NITRATE MEASUREMENTS IN PROCESSING TOMATO LEAVES BY A QUICK TEST

In two plots of a field of processing tomato cv Brigade grown with a nitrogen (N) fertilization equal to 110 kg N ha^‑1 or to 298 kg N ha^‑1 the leaf NO₃-N concentration was estimated in recently mature leaf samples collected every week, for twelve weeks, by a quick test (QT) in fresh material and also in the same samples by the ion chromatography (CH) method after drying and grinding. The NO₃-N concentration in the dry matter of petioles measured by QT (NO₃-N)_QT ranged from 74 to 5584 mg kg^‑1 and from 202 to 5924 mg kg^‑1 dm in the low N and high N treatments, respectively, while the concentration of NO₃-N measured by CH (NO₃-N)_CH ranged from 262 to 10518 and from 657 to 15405 mg kg^‑1 in the low N and high N treatments, respectively. The values of NO₃-N in petioles and blades decreased over the crop development according to typical data from literature. Petioles gave a closer correlation (higher R²) between (NO₃-N)_QT and (NO₃-N)_CH than the blades and thus could be considered as better indicator plant part for shoot nitrate content evaluation. The linear regression between the NO₃-N values measured by the QT and the CH in all the analysed plant samples (n=48) resulted in the linear relationship: (NO₃-N)_QT=0.44*(NO₃-N)_CH+17.75 with R²=0.93.