RELIABILITY OF PETIOLE SAP TEST FOR N NUTRITIONAL STATUS ASSESSING IN PROCESSING TOMATO

A field experiment was carried out in Central Italy to assess the reliability of petiole sap for determining nitrogen (N) status on processing tomato. The crop was fertilized with different N rates and fertigation-irrigation frequencies. Reduced-N and nitrate-N concentrations were determined by lab analyses at 30, 42, 57, 71, and 84days after transplanting. At each sampling date, the assessment of N nutritional status as resulted by sap test was compared with the actual plant N status as determined by nitrogen nutrition index (NNI). Results from sap test were in agreement with NNI indications for about 2/3 of crop cycle that represents the crucial time for N fertilizer management in tomato. The correlation coefficient of the two methods was, on average 0.854 and it was statistical significant in the whole sampling period. The nitrate concentration in the petiole sap provided a good agreement with laboratory analysis across the full range on N-nitrate (NO3) concentrations examined.