Effects Of Long-term Cultivation And Fertilization On Tobacco-grown Soil Productivity And Nutrients

Tobacco(Nicotiana tabacum L.)is one of the most important cash crops in China.The yield and quality of tobacco leaves are affected by cropping patterns and fertilization.Due to the lack of land resources in China,the continuous cropping of tobacco is common.Meanwhile,tobacco is also a crop that needs more fertilizer.A long-term continuous cropping and high input fertilization have resulted in the decline of tobacco field productivity,continuous cropping obstacles,deterioration of soil physicochemical and biological properties,unbalanced accumulation of nutrients,reduction of fertilizer utilization rate,and environmental pollution.More amounts of fertilizer have been applied to maintain high tobacco production,which makes the above-mentioned situations worse.However,the research on tobacco cropping patterns and fertilization is mainly based on short-term experiments,which is difficult to comprehensively and systematically understand the variation trend of tobacco productivity and fertility under long-term cropping patterns and fertilization.As a result,the Zunyi Tobacco Company has established a long-term fertility and fertilizer efficiency monitoring base in Sancha Tobacco Science and Technology Park in 2004.The experimental treatments covered the main local cropping patterns(continuous cropping of tobacco and tobacco-maize rotation)and fertilization techniques(single application of chemical fertilizer and combined application of chemical fertilizer and manure).Based on the long-term monitoring data of fertilizer efficiency and soil fertility in tobacco fields between 2004 and 2020,this study investigated the changes in tobacco field productivity,soil nutrients and microbial population from the perspectives of crop yield,nutrient input(fertilization and rainfall),nutrient output(including leaching and crop uptake)and microbial population under continuous cropping of tobacco and tobacco-maize rotation,single fertilization of chemical fertilizer and combined fertilization of chemical fertilizer and manure.We revealed the influence of these local cropping patterns and fertilization technology on crop yield and soil,and the generated results could provide scientific basis and practical support for maintaining a long-term,healthy and sustainable tobacco production.The main results are as follows:(1)No significant differences in yield and quality of tobacco leaf in most years were observed between continuous cropping tobacco and tobacco-maize rotation.The disease was the main reason for the yield decrease of continuous cropping tobacco in some years.In winter,ryegrass was planted in the soil of continuous rotation tobacco field for reducing the continuous cropping obstacles of tobacco.No significant differences in the yield and quality of crops(referred to as tobacco,corn and ryegrass,the same below)between combined fertilization of chemical fertilizer and manure and single fertilization of chemical fertilizer at the beginning for a long period of time,and then the crop yield was higher under the former than the latter fertilization.The yield of crops was lowest under the no-fertilization control.These results showed that the long-time beneficial effect of combined fertilization of chemical fertilizer and manure on crop yield.(2)Crop nutrient uptakes were similar between tobacco-maize rotation and continuous cropping in most years.Crop nutrient uptake no-fertilization control was lowest,and no significant differences in the crop nutrients uptake at the initial stage between the combined fertilization of chemical fertilizer and manure and the single fertilization of chemical fertilizer,while the former had significantly higher nutrient uptake than the latter in recent years.In addition,the economic benefit of fertilizer(the economic yield per unit fertilizer)had kept stable for a period of time and its the decrease of the single fertilization of chemical fertilizer and the increase of combined fertilization of chemical fertilizer and manure showed a significant difference in recent years.(3)The leaching losses of soil nutrients were mainly as NO₃^--N and K,which were22.69-39.7 kg ha^-1 and 16.35-32.39 kg ha^-1,respectively,accounting for 19.1-40.54%and7.76-18.65%of the fertilized amounts.The P leached by underground runoff is negligible.The tested yellow soil is rich in iron and aluminum,with a strong fixation effect on P,while its adsorption effect of soil colloid on NO₃^--N and K is weak,which may be an important reason for the above phenomenon.The leaching loss of N and K in soil and manure was significantly lower under combined fertilization of chemical fertilizer than under single fertilization of chemical fertilizer,indicating that a long-term application of manure promoted the formation of macroaggregates could reduce the leaching loss of N and K.(4)Contribution of P and K input from rainfall to crop nutrition could be ignored.The amount of N input in rainfall was 20.89-23.2 kg ha^-1 year^-1,accounting for 16.02-16.85%of the total amount of fertilizer applied to tobacco.NH₄⁺-N,NO₃^--N and soluble organic nitrogen in rainfall accounted for 39.65-49.37%,24.74-32.29%and 24.12-30.33%of the total N deposition,respectively,indicating that the wet deposition of nitrogen could supplement the N nutrition of tobacco crops,especially under the no-fertilization control.(5)In the Fertilization,the contents of total N,P,K and available N,P,K increased with the extension of planting time,indicating that the nutrient input was greater than the nutrient output in the fertilized soil;However,there were no significant differences in soil nutrient content between rotation and continuous cropping,indicating an insignificant effect of cropping systems on soil nutrient deficit.The combined fertilization of chemical fertilizer and manure increased the proportion of soil macroaggregates(>0.25 mm),especially the amount of 0.053-0.25 mm aggregates in macroaggregates.The combined application of chemical fertilizer and manure increased the proportion of soil macroaggregates(>0.25 mm),especially the amount of 0.053-0.25 mm aggregates in macroaggregates.The contribution rates of the former(>0.25 mm aggregates)to soil N,P and K increased from 51.52%,52.31%and 62.56%(chemical fertilizer alone)to55.34%,57.27%and 63.92%(chemical fertilizer combined with manure);The contribution rate of the latter(0.053-0.25 mm aggregate)to soil N,P and K increased from 28.27%,28.85%and 30.33%(chemical fertilizer alone)to 30.36%,33.49%and31.54%(chemical fertilizer combined with manure).(6)Compared with continuous cropping of tobacco and single fertilization of chemical fertilizer,the soil microbial biomass C and N,the diversity of bacterial and fungal communities increased significantly in the soil under combined fertilization of chemical fertilizer and manure and tobacco-maize rotation,indicating that the application of manure and tobacco-maize rotation improved soil environment for the microbial survival,growth and reproduction of microorganisms,which benefited to soil organic matter and nutrient cycling.In addition,the relative abundances of soil microorganisms related to the synthesis of sucrase,amylase,cellulase,urease,nitrate reductase and nitrite reductase,as well as the organic acids and H⁺secreted by soil microorganisms were all increased,which benefited to the transformation of soil C and N and the dissolution of insoluble P.In conclusion,the model of"tobacco-maize rotation(winter ryegrass)+combined fertilization of chemical fertilizer and manure"has played the best overall performance in increasing crop yield,soil macroaggregates formation,soil microbial biomass and population diversity,and also insoluble P activation,while decreasing NO₃^--N and K leaching,which can be adopted in the tested tobacco plantation areas.