Productivity,Nitrogen And Potassium Of Tobacco-grown Soils Under Long-term Cultivation And Fertilization Conditions

Guizhou is the second-largest tobacco-grown province in China.Flue-cured tobacco（hereafter,it is abbreviated to tobacco）is the main economic source for local farmers and governments.Although continuous tobacco cultivation has numerous drawbacks,tobacco/corn rotation and successive tobacco cultivation in summer are still the two main land use modes that have existed in the local area for a long time.This is because of the intensive population,limited arable land resources,and high economic benefits to growing tobacco compared to other summer crops.However,few long-term investigations were now performed on fertilization in different tobacco cropping systems.Nitrogen（N）and potassium（K）chiefly supplied from fertilizers are important for tobacco yield and quality,which are also quite active in soils.To rationally fertilize,it is of great significance to study N and K states in soils fertilized differently in these two tobacco cropping systems.Based on the long-term field experiment established in2004 in Zunyi,Guizhou Province,we studied tobacco agronomic performances（yield,quality,nutrient absorption,utilization efficiency,etc.）and soil N,K,and biological activities in 2021-2022.The tobacco growing systems included continuous tobacco cropping and tobacco/corn rotation with different fertilization modes（i.e.chemical fertilizer alone and chemical fertilizers in combination with organic fertilizers）.The main objectives were to understand the effects of long-term cropping and fertilization on tobacco performances and N and K states in tobacco-grown yellow soil and to provide a theoretical basis for rational tobacco cultivation and fertilization in tobacco-growing areas in Zunyi.The main research results obtained are as follows:（1）Compared with continuous tobacco cultivation,long-term tobacco/corn rotation increased tobacco leaf yield by 19.1～46.9%and output value by 21.9～57.6%,respectively.N and K in tobacco leaves in the tobacco/corn rotation system were higher in contrast to Cl and nicotine which behaved otherwise.As a result,K/Cl and N/nicotine ratios were more coordinated.Compared with chemical fertilizers alone,long-term chemical fertilization in combination with organic fertilizers increased tobacco yield by10.7～33.7%and output value by 14.9～42.9%.Tobacco leaves also contained higher K and suitable sugar and protein,making the K/Cl ratio and Schmuk value more harmonious.Long-term fertilization with chemical and organic fertilizers also significantly improved corn and green manure yield.（2）In the tobacco/corn rotation system,corn showed higher phosphorus（P）absorption,fertilizer agronomic efficiency,fertilizer economic efficiency,and fertilizer partial productivity than tobacco in the continuous cropping system,while tobacco K uptake was much higher than corn.Compared with only chemical fertilizer treatment,long-term fertilization with chemical and organic fertilizers increased crop K uptake by42.1-45.3%,agronomic efficiency by 23.6-34.5%,and partial productivity by13.8-31.3%,respectively.Therefore,chemical fertilization in combination with organic fertilizers increased fertilizer economic benefits,promoted crop（tobacco and corn）nutrient uptake and utilization from the soil,and improved the productivity of soils for cropping tobacco.（3）Compared with only chemical fertilizers,the long-term fertilization with chemical and organic fertilizers remarkably increased soil Na OH-hydrolyzed N,NH₄⁺-N,NO₃^--N,and microbial N,indicating active N transformation in the soil,being conducive to crop nutrient uptake and utilization.Moreover,long-term organic fertilization greatly increased the activity of soil enzymes such as protease,urease,nitrate,and nitrite reductase,promoting N conversion in the soil and improving soil N supply.Person correlation analysis showed significant positive correlations between the contents of available N and the activities of these four enzymes in the soil(r=0.732^**～0.961^**,n=18,P≤0.01).Compared with long-term continuous tobacco cropping,tobacco/corn rotation tremendously increased NO₃^--N in the tobacco-grown soil,improving the N supply from the soil as well as the growth and development of tobacco plants in the rotation system.（4）Compared with continuous tobacco cropping,long-term tobacco/corn rotation significantly increased non-exchangeable K by 4.7-8.0%,exchangeable by K 4.4-5.8%,and water-soluble K by 7.1-22.8%in the soil.Compared with chemical fertilizer alone,the long-term fertilization with chemical and organic fertilizers also increased these three K forms with increased rates of 6.8-10.2%,9.7-11.1%,and 8.2-24.2%,respectively.（5）Soil N and K in different forms showed significant positive correlations with crop（tobacco and cron）yield,quality,nutrient absorption,and nutrient utilization efficiency.Of those,Na OH-hydrolyzed N,NH₄⁺-N,NO₃^--N,microbial N,non-exchangeable K,exchangeable K,and water-soluble K are all positively correlated with tobacco yield(r=0.752^**-0.965^**,n=18,P≤0.01).Available N in the soil was also positively correlated with N,nicotine,total sugar,and protein in tobacco leaves,with a correlation coefficient ranging from 0.656^**-0.831^**（n=18,P≤0.01）.In addition,non-exchangeable and exchangeable K in the soil had positive correlations with nicotine and K in tobacco leaves(r=0.911^**-0.960^**,n=18,P≤0.01)but negative with Cl in tobacco leaves r=-0.890^*,n=18,P≤0.05).In summary,long-term tobacco/corn rotation and fertilization with chemical and organic fertilizers significantly accelerated N and K transformation,improved N and K availability,stimulated soil enzyme activity,and increased microbial biomass in the soil,resulting in the improvement of tobacco yield and quality.In the tobacco-growing regions of northern Guizhou,therefore,tobacco/corn rotation and application of chemical fertilizers in combination with organic fertilizers are advantageous for the sustainable development of tobacco cultivation,being worthy of advocating.