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  • P solubility diagram  (1)
  • nitrogen fertilization  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Orthophosphate solubility in waters of different ionic composition (1995)
    Springer
    Nutrient cycling in agroecosystems 44 (1995), S. 73-78 
    Details
    ISSN: 1573-0867
    Keywords: P precipitation ; precipitation kinetics ; P solubility diagram ; pH ; octacalcium phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Orthophosphate (OP) is a major component of irrigation and nutrient solutions. Since OP precipitates may clog drippers, and deviations from intended OP concentrations may adversely affect plant development and yield, an understanding of the mechanisms controlling OP solubility in solutions of various ionic compositions, is essential. The objectives of this study were (i) to suggest guidelines for permitted OP additions to waters of various ionic compositions, so as to avoid OP crystallization and (ii) to predict the decrease in OP concentration as a function of time in supersaturated solutions. Five freshwater sources, used for irrigation in Israel, and representing extremes of pH and of Ca, HCO3 and SO4 concentrations, were tested. Solutions of three different initial OP concentrations (10, 30 and 90 mg Pl−1) and two pH values were prepared in 21 plastic bottles and kept in a dark room at 27 °C. Solution samples were withdrawn from the bottles at predetermined times, filtered and analysed for pH and total OP, Ca and HCO3 concentrations. In all the studied waters and for all initial OP levels the OP concentration (Cp) declined with time. The rate of decrease in Cp was proportional to the difference between the observed and equilibrium Cp values, with a specific rate constant for each water.The pH and the Ca2+ and HCO 3 − activities in solution were influenced by the initial Cp. The equilibrium Cp in all treatments was found to be controlled by octacalcium phosphate (OCP). Available chemical equilibria models allow to calculate the maximum level of OP that can be added to various waters before OCP precipitates, based on water pH and Ca, HCO3 and SO 4 2− concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750694
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  • 2
    Electronic Resource
    Electronic Resource
    Drip nitrogen fertigation of ‘Starking Delicious’ apple trees (1989)
    Springer
    Plant and soil 119 (1989), S. 305-314 
    Details
    ISSN: 1573-5036
    Keywords: chlorophyll ; fruit size ; harvest date ; leaf analysis ; nitrogen fertilization ; soil analysis ; spur ; vegetative growth ; yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The response of ‘Starking Delicious’ (Malus domestica Borkh.) apple trees to four N fertigation treatments in drip irrigation (50, 150, 250 and 400 kg N ha−1, supplemented with a uniform dose of 400 kg K ha−1) was investigated in a field experiment during 6 years. Nitrate nitrogen in the soil was proportional (7–58 mg kg−1) to the applied N dose at the end of a 6 week fertigation period in the spring. At other times, the nitrate concentration in the soil was very low. Soil K decreased with depth and in the 0–30 cm soil layer it was negatively correlated with the applied N dose, before fertigation started. At the end of the spring fertigation period, higher K was found in all soil layers analyzed. Vegetative growth was correlated positively with the amount of N applied. Leaf chlorophyll and N were significantly lower only in the lowest N treatment, while increased fruit size and decreased fruit color were measured only in the higher N treatments. Yield was severely biennial. In the ‘On’ years crop load was heavier as less N was applied. An extremely high crop load in the lowest N treatment was followed by a reduced flower density and yield in the following season. In the ‘Off’ years, a significantly higher yield was obtained with the 150 kg ha−1 dose. The dry weights, N, P and K contents of the above ground parts of mature apple trees were determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370423
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