Nutrient absorption nitrates

As an example, the data from Ketchum (37) for the rate of phosphate absorption as a function of both phosphate and nitrate concentration can be satisfactorily fit with a product of two Michaelis-Menton expressions. The resulting fit, obtained by a multiple nonlinear regression analysis, is shown in Figure 5. The Michaelis constants that result are 28.4 p.g NOa-N/liter and 30.3 pg P04-P/liter, with a saturated absorption rate of 15.1 X 10 8 pg P04-P/cell-hr. This approximation to the growth rate behavior as a function of more than one nutrient must be regarded as only a first approximation, however, since the complex interaction reported between the nutrients is neglected. 

Basic sulfates of zinc and manganese are used as minor-element nutrient sprays as well as for fungicidal purposes, with or without copper. Basic phosphates also are employed. All of these salts generally are prepared under controlled-pH conditions (sometimes in situ in the field) in such a way that a fairly insoluble salt is provided. Thus, its solubility limited the quantity of soluble metal ion available at any given time for absorption by the plant. The high quantities of Zn" Cu" and so on, that would be obtained from the normal sulfate, nitrate, or halide sprays would be too phytotoxic for practical use. 

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