Determination of Nitrogen Status in Winter Wheat by Measuring Basal Stem Tissue Sap Nitrate Concentration
The aim of this study was to assess a quick-test method determining nitrate in basal stem tissue sap for the prediction of nitrogen status in winter wheat (Triticum aestivum L.). The nitrate content in plant stem tissue sap collected at Zadoks growth stages GS 31 and GS 49 of winter wheat in 11 annual field trials in south-east Norway in the years 1993-96 was measured with Merckoquant test strips with a Nitracheck Meter. Relationships between NO3- concentrations and final yields were good within individual trials, but when the results from all trials were pooled, the NO3- concentration was a poor predictor of final yields. This study suggests that the critical nitrate values required in plant stem sap for sufficient grain protein content for bread-baking quality are 4000 ppm NO3- at GS 31 and 2000 ppm at GS 49 in situations with a single N application in the spring. In situations with split N applications (25 kg N ha-1 at GS 31 and 25 kg N ha-1 at GS 49 in addition to spring application), 1000 and 500 ppm were found to be the critical values at GS 31 and 49, respectively. Because of the large between-site and between-year variability, this study does not indicate that the method can be recommended for extended practical use.