Evaluation of Nitrogen Sources and Rates on Yield and Quality of Modern Flue-Cured Tobacco Cultivars

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Title: Evaluation of Nitrogen Sources and Rates on Yield and Quality of Modern Flue-Cured Tobacco Cultivars
Author: Parker, Robert Gary
Advisors: Michael Wagger, Committee Member
Randy Wells, Committee Member
W. David Smith, Committee Co-Chair
Loren Fisher, Committee Co-Chair
Abstract: Nitrogen has a more pronounced effect on the growth and quality of tobacco than any other essential element even though it is not taken up in the highest quantity. Soil nitrogen regime affects plant development more than any other nutrient from seedling stage through the time of final harvest. The role of nitrogen in the development and quality of tobacco is of major importance with respect to time of absorption, form of nitrogen absorbed, rate of application, concentration in the leaf and numerous other aspects. Soil nitrogen must be sufficient during early and mid-season growth stages to ensure vigorous, but not excessive growth, and it should be nearly depleted by flowering for the plant to mature and ripen properly insuring a quality leaf. In general, as total N in the plant increases, above the amount required for maximum growth, quality of flue-cured tobacco tends to decrease. Field studies were conducted at two locations in both 2006 and in 2007 to evaluate response to nitrogen rates. Cultivars NC 71 and K 346 were selected for this study based on differences in the North Carolina Official Variety Test, with NC 71 averaging greater than 450 kg/ha more yield than K 346. Also, it has been observed that K 346 has a lower quality index than NC 71 when both varieties are produced using similar rates of nitrogen. Calcium nitrate was used as the total source of nitrogen and rates used were 45, 56, 67, 78, and 90 kg of nitrogen per hectare. Nitrogen was split applied with one half of the total applied within the first week after transplanting and the balance applied approximately 14 days later. All other production practices followed standard practices for the individual research station. There were significant main effects for variety. NC 71 averaged 3175 kg/ha while K 346 averaged 2798. There were no differences between varieties for grade index or dollars per kilogram. Dollars per hectare followed the same trend as yield with NC 71 grossing $1,247 dollars more per hectare than K 346. The main effect for nitrogen rate was also significant. Yield and dollars per hectare increased as nitrogen rate increased up to 78 kg of nitrogen per hectare. Total alkaloids increased as nitrogen increased and total reducing sugars decreased. Although yield between the cultivars was different the trends were the same with response to nitrogen. As the nitrogen rate increased, yield for both cultivars increased with no negative affect on quality. Therefore, K 346 requires the same rate of nitrogen to achieve maximum yield as NC 71 even though there was a significant difference in yield between the two cultivars. Studies were conducted at one location in 2006 and two locations in 2007 in order to determine if fertilization with urea or urea plus Agrotain (urease inhibitor) would produce flue-cured tobacco similar to that obtained from a nitrogen regime of all nitrate nitrogen. Treatments consisted of three sources of nitrogen: calcium nitrate, urea, and urea plus Agrotain and applied at rates to provide 56 and 78 kg of nitrogen per hectare. Nitrogen source did not affect yield, grade index, dollars per kilogram or total reducing sugars. However, nitrogen source did affect total value and total alkaloids. Increasing the nitrogen rate from 56 to 78 kg/ha increased dollars per hectare by $417 and increased total alkaloids from 3.46 to 3.67 percent. Calcium nitrate produced a higher return per hectare than did urea or urea plus Agrotain. Rainfall was normal for 2006 but was lower than normal for 2007, which could have slowed the rate of nitrification. From these experiments we conclude that urea or urea plus Agrotain will not produce flue-cured tobacco of equal value or similar alkaloid levels as an all nitrate regime under the environmental conditions. Field studies were conducted at two locations in 2004, 2005, and 2006 to evaluate sources and rates of nitrogen for the production of flue-cured tobacco. Calcium nitrate, ammonium nitrate, and urea ammonium nitrate (UAN) were evaluated. Sources were chosen based on previous research that provided inconsistent results when using ammonium nitrate and UAN for flue-cured production. The rates of nitrogen evaluated were 0, 22, 45, 67, and 90 kg N/ha in all years with 112 and 134 kg N/ha rates added in 2005 and 2006. All treatments received 134 kg of potassium per hectare within seven days of transplanting. Nitrogen application was applied twice with one-half of the total applied within the first week after transplanting and the balance applied approximately 14 days later. All other production practices followed standard practices for the individual research stations. Nitrogen source did not affect yield, grade index, value, total alkaloids, total reducing sugars, or leaf color. Yield increased at all locations as nitrogen rate increased up to 67 kg/ha. Yield decreased at nitrogen rate above 90 kg/ha. Dollars per hectare followed the same trends as yield since grade index was not affected by nitrogen rate. Total alkaloids increased as nitrogen rate increased up to 112 kg N/ha. Inversely, total reducing sugars decreased as nitrogen rate increased. Leaf color in the field increased as nitrogen rate increased. Soil nitrate levels increased at the highest level of nitrogen tested at both topping and final harvest sampling times. Nitrate levels at two intervals for treatments receiving 134 kg N/ha were almost double that of any other treatment tested. Ammonium levels were higher, at topping, in the top 15-cm soil samples when UAN was applied. At final harvest, soil nitrate levels were higher, in the upper 30-cm, for treatments receiving calcium nitrate.
Date: 2009-03-24
Degree: PhD
Discipline: Crop Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/5711


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