citricola. Plants were micropropagated, acclimatized to a greenhouse environment, and then exposed to the pathogens in artificially infested potting soil mix. Inoculated plants, as well as noninoculated controls, were subjected to soil flooding for 48 hours every 2 weeks to facilitate infection by the pathogens. Two to 3 months after inoculation, resistance to the pathogens was assessed according to the severity of crown and root rot. Clonal hybrids of J. californica × J. regia were highly susceptible to the pathogens (means 52% to 76% root crown length rotted), while several clones of J. microcarpa × J. regia were significantly less susceptible (means 8% to 79% crown length rotted). Among clones of other parentages tested, including: J. microcarpa, (J. californica × J. nigra) × J. regia, J. hindsii × J. regia, (J. hindsii × J. regia) × J. regia, [(J. major × J. hindsii) × J. nigra] × J. regia, and J. nigra × J. regia, responses varied, but tended to be intermediate. When ‘Serr’ scions were budded or grafted on J. microcarpa × J. regia clone ‘RX1’ or Paradox (J. hindsii × J. regia) seedling rootstocks in a commercial orchard infested with P. cinnamomi, all trees on ‘RX1’ remained healthy, whereas only 49% of those on Paradox survived. Thus, useful resistance to Phytophthora is available among J. microcarpa × J. regia hybrids and is evident in ‘RX1’ rootstock.