Nitrogen rate and cultivar effects on nitrogen and nitrate concentration of sweet potato leaf tissue

The effects of 4 ? application levels, 0, 45, 90, and 135 kg N/ha, and 2 cultivars, ‘Centennial’ and ‘Jewel’, on total ? and NO3‐N concentration of leaf blades and NO3‐N concentration of petioles were determined in 2 field experiments. The concentrations of NO3‐N in petioles of ‘Centennial’ plants were much higher than those of ‘Jewel’ plants. Petiole NO3‐N concentrations were more sensitive to differences in soil ? application levels than blade total ? concentrations. Petiole NO3‐N concentrations were also affected by plant age at sampling. While petiole NO3‐N concentration was a reliable indicator of current ? status of the plants, total ? concentration of blades appeared to be a more reliable predictor of yield. Critical concentrations of total ? in blades associated with a 5% reduction in total marketable root yield were 3.0 and 3.2% for ‘Centennial’ and ‘Jewel’, respectively.