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  • Author or Editor: D. C. Cosgrove x
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Abstract

A shift in the form of Ν in the nutrient solution to all NH4 after initial bloom significantly reduced pod yield as much as 50%, depending on the prebloom NO3/NH4 ratio. Pod yield was unaffected by prebloom NO3/NH4 ratio if at least half of the Ν in the nutrient solution was NO3, or if NO3 supplied all of the Ν during postbloom development. Therefore, for maximum pod yield, NO3 should be the primary Ν form supplied to snapbean plants after bloom. Kjeldahl Ν values were consistently high in the vegetative tissue with NH4 as the predominant Ν form, indicating that the use of Kjeldahl Ν values as an indicator of the Ν status of the plant in relationship to pod yield would be a misuse of this diagnostic tool without knowing the predominant Ν form being absorbed by the plant. The NO3 content in upper mature leaves at pod maturity was significantly correlated (r = 0.88***) to NO3 level applied, with a value of 7000 ppm in the leaves associated with highest pod yield. Total Ν (Kjeldahl Ν + NO3) of at least 5.50% in upper mature leaves at pod maturity was associated with highest pod yield.

Open Access