Zhong SHEN, Xianghong LIU, Yigui LUO, Jiatian HU, Xu CHEN, Yanzhong LIU, Yu SI,Zhuanyong ZHANG

1. Hongta Tobacco (Group) Co. Ltd. of Zhaotong Cigarette Factory, Zhaotong 657000, China;

2. Yunnan Agricultural University, Kunming 650201, China;

3. Tobacco Companies in Yunnan Province Zhaotong City Company, Zhaotong 657000, China

High-quality tobacco production has been closely linked to soil environment, for soil nutrients and nutrient supplying capability are under influence of natural environment, ploughing, irrigation, and fertilization. With consideration of complex terrain and soils, it is necessary to perform a general investigation on soil nutrients in tobacco fields in Zhaotong City, which is of great significance for learning interannual changes of tobacco soils, optimizing cultivation measures and soil environment,as well as improving sustainable productivity of lands in Zhaotong City.

Materials and Methods

Soil sampling

On basis of tobacco fields in Zhaotong City, soils were sampled a total of 511, from Zhaoyang District,Qiaojia County, Yiliang County,Zhenxiong County, Yongshan County,Daguan County, Weixin County, and Ludian County in Zhaotong City during 2011-2013.

Analysis on soil samples

The value of pH was measured by potentiometry with water-to-soil ratio of 2.5 ∶1; organic matter was measured by potassium dichromate volumetric method; hydrolyzable nitrogen was measured by alkaline hydrolysis diffusion method; available P was by digestion with 0.5 mol/L NaHCO3and molybdate blue spectrophotometric method; rapid available P was measured by digestion with 1 mol/L NH3AC and an atomic absorption spectrophotometer; total N was by semimicrokjeldahl method (GB7177-87); total P was by NaOH fusion-Mo-Sb antispetrophotography method; total K was by NaOH fusion-flame photometry; chloridion was by extraction with boiling water and titrimetry with AgNO3.

Data analysis

The test data were analyzed with SPSS and Excel.

Grading standards of nutrients

The nutrients were graded as per the method[1-2].

Results and Analysis

Dynamic changes of pH values in tobacco soils in Zhaotong City during 2011-2013

The optimal values of pH were inthe range of 5.5-7.0 for tobacco. As shown in Table 1, pH value kept increasing during 2011-2013.With 7.0≤pH ＜8.5, pH value proved the highest in 2012, and the lowest in 2011.What’s more, the significance test proved significance difference of 0.029,lower than 0.05.It is known that pH value is much important for tobacco growth, and pH of tobacco soils in Zhaotong in 2013 is suitable for tobacco. However, attention should be paid to soil alkalization and fertilization measures should be well adjusted.

Changes of organic matter in tobacco soils in Zhaotong during 2011-2013

It is believed that organic matter content in the range of 20-30 mg/kg is suitable for tobacco growth in tobacco soils. As shown in Table 2, average organic matter was the least in 2011 and significance level kept higher than 0.05, suggesting that the differences were not so significant. Subsequently,significance testing was performed on averages from 2011 to 2013 and the results showed sig=0.065, which indicated that differences were not significant.It can be concluded that interannual content of organic matter kept stable of tobacco soils in Zhaotong. It is widely known that content of organic matter is a key index measuring nitrogen supplying capacity. Nevertheless,excessive organic matter affects ripeness and inner chemical quality of tobaccos. In Zhaotong, organic matter of tobacco soils maintained generally higher. Therefore, it is necessary to supplement organic matter in the areas with lower content and control fertilization amount in the areas with higher content in case of later-ripeness and affected quality.

Table 1 Changes of pH of tobacco soils in 2011-2013

Table 2 Changes of organic matter in tobacco soils in Zhaotong during 2011-2013

Table 3 Changes of total N in tobacco soils in Zhaotong during 2011-2013

Changes of total N in tobacco soils in Zhaotong during 2011-2013

Total N of soil is an important index evaluating nitrogen content of soil and the range of 0.10%-0.15%proves optimal.As shown in Table 3,nitrogen contents of tobacco soils below 0.05%or higher than 0.20% maintained decreasing, but increasing within the range of 0.15%-0.20%. According to significance testing,significance levels all kept higher than 0.05 in different ranges of total nitrogen, which indicated that the differences were not significant. During 2011 -2013, significance testing was performed on averages of each year, and the results showed that significance level was 0.247 higher than 0.05. Therefore, it can be concluded that nitrogen content in tobacco soils in Zhaotong maintained stable and higher in 2011 -2013.

Changes of hydrolyzable nitrogen content in tobacco soils in Zhaotong during 2011-2013

The content of hydrolyzable nitrogen represents nitrogen which can be directly used.It is known that the content of hydrolyzable nitrogen proves optimal in the range of 100-180 mg/kg for tobacco. As shown in Table 4, significance level of soil hydrolyzable nitrogen kept higher than 0.05, suggesting insignificant differences. During 2011-2013, the averaged hydrolyzable nitrogen content was located in the optimal range, with sig of 0.000,suggesting significant differences.Therefore, it is necessary to apply N fertilizer in a rational way. For example, more N fertilizers should be applied in the area with little nitrogen,but N fertilizers should be controlled in the area with higher content.

Changes of total P content in tobacco soils in Zhaotong during 2011-2013

Phosphorus is an essential element for tobacco growth and an optimal content promotes root growth,yellowing, and coordination of chemical components, with high industrial usability[3]. In practice, the range of 0.10% - 0.15% is ideal for tobacco growth. As shown in Table 4, significance levels of total P in tobacco soils were all higher than 0.05, suggesting that the differences were not significant. During 2011-2013, significance testing was performed on the averages each year, and the results showed sig=0.084, higher than 0.05,indicating insignificant differences. It can be concluded therefore that total P content maintained stable in tobacco soils sin Zhaotong. Besides, average total P contents all located in optimal ranges in the three years.

Changes of available P in tobacco soils in Zhaotong during 2011-2013

It can be concluded from Table 6 that available P content was below 10 mg/kg in tobacco soils in Zhaotong.Specifically, the content reached the highest in 2012 and the lowest in 2013.Besides,the significance testing showed sig=0.006＜0.05,indicating the differences were significant. On the other hand, the content of available P located in the range of 15-30 mg/kg and the averages was the highest in 2011 and the lowest in 2013. The significance testing showed sig=0.023 ＜0.05, indicating significant differences.In general, contents of available P were all in the optimal range from 2011 to 2013,but significance testing on averages showed sig=0.000, suggesting significant differences.

Changes of total K in tobacco soils in Zhaotong during 2011-2013

Potassium is an element representing K supplying capacity of soils and the optimal range is in 0.10%-0.15%. As shown in Table 7, significance levels of total K kept below 0.05 in different ranges, suggesting insignificant differences, and the significance testing on averages in different years indicated significant differences and interannual growing with sig =0.002.

Changes of available K in tobacco soils in Zhaotong during 2011-2013

Potassium is key for tobacco quality and the content of high-quality tobaccos generally maintains in the range of 150-220 mg/kg. As shown in Table 8,according to significance testing, significance levels were all higher than 0.05, suggesting insignificant differences, and the significance testing on averages suggested insignificant differences with sig=0.410.

Table 4 Changes of hydrolyzable nitrogen content in tobacco soils in Zhaotong during 2011-2013

Table 5 Changes of total P content in tobacco soils in Zhaotong during 2011-2013

Table 6 Changes of available P in tobacco soils in Zhaotong during 2011-2013

Table 7 Changes of total K in tobacco soils in Zhaotong during 2011-2013

Changes of Cl- in tobacco soils in Zhaotong during 2011-2013

Table 8 Changes of available K in tobacco soils in Zhaotong during 2011-2013

Table 9 Dynamic changes of Cl-content during 2011-2013 in Zhaotong

The content of Cl-tends to be volatile in soils in the range of 10-30 mg/kg.As shown in Table 9,within the range of 5-10 mg/kg, the averaged content reached the peak in 2011 and the lowest in 2012, and the significance level was 0.33,indicating significant differences. In the range of 10-30 mg/kg, average reached the highest in 2013 and changed insignificantly in 2011 and 2012, with significance level of 0.000. On the other hand, significance testing was performed on averages and the results showed sig=0.000, indicating significant differences.The content of Cl-was increasing from 2011 to 2013, but the content showed considerable differences in 2013 compared with those in 2011 and 2012.

Conclusion and Discussion

Soil pH is a key element for highquality tobacco cultivation[4]. For example, overhigh pH value would lead to lower contents of nicotine and K content and excessive low pH value would lead to overhigh nicotine content and lower sugar-to-alkali ratio. In Zhaotong, soil pH tends to be volatile in the range from 7.0 to 8.5, and kept increasing during the three years. Besides, significance testing was performed on averages in the years and the results showed sig =1.770, suggesting insignificant differences. In tobacco fields in Zhaotong, most tobacco soils are dominated by alkali soil,supplemented by acidified soils and it is necessary to make improvements on potential of hydrogen specifically to improve fertilizer use rate in tobacco production.

Organic matter content is an important index measuring nitrogen-supplying capacity of soils and either overhigh or excessive low content affects cured tobacco growth and quality.For example, if content of soil organic matter is lower,nitrogen-supplying capacity of soil would be weak,and nitrogen mineralization would occur,which is adverse for nitrogen absorbing and use by tobaccos. If organic matter content is overhigh, nitrogensupplying capacity would be stronger,resulting in nitrogen excess in later growth stage, so that ripeness would be later, and tobacco quality poorer[5].The significance testing was performed on averages from 2011 to 2013 and the results showed sig =0.065,which indicated that differences were not significant. Besides, averaged content of organic matter was growing during 2011-2013.In conclusion, organic matter content maintained higher in tobacco soils in Zhaotong and organic fertilizers should be reduced.

N, P and K are crucial elements affecting tobacco quality, of which P is a key factor influencing tobacco growth[6].According to significance testing, significance levels of total N and total P were both higher than 0.05 during 2011-2013, showing insignificant differences. The significance level of total K was 0.02, showing significant differences. Besides, significance levels of hydrolyzable nitrogen and available P were both 0.000, showing significant differences, and significance level of available K was 0.410, showing insignificant differences. On basis of averages in the years, averaged contents of N, P and K showed changed little. On the other hand, averaged content of total N is higher than the range suitable for high-quality tobacco growth in tobacco soils in Zhaotong,but contents of total P and total K are just within the range, which demonstrated that most tobacco soils would supply abundant N, P and K for tobaccos. Additionally, hydrolyzable nitrogen, available P and available K contents are also in the range.

Cl-is a necessary element for tobacco growth. However, overhigh content would affect tobacco combustibility, resilience and quality, and decrease industrial availability[7]. Excessive lower content would result in short plant, small leaf area, dim leaf color and poor leaf resilience.It can be concluded from Cl-content in tobacco soils that the averaged content was growing from 2011 to 2013 and the increase reached the highest from 2012 to 2013. According to significance testing, significance level was 0.000,showing significant differences. These incorporated that the content of Cl-changed dramatically of tobacco soils during 2011-2013. In practice, fertilization should be conducted according to Cl-content in soils. For instance, K fertilizer and chlorine fertilizer shouldbe applied in tobacco fields with lower Cl-content, and chlorine fertilizer should be controlled in tobacco fields with high Cl-content. It is notable that Cl is an unstable element and eluviation would cause Cl-loss[8]. Therefore,Cl-abundance or deficiency should be aware of timely at applying chlorine fertilizer in order to guarantee Cl-content of high-quality tobaccos for production.

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