KONG Wu-yuan ,PI Ben-yang ,CAO Ming-feng ,XU Jian-qiang ,SUN Jin-zhao ,PEI Long ,ZHU Li

1.Linli County Branch of Changde Tobacco Company,Linli 415200,PRC;2.Changde Tobacco Company,Changde 415000,PRC;3.Shimen County Branch of Changde Tobacco Company,Shimen 415300,PRC

Abstract In order to find out the main nutrient content of tobacco planting soil and the changing characteristics of tobacco quality in Linli County,the sampling survey data of tobacco planting soil samples in Linli in 2000 and 2015,and the main chemical components,appearances and sensory qualities and physical indexes of B2F and C3F tobacco leaves from 2000 to 2015 were comprehensively analyzed and evaluated.The results showed that:the available phosphorus increased by 6.10%per year and the pH value of tobacco planting soil increased in a small range year by year,the organic matter content decreased year by year,the alkali hydrolyzable nitrogen showed a downward trend,and the water-soluble chlorine showed a rapid downward trend;the soil fertility index (SFI) was at the "high" level;in 2000—2015,the quality of tobacco leaf was relatively stable and the quality was good.In Linli tobacco planting area,the application of nitrogen control,phosphorus reduction and chlorine supplement and increase of organic matter could help us achieve the goal of high quality and efficiency of tobacco production.

Key words Tobacco planting soil;Nutrient content;Tobacco quality

1.Introduction

Soil is an important material basis of crop production,and it is also one of the important factors affecting crop yield and quality[1-2].Soil nutrients are a major source of nutrients for crop production and the change of soil nutrient content will affect the nutrient management measures of crop production[1,3].While the change of tobacco planting soil nutrient content would affect the growth,yield and quality of tobacco as well as fertilization measures[4-6].A great deal of research has been carried out in China on the effects of soil nutrient changes and soil fertility on the yield and quality of tobacco as well as water and fertilizer management,and some research results have been achieved.

Linli County which has the characteristics of sufficient sunshine,abundant rain and concentration in late spring and early summer,drought in summer and autumn,and about 270 d of frost free period,is an important tobacco with high quality production area in northwestern Hunan,located at 111°24'～111°49'E and 29°17'～29°46'N.In this study,the changing characteristics of soil nutrients and quality of tobacco planting in Linli County over the years were evaluated scientifically,so as to provide theoretical basis for tobacco planting soil nutrient management and scientific fertilization in Linli County.

2.Materials and Methods

2.1.Data sources

The data were obtained from the sampling survey data of 96 tobacco planting soil samples in Linli in 2000 and 2015.Soil nutrients were classified according to the Provisional Technical Regulations for the Second National Soil Survey[9].The classification standards of tobacco planting soil nutrients in Hunan Province were shown in Table 1.The soil pH value,alkali-hydrolyzable nitrogen,available phosphorus,available potassium,organic matter,chloride ion,total nitrogen,total phosphorus,total potassium and other related data were classified and statistically processed.Data of appearance quality,evaluation quality,content of main chemical components and physical indexes of B2F and C3F tobacco leaves came from the determination results of samples sent for inspection in Linli County from 2000 to 2015.

2.2.Calculation of soil fertility index (SFI)

The comprehensive soil fertility index (SFI)is a comprehensive index reflecting the soil fertility status of tobacco planting.The higher the value is,the higher the comprehensive soil fertility level is.The comprehensive evaluation of tobacco planting soil fertility was carried out by using the fuzzy comprehensive evaluation method.First,the comprehensive soil fertility index (SFI) of tobacco planting in each place was calculated,and then the comprehensive evaluation grading standard (Table 2) was made according to the SFI value to divide the soil,and the soil proportion of each fertility level was obtained.The comprehensive soil fertility index was evaluated by using mathematical model of fuzzy mathematical membership function.

2.3.Statistic analysis of data

Excel and DPS v7.05 software were used for datastatistics.The appearance quality,physical property and sensory evaluation quality of tobacco were evaluated by selecting corresponding indexes referring to the China tobacco planting regionalization and using weighting method[11].The comprehensive total score was calculated as the evaluation basis of tobacco quality.SPSS 14.0 was used to analyze tobacco data.

Table 2 Classification standard for SFI of tobacco planting soil nutrient in Hunan Province

3.Results and Analysis

3.1.Variation of main nutrients contents in soil

As shown in Table 3,pH value of tobacco planting soil in Linli increased by 2.02% from 2000 to 2015,showing a trend of slow increase.The soil with appropriate pH value (5.5～7.0) accounted for 58.90%;while the soil with a pH value below 5.5 accounted for 40.00%.It was feasible to reduce the proportion of tobacco planting soil with pH value below 5.5 through fertilization and soil improvement measures.The organic matter contents in soil decreased by 6.33%,with an average annual rate of 0.40%.The soil with appropriate organic matter contents (25～35 g/kg) accounted for 54.40%,with low organic matter contents (10～15 g/kg) accounted for 38.90%.Therefore,it was urgent to increase the organic matter contents of tobacco planting soil.The alkali-hydrolyzable nitrogen contents of soil decreased by 3.75%,but the alkali-hydrolyzed nitrogen contents in 96.70% of soil was higher than the optimum value,thereby,it was sufficient to meet tobacco production requirements.However,the total nitrogen of soil decreased by 7.69%,while alkali-hydrolyzed nitrogen mainly came from the input of chemical nitrogen,therefore,increasing the total nitrogen content in soil was an urgent issue to be solved in current production.The available phosphorus contents in soil increased by 91.47%,with an average annual rate of 5.72%.The available phosphorus contents in 88.90% of soil was higher than the optimum value.Moreover,the total phosphorus contents of soil increased by 13.21%.Therefore,the available phosphorus of soil was sufficient to meet the requirements of tobacco production,and the application amount of chemical phosphorus fertilizer can be appropriately reduced in production to improve its utilization rate and reduce the input cost of phosphorus fertilizer.The available potassium contents increased by 64.06%.The proportion of soil exceeding the appropriate value was 43.30%,with an average annual increase of 2.71%.The soil with low level available potassium reached up to 56.70%,indicating that more than half of the soil in Linli County still cannot meet the requirements of current production.Therefore,increasing the effective supply of available potassium was the key fertilization technique to improve the yield and quality of tobacco.The contents of water-soluble chloride ions in the soil decreased by 68.22%,with an average annual decrease of 0.46 mg/kg.The soil with appropriate level water-soluble chloride ions contents accounted for 7.78%,with low and extremely low level watersoluble chlorine accounted for 92.22%.Therefore,chloride fertilizers should be applied appropriately in production to improve the imbalance of mineralelements caused by soil chlorine deficiency.

Table 3 Variation of main nutrients contents of tobacco planting soil in 2000—2015

3.2.Variation of comprehensive soil fertility index (SFI)

As shown in Table 4,the average of SFI in Linli County reached up to 0.72.The proportion of soil with extremy low level SFI was 0.The soil with low level SFI accounted for 3.33%.The SFI of 96.67%soil was higher than the appropriate level (including appropriate level).This indicated that the SFI in Linli County was at a high level.

3.3.Variation of main quality index in tobacco

As shown in Table 5,the average comprehensive scores of appearance quality,evaluation quality,main chemical components and physical properties of the C3F and B2F tobacco samples sent for inspection in Linli County from 2000 to 2015 were 80.30 and 77.20 respectively.The comprehensive scores of 95.03% B2F tobacco was higher than 70.00,4.97%B2F tobacco was at 60.00～70.00.The comprehensive scores of 97.49% C3F tobacco was higher than 70.00,2.51% C3F tobacco at 60.00～70.00.This indicated that the comprehensive evaluation value of tobacco leaves in Linli County was at a high level,the quality of tobacco leaves was stable and the quality was good.

Table 4 The comprehensive soil fertility index (SFI) of Linli in 2000—2015

Table 5 Comprehensive quality evaluation of B2F and C3F tobacco leaves in 2000—2015

4.Discussion and Conclusion

The yield and quality of tobacco leaf are closely related to the comprehensive soil fertility index(SFI),and the pH value of the soil,as well as the contents of the main nutrients such as organic matter,alkali-hydrolyzed nitrogen,available phosphorus and available potassium are important indexes to evaluate the SFI[8-9].Soil pH value mainly depends on the concentration of hydrogen ions in the soil solution,which is closely related to the concentration of mineral ions in the soil,the availability of soil nutrients and the growth of crops.Organic matter is an important component of soil solid phase which has an important influence on soil formation and soil fertility.Soil alkali-hydrolyzale nitrogen provides the available nitrogen for direct uptake by plants,and its content is closely related to the content and quality of organic matter,which is the index of soil nitrogen availability.Available phosphorus includes all watersoluble phosphorus,some adsorbed phosphorus,some slightly soluble inorganic phosphorus and organophosphorus that are easy to mineralize,etc.Improving the availability of soil phosphorus mainly depends on adjusting soil pH value and increasing soil organic matter.The content of available potassium is one of the important indexes reflecting soil potassium supply,which includes potassium in soil solution and exchangeable potassium in soil,accounting for 0.1%～ 2% of the total potassium in soil.Chlorine ion is one of the essential mineral elements in tobacco production,and too low or too high chloride ion content in soil will not be conducive to tobacco production[10,12].As shown in Table 3,the SFI in Linli County was at a high level,whereas the contents of potassium and chlorine could not meet the requirement of tobacco production.

In addition to environment factors such as soil texture,the deficiency of mineral nutrients in soil are also closely related to fertilization management technology,which can make up the deficiency of mineral elements in soil to a certain extent.Based on the current situation of a high level of SFI but a low level of potassium and chlorine contents in Linli planting tobacco soil,the fertilization measures of“nitrogen control,phosphorus reduction,chlorine supplement,the increase of organic matter and the change of phosphorus fertilizer type”should be taken to improve organic matter contents in soil,decrease pH value,balance the contents of mineral elements in soil and provide material base high-quality tobacco leaf production.