Efficiency of Nitrogen Fertilizer Use by Shade Tobacco Improved by Timed Applications1

Abstract

AbstractShade‐grown cigar wrapper tobacco (Nicotiana tabacumcv. ACC‐75) is fertilized annually with large amounts of organic N with little regard for residual N from previous crops. The potential for leaching of nitrate and consequent groundwater pollution can be high. In 1980, shade tobacco plants grown in Merrimac sandy loam (Entic Haplorthods) and fertilized with 67,134, and 202 kg ha−1of N, supplied as Ca(N03)2metered through overhead irrigation in small portions throughout the growing season, were compared with plants receiving a conventional organic N treatment of 252 kg ha−1. These plants had different N uptake patterns, but similar total N content at the end of the season. In 1982, Ca(N03)2was metered at 179 and 224 kg ha−1of N in amounts determined by the average N uptake over time in 1980 and compared with a conventionally fertilized organic source (224 kg ha−1of N) and with a treatment receiving no N. While total leaf yields for plots receiving no N were considerably lower than those receiving N, their N uptake closely matched the other treatments for about 45 days after transplanting, suggesting that residual N in the soil is available for plant growth early in the season. One treatment in 1983 was designed to utilize this residual N as a part of a metered program applying a total of only 140 kg ha−1of N. Leaf yields from this treatment were not significantly different from those receiving 224 kg ha−1of conventional N. These timed fertilization treatments reduced the potential for leaching of nitrate while not affecting leaf harvest yields.