Diagnosing nitrogen fertilization requirements of cereals in less than 30 seconds

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Abstract
Stems of barley and wheat plants of wide range in nutritional status were analysed for sap NO3 concentration at the tillering stage using both "Merckoquant" nitrate test strips and a specific-ion nitrate electrode. Even though the "Merckoquant" test strips used in this study did not give precise NO3 readings they were found to be a satisfactory method for determining the NO3 content of stems of cereals, and can be used in situ by farmers to predict the necessity of N fertilization for maximum grain yield. If the NO3 sensitive area on the test strip is coloured to match the standard 500 ppm NO3 colour in less than 30 seconds, after the application of sap, this is an indication of adequate N nutrition. If the 500 ppm NO3 colour standard is reached between 30 to 60 seconds, then this is an indication of intermediate N nutrition and fertilization is recommended only under favorable weather conditions. If colour development of the test strip for the 500 ppm NO3 standard takes more than 60 seconds, or the colour developed does not reach this standard, this is an indication of deficient N nutrition. Therefore, the use of the "Merchoquant" test strips offers a useful tool in deciding if N fertilization of small-grain cereals is needed.