Nitrogen Status Evaluation of Tomato Plants1

Recently matured whole leaves of tomato Lycopersicon esculentum Mill cvs. Centennial and Knox) gave the most reliable indication of total N, while NO 3 -N in older mature leaf petioles better reflected N availability and absorption. The NO 3 -N content of petioles was more indicative of N status of the plant than total N analysis of whole leaves. The NO 3 -N and total N contents of leaf parts generally decreased with increasing maturity. Soil solution NO 3 -N concentration increased exponentially with increasing N application rates. The first 45 kg N/ha increments increased soil solution NO 3 -N concentration only 10 ppm whereas the fourth 45 kg N/ha increment increased NO 3 -N concentration 40 ppm. Ninety kg N/ha application produced a concentration of 48 ppm NO 3 -N that resulted in a nearly maximum petiole concentration of 14,500 ppm NO 3 -N, indicating that this NO 3 -N concentration provided sufficient available N for the immediate reserve requirements for plant growth.