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A petiole sap test for nitrate and potassium in Sultana grapevines
Author(s) -
NAGARAJAH S.
Publication year - 1999
Publication title -
australian journal of grape and wine research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.65
H-Index - 77
eISSN - 1755-0238
pISSN - 1322-7130
DOI - 10.1111/j.1755-0238.1999.tb00152.x
Subject(s) - petiole (insect anatomy) , vineyard , potassium , nitrate , horticulture , nutrient , zoology , potassium nitrate , chemistry , diurnal temperature variation , botany , dry weight , agronomy , biology , hymenoptera , organic chemistry , atmospheric sciences , geology
A sap test has been developed to measure petiole nitrate and potassium concentrations in Sultana grapevines. Sap extraction was carried out after freezing the petioles to cause cell rupture. The thawed samples were macerated along with water in a blender. Merck RQflex(r) test strips were used to measure nutrient levels and the test strip colour intensity was measured using the RQflex reflectometer. The accuracy of the sap test was checked against conventional analysis and found to be satisfactory. Considerable variation in nitrate and potassium concentrations were observed in petiole samples collected in a vineyard. More studies are needed to determine the number of petioles that must be collected for the sap test. In the meantime, it is tentatively suggested that at least 200 petioles be collected for the sap test. Nitrate and potassium concentrations showed slight non‐uniform diurnal variations between 0800 h and 1600 h (Eastern Summer Time). The effect of diurnal nutrient variations on the test results may be reduced by collecting petioles between 0800 h and 0930 h. The petiole dry weight percent increased from about 6 to 12% during the season. This change should be taken into account when sap test results are converted from fresh to dry weight basis.