Effects Of Nitrogen Rates And Top-dressing Times On The Growth, Development And Quality Of Burley Tobacco

The effects of defferent nitrogen rates and top-dressing times on the growth, development and quality of burley tobacco were studied in Dazhou, Sichuan Province during 2007~2008. Simultaneously, dynamics of soil nutrients, dry matter, total nitrogen, nicotine in burley tobacco were investageted. The main conclusions were as follows:(1) The contents of soil alkalytic nitrogen (AN), available phosphorous (AP) and available potassium (AK) increased rapidly at the 30th day after transplanting. During rapid growing stage, the content of AN decreased gradually, then increased at the 60th day after transplanting. The increasing amplitudes were quite high in the treatments with higher nitrogen rates and later top-dressing time. The contents of AP and AK decreased rapidly after transplanting 30d~60d, and decreased more rapidly with the increasing of nitrogen application rate. At the same nitrogen application rate, the changes of the contents of AP and AK in soil were comparatively slight in the later top-dressing time treatment .(2) Plant height, stem girth, leaf area and effective leaves increased with the increment of nitrogen rates and the delay of top-dressing time. However, top-dressing had adverse effect on timingly harvesting when the amount of nitrogen fertilizer was over 225 kg/hm2.(3) The accumulation trend for dry matter presented the rule of"slow-fast-slow"duing the process of growth and development. The amount and rate of dry matter accumulation increased with the increment of nitrogen fertilizer application rate. The accumulation of dry matter for tobacco in early stage were inhibited when the amount of nitrogen fertilizer exceeded 225 kg/hm2. Postponing top-dressing time was benefit to the accumulation of dry matter. However, when the amount of nitrogen was lower than 165kg/hm2, postponing top-dressing time had no good for dry matter accumulation. The dry matter accumulation rates of different tobacco varieties were also different. The dry matter accumulation rate of early ripening variety decreased after transplanting 60d, and the late ripening variety had a high accumulation rate still.(4) The content of total nitrogen in tobacco leaves decreased with the advancing of growth process, but the extent of decrement slowed down with the increment of nitrogen application rate and the postponing of top-dressing time. The content of nicotine increased with the advancing of growth process, presenting a maximum value at the 75th day after transplanting. The speed of nicotine accumulation in treatment with top-dressing was slower in early stage, and then speeded up with the advancing of growth process. The treatments with later top-dressing time had high content of nicotine at harvesting time.(5) The yield and output value of burly tobacco increased with the increment of nitrogen application rate, but the output value decreased when the amount of nitrogen application exceeded 195kg/hm2 for early variety and 225kg/hm2 for late variety. The yield and output value could be increaded by postponing top-dressing time with same nitrogen application rate.Nitrogen rata and top-dressing time had great effect on appearance quality, smoking quality and chemical components as well as mineral elements of cured tobacco leaves. The content of oil, body and luster of cured tobacco leaves gradually reinforced along with the increment of nitrogen application rate and the postponing of top-dressing time. However, the luster of cured leaves tarnished in the application amount of nitrogen over 225kg/hm2.With the raise of nitrogen and the postponing of dressing time, the style of cured leaves was more significant, physiological strength, whereas the volume of aroma and taste concentration became strong. However, offensive odor and biting taste increased, and after-taste became uncomfortable.The chemical components in different stalk position tobacco leaves changed greatly, whele the content of total suger and reducing suger presented: cutter>upper>lower leaves. The content of The total nitrogen and nicotine and K+ increased with the raise of stalk position. With the increment of nitrogen level and the postponing of dressing time, the content of total nitrogen, nicotine and K+ increased, while the content of total sugar and reducing suger decreaced.The content of P,K,B,Mn in tobacco leaves increased with the increment of nitrogen rate and the postponing of dressing time, but the content of Ca,Mg,Fe,Cu,Zn decreased(6) The contents of phenylalanine, products of browing reaction, carotenoid and neophytadiene in tobaccos were increased with the increment of nitrogen application rate and the postponing of top-dressing time, but the content of all kinds of aroma-active components decreased when the application amount of nitrogen exceeded 225kg/hm2 .The postponing top-dressing intensified the decrement of aroma-active components in tobacces. The content of products of browing reaction in treatments with later top-dressing time was higher than that of early top-dressing treatments and CK at 225kg/hm2 nitrogen application level.