| Nitrogen dosage and planting density are important factors affecting plant type and nutrient accumulation in flue-cured tobacco.This study was conducted in Pengshui County,Chongqing City,in 2021 using a field experiment with K326,the second largest flue-cured tobacco variety in the country in terms of planting area.Using a split plot design,two nitrogen application rates were set: 90 kg/hm2(N6)and 105kg/hm2(N7),and three planting densities were 1.52 × 104 plants/hm2(D55),1.67 × 104plants/hm2(D50)and 1.85 × 104 plants/hm2(D45)were used to study the effects of nitrogen application rate and planting density on the growth and development of leaves at different leaf positions,nutrient accumulation rules,dynamic changes in plant type,and yield and quality of flue-cured tobacco K326,with a view to providing references for improving plant type structure,coordinating nutrient absorption,and improving tobacco leaf usability.The main research results are as follows:(1)Increasing nitrogen fertilizer or reducing planting density significantly increased the plant height,stem circumference,leaf length,leaf width,leaf area,single leaf weight,leaf area coefficient,and leaf layer width of K326.At 75 days after transplanting,the plant height of N6D55 treatment was 82.30 cm,which was 3.65% and25.31% higher than that of N6D50 and N6D45 treatment,respectively;The plant height of treatment N7D45 was 29.28% higher than that of treatment N6D45;The leaf area coefficient of treatment N7D45 was 11.02% and 5.29% higher than that of treatment N7D55 and N7D50,respectively.(2)The maximum leaf area and dry matter accumulation of leaves decreased with the increase of nitrogen dosage.The leaves with the largest leaf area and dry matter accumulation of treatment N6D55 appeared at the 7th leaf position,while the leaves with the largest dry matter accumulation of treatment N7D55 appeared at the 6th leaf position;With the increase of planting density,the decrease in lower leaf area and dry matter accumulation was the largest,and the leaf position with the largest leaf area and the leaf position with the largest dry matter accumulation increased.Among them,the leaf position with the largest leaf area and the leaf position with the largest dry matter accumulation in treatment N6D55,N6D50,and N6D45 appeared at the 7th,8th,and 9th leaf positions,respectively.From 30 to 60 days after transplanting,both the maximum leaf area expansion rate and the maximum dry matter accumulation rate of the leaves appeared at the lower part of the plant;At the same nitrogen application rate,the maximum leaf area expansion rate first increased and then decreased with the increase of planting density.The maximum leaf area expansion rate of treatment N6D50 was25.70 cm2/d,which was 7.99% and 10.68% higher than that of treatment N6D55 and N6D45,respectively;The maximum expansion rate of leaf area did not change significantly when the nitrogen application rate was changed at the same planting density;Increasing nitrogen application rate or planting density promoted a decrease in the maximum rate of dry matter accumulation in leaves,with treatment N6D45 decreasing 12.22% and 0.56% compared to treatment N6D55 and N6D50,respectively,while treatment N7D55 decreased 3.03% compared to treatment N6D55.The angle between upper leaf stem and leaf decreased with the increase of nitrogen application rate,while the angle between lower leaf stem and leaf increased with the increase of nitrogen application rate;With the increase of planting density,the angle between stems and leaves first increases and then decreases.(3)Increasing nitrogen application rate and decreasing planting density both promote the increase of leaf layer width,while increasing planting density under low nitrogen treatment has no change in plant type.Under high nitrogen and medium density treatment,the plant type presents a dynamic change of long tube shape,high platform shape,and long tube shape,while under high nitrogen and high density treatment,the plant type presents a dynamic change of long tube shape,waist drum shape,and waist drum shape;The leaf layer width of flue-cured tobacco had a better fitting degree with the dry matter accumulation and leaf area of the leaves.(4)With the increase of planting density,the accumulation of nitrogen in the whole plant of K326 decreased,while the accumulation of potassium,calcium,magnesium,iron,manganese,boron,zinc,copper,and sodium in the whole plant first decreased and then increased;With the increase of nitrogen application rate,the accumulation of nitrogen,potassium,magnesium,iron,boron,and copper in the whole plant increased,while the accumulation of calcium in the whole plant decreased.With the increase of planting density,the accumulation of nitrogen in leaves,potassium and boron in lower leaves decreased;The accumulation of iron and sodium in leaves,phosphorus,zinc,and copper in middle and lower leaves,magnesium in lower leaves,calcium,manganese,and boron in middle leaves,and potassium,calcium,and magnesium in upper leaves decreased first and then increased.With the increase of nitrogen application,the accumulation of nitrogen in leaves,boron in lower leaves,and iron in upper leaves increased,while the accumulation of iron,manganese,and zinc in lower leaves,phosphorus,potassium,and calcium in middle leaves,and phosphorus,calcium,magnesium,and boron in upper leaves decreased.(5)With the increase of nitrogen application rate,the maximum accumulation of nitrogen,iron,and zinc in flue-cured tobacco K326 leaves increased at the leaf position,while the maximum accumulation of calcium in leaves decreased at the leaf position;With the increase of planting density,the maximum accumulation of potassium and manganese in leaves first decreased and then increased at leaf position,while the maximum accumulation of sodium in leaves first increased and then decreased at leaf position.The prediction degree of leaf dry matter accumulation on leaf calcium accumulation is better;The fitting degree of nutrient element accumulation in upper leaves and that in middle and lower leaves is better,and the prediction degree of nitrogen accumulation in upper leaves to that in lower leaves is the best,with R2 being0.922.(6)Increasing the planting density and nitrogen dosage significantly increased the yield of K326,but had no significant impact on the proportion of medium to top grade tobacco.The yield of treatment N7D45 was 7.98% and 1.36% higher than that of treatment N7D55 and N7D50,respectively,and the yield of treatment N7D45 was 0.53%higher than that of treatment N6D45.Increasing nitrogen application significantly increased the nicotine content of cured tobacco leaves.The nicotine content of treatment N7D45 was 3.20%,which was 44.14% higher than that of treatment N6D45.Increasing the planting density reduced the nicotine content of cured tobacco leaves,and the total sugar and reducing sugar content first increased and then decreased.The total sugar and reducing sugar content of treatment N7D50 were 33.51% and 27.76%,respectively,which were 8.45% and 14.81% higher than that of treatment N7D55,respectively.At a planting density of 1.67 ×104 plants/hm2,increasing the nitrogen application rate promoted the total sensory quality score.The total sensory score of N7D50 was 5.87,which was 1.21% higher than that of N6D50;With the increase of planting density,the total sensory score first increased and then decreased,and the total sensory score of treatment N6D50 was 0.35% and 0.87% higher than that of treatment N6D55 and N6D45,respectively.To sum up,the nitrogen application rate of flue-cured tobacco K326 is 105kg/hm2,and the planting density is 1.67 ×104 plants/hm2,the dynamic change of plant type was long tube shaped,waist drum shaped,and waist drum shaped.The growth and development of tobacco plants were good,and the quality of tobacco leaves was better. |
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