Nitrogen nutrition status of plants can be assessed either by direct or indirect tests. Direct tests consist in determination of total-N content in plant dry matter or N-O₃ content in green, indicator organs of the plants. Activity of nitrate reductase as well as the chlorophyll content in leaves are measured by indirect tests. Recently a fast and non-destructive chlorophyll measurement test with SPAD application is becoming more and more important.
Different methods used to evaluate the nutrition status of crops are described in the paper. Actually two groups of methods are distinguished: visual and chemical ones. The last ones include direct and indirect methods. Until now direct methods have had a dominant position. However, actually indirect methods become more and more popular mainly owing to their non-desfructive character and quick results they give. SPAD test based on measuring of chlorophyll contents is a good example of such a method.