Whole Leaves Versus Petioles for Assessing the Nitrogen Status of Tomatoes

Tomatoes ( Lycopersicon esculentum Mill.) were sampled for laboratory analysis of nitrate nitrogen (NO 3 -N) in one greenhouse and four field experiments. A ratio of about 3:1 (petiole NO 3 -N to whole leaf NO 3 -N) was found over a wide range of conditions for the third leaf below the growing tip and leaves further below this point. The ratio was higher for the very youngest leaves. Nitrate-N increased with leaf age and then remained relatively constant. Whole leaves proved just as effective as petioles for reflecting changes in available N.