Nitrogen Requirements for Flue‐Cured Tobacco

Fertilizer N excesses may have negative effects on both crop and water quality. To reduce the risk of N excesses it is essential to accurately define fertilizer N rates. The estimate of the most suitable N rate is complicated by the fact that a certain amount of the N taken up by the crop during the growth season is supplied by the soil. The aim of this work was to estimate the amount of N that can become available for plant uptake during the crop growth season. The effects of five N rates (0, 20, 40, 60, and 80 kg N ha−1) on production traits of flue‐cured tobacco (Nicotiana tabacum L.) cv. K326, and on selected items of an N balance applied to the soil–plant system were studied on a loam soil, in 1998 and 1999, at Bovolone (Verona, northern Italy). The fertilizer N rate positively and significantly influenced cured‐leaf yields only in 1999, whereas the time to harvest increased linearly for increasing N rates, in both years (0.25 d on average for every further kg of fertilizer N). The N balance indicated a remarkable reduction of the soil organic N stock and an increase of the soil inorganic N levels throughout the crop growth period. As these changes were both proportional to the fertilizer N rate, the occurrence of a positive priming effect was hypothesized. The formulation of N fertilizer recommendations to farmers should take into account the existence of priming effect phenomena.