Effects Of Different Available P Levels On Soil Phosphorus Forms,Yield And Quality Of Flue-Cured Tobacco

In tobacco production,the long-term large-scale application of phosphorus fertilizer leads to rapid enrichment of phosphorus in soil,Excessive application of phosphorus fertilizer not only reduces the yield and quality of tobacco leaves and the utilization rate of phosphorus fertilizer,but also may cause environmental problems.Based on this,this study firstly analyzed the distribution of phosphorus content and phosphorus form in tobacco-growing soil in Enshi through a large number of sampling survey,and initially revealed the effect of phosphorus enrichment on flue-cured tobacco quality.Secondly,the culture experimentswere carried out to study the effects of different soil available P levels on flue-cured tobacco yield and quality.Finally,two-year field experiments were carried out to research the suitable application amount of phosphorus fertilizer in phosphorus enriched soil with different phosphorus application levels,in order to provide theoretical basis for rational application of phosphorus fertilizer in phosphorus enriched tobacco planting soil in Enshi.The main results obtained as follows:（1）The investigation results showed that the average available P content of tobacco-growing soil was 67.95 mg/kg,and the available P content higher than 50.00mg/kg was arrived at 68.13%of all samples.The main soil P form was Na OH-P（38.45%）,followed by Na HCO₃-P（26.56%）and residual P（21.81%）,and the last were HCl-P（10.22%）and H₂O-P（2.96%）.The active P（H₂O-P and Na HCO₃-P）was 29.52%,while the medium active P（Na OH-P）and stable P（HCl-P and residual P）was 70.48%.Great influence was found between soil p H value and organic matter content and P form.Soil acidification increased the Na OH-P content,but decreased the HCl-P content,however,the improvement of organic matter increased the soil organic P content.the improvement of soil available P content could increase all kinds increased content.Compared with before planting flue-cured tobacco,the content of active P decreased after planting flue-cured tobacco,while the content of medium active P and stable P increased.（2）There was a significant negative correlation between active P and tobacco leaf quality,the active P showed significant negative on oil content,maturity,color and other appearance quality,aroma,irritant,flammability,gray and other sensory evaluation quality,and physical properties such as potassium,chlorine and stalk content.However,there was a significant positive correlation with aroma quantity,odor quality,reducing sugar,total sugar and other chemical substances.With the increase of soil available P content（43.67 mg/kg,78.66 mg/kg,167.00mg/kg）,the growth trend of flue-cured tobacco increased at the root extension stage,while the agronomic traits and root morphology of flue-cured tobacco increased first and then decreased at the flat-top stage.The dry matter accumulation,P accumulation,yield and output value of flue-cured tobacco increased as the improvement of available P level,and the most was obtained by 167.00 mg/kg treatments,and increased by 7.71-17.17%,20.33%-35.83%,0.95%-13.67%and 7.32%-27.60%,respectively.When soil available P was much more than 43.67 mg/kg,the tobacco leaf quality showed a decreasing trend,and the physical properties of flue-cured tobacco decreased firstly and then increased as the increase of soil available P.（3）Field experiments showed that the phosphorus application rate in the range of94.5-126 kg/hm²could not only satisfy the growth of flue-cured tobacco,but also get better yield and output value.In P enriched soil（available P 50.94 mg/kg）,application of P2O5 fertilizer could still promote the growth of flue-cured tobacco,and the effect was more obvious in the second year comparing to no phosphate fertilizer application.The results of two years showed that the best agronomic traits could be obtained by the phosphorus（P₂O₅）application rate of 94.5 kg/hm².The accumulation of N,P and K in flue-cured tobacco increased firstly and then decreased with the increase of P2O5application rate,and the maximum value was obtained by the P₂O₅application rate of157.5 kg/hm²in first year and 94.5 kg/hm²for second year,respectively.The results of two years’experiment showed that 94.5-126.0 kg/hm²phosphorus（P₂O₅）application could obtain higher output value and better appearance and sensory quality of tobacco leaves.With the increase of P₂O₅application rate,the content of available P and various forms of P in soil basically increased,and the proportion of active P in total P increased by 2.40-5.48 percentage points.In conclusion,the higher available P content of Enshi tobacco soil was found,and is the mainly P form was Na OH-P.With the increase of soil available P content,the content of all P forms increased,but the increase of active P reduced the sensory evaluation quality and appearance quality of flue-cured tobacco.Therefore,the recommended application amount of phosphorus fertilizer was 94.5 mg/kg-126 mg/kg for phosphorus enriched tobacco planting soil in Enshi.