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A critical assessment of the value of petiole sap analysis in optimizing the nitrogen nutrition of the potato crop

D.K.L. MacKerron, M.W. Young and H.V. Davies
Plant and Soil
Vol. 172, No. 2 (May (II) 1995), pp. 247-260
Published by: Springer
Stable URL: http://www.jstor.org/stable/42947485
Page Count: 14
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A critical assessment of the value of petiole sap analysis in optimizing the nitrogen nutrition of the potato crop
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Abstract

The importance of standardizing on sampling procedures was shown by examining diurnal variation of petiole sap nitrate-N concentration, [$NO_3^-$], and its variation within the plant. There was important variability in petiole sap [$NO_3^-$-N] about the general decline in values through the season, in time, between cultivars, between nitrogen fertilizer treatments, and between replicates. We have shown the lack of a consistent relation between petiole sap [$NO_3^-$-N] and rates of uptake of nitrogen either in the period around the time of sampling, or integrated over the whole growing season. Finally, we have examined the literature and have been unable to find reports of critical, independent tests of the use of petiole sap [$NO_3^-$] to guide the application of fertilizer supplements. We conclude that a new, critical attitude should be taken to testing petiole sap [$NO_3^-$] if the technique is to be used properly and to its seeming potential. Comparisons were made between measurements using a hand-held system and an auto-analyser.

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