Effect of Urea on Yield and Quality of Flue-cured Tobacco1
- Linda MacKay Williams and
- G. S. Miner2
Flue-cured tobacco (Nicotiana tabacum L.) can be sensitive to NH+4-N in the soil, especially in the presence of CI−. Nitrogen sources such as (NH4)2SO4 and ammonium phosphates have depressed growth in the presence of strong, general-purpose fumigants containing CI− that are sometimes used in tobacco culture, but little information is available for urea under similar conditions. Thus, urea was compared to NaNO3 in eight field experiments to evaluate the interactive effects of N sources and fumigants on the growth and chemical composition of flue-cured tobacco. The various soils are listed in the Materials & Methods Section.
Urea and NaNO3 were applied singly or combined to provide four combinations of NO−3-N and NH+4-N in 1976 and 1977 and three combinations in 1978. Nitrogen was applied at 67 kg/ha except for an extra level of 112 kg/ha from urea in 1978. Fertilizers were banded in nonfumigated soil and soil treated with recommended rates of MoCap [O-Ethyl S, S-dipropyl phosphorodithioate] and Telone C-17 [dichloropropylene, trichloronitromethane] in 1976 or Terr-0-Cide 30 [ethylene dibromide, trichloronitromethanel and Telone C-17 in 1977 and 1978.
Yield and grade index were increased 26 and 20%, respectively, by urea compared to NaNO3 when excess rainfall occurred shortly after planting. Apparently, N from urea was still present as NH+4-N and remained within the root zones while N from NaNO3 moved below the root zone. In a dry year, urea resulted in a 7% Under conditions of adequate and well-distributed rainfall, both N sources had similar effects on tobacco.
From 4 to 6 weeks were required to complete nitrification, depending on year and location, and the extent of nitrification at 2 and 4 weeks was reduced by both Terr-0-Cide 30 and Telone C-17 compared to nonfumigated soil. Chloride concentrations in leaves increased until the 6th week and then abruptly declined, coinciding with the disappearance of NH+4-N. Leaf CI− levels as high as 3.5% at 6 weeks were obtained for urea in the presence of Telone C-17 but they were less than 0.5% in cured leaves at harvest, irrespective of N source or soil chemical treatment.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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