Chunwen YANG,Yu ZHAO,Xinzhong WANG,Chengwei YANG,Zhijuan YANG,Yanxia HU,Junwei SUN,Dexun WANG

1.Dali Branch of Dali State Tobacco Company,Dali 671000,China;

2.Yunnan Agricultural University,Kunming 650201,China;

3.Dali Branch of Yunnan Provincial Tobacco Corporation,Dali 671000,China

Responsible editor:Nanling WANG Responsible proofreader:Xiaoyan WU

Soil is a basis of tobacco cultivation,soil nutrient status of tobacco-growing areas directly affects the growth and the quality of flue-cured tobacco[1],and soil pH value is one of the decisive factors affecting the effectiveness of soil nutrients,too high or too low pH values of soil will change the effectiveness of soil nutrients[2-3],causing the imbalance of some elements of plants,thus affecting the yield and the quality of fluecured tobacco[4-5].Therefore,the relationship between soil pH and nutrients has attracted the attention from schol ars at home and abroad[6-9].Dali Prefecture is Dali main tobacco areas,but there is still a lack of in-depth study on soil nutrients.In this paper,on the basis of the whole city soil samples in 2012,the distribution characteristics of soil pH values and its correlation with soil nutrients in tobacco-growing areas were analyzed to provide a theoretical basis for guiding flue-cured tobacco field cultivation in Dali City.

Materials and Methods

Overview of research areas

Dali City is in the middle of Dali Bai Autonomous Prefecture,and located at 99° 58′ -100° 27′ E and 22°25′-25°58′ N,belongs to subtropical monsoon climate with low latitude and plateau,moreover,it has small seasonal temperature difference and large diurnal temperature difference,its annual mean temperature is 15.1 ℃,annual mean precipitation is 1 055.0 mm,and annual mean sunshine hours are 2 228 h.

Sample collection

After picking and baking in 2012,43 samples from 8 tobacco-growing towns in Dali City were collected.The specific sampling methods were as follows:One soil sample should be selected from each 40 hm2,diagonal lines must be drawn on a sampling unit or continuous areas,10 points which distributed evenly in each diagonal line should be chosen; then soil samples with 0 -20 cm topsoil from the 20 points were collected and mixed,after that,1 kg soil samples were taken as one soil sample using quartering method; and then after air drying,grinding,sieving,blending and bottling,the determination and analysis was carried out.

Determination methods of indexes

The determination methods of main indexes were as follows:Using pH meter method to determine soil pH value[m(water):m(soil)=2.5:1.0]; using oxidized method with potassium dichromate to determine soil organic matter; adopting alkaline hydrolysis diffusion method to determine alkalihydrolyzale nitrogen; adopting sodium bicarbonate digestion and Mo-Sb colorimetric method to determine available phosphorus;adopting ammonium acetate digestion flame photometry to determine available potassium; and adopting ammonium acetate digestion and atomic absorption spectrometry to determine exchangeable calcium and exchangeable magnesium.The specific determination methods of each index were as reference[10].

Results and Analyses

Basic situation of soil pH values

As shown in Table1,pH values of tobacco-growing soil in Dali City were generally suitable,and the average value was 6.52 ±0.62,the change range was among 5.44 -7.72,the variation was less and the variable coefficient was 9.51%.Hereinto,the soil with the most suitable pH for the growth of flue-cured tobacco (namely,pH values were among 5.5-6.5) accounted for 44.18%,and the soil with the suitable pH for the growth of fluecured tobacco (namely,pH values were among 5.0-7.0) accounted for 72.09%,as well as the soil with unsuitable pH for the growth of flue-cured tobacco (namely pH ＞7.0) accounted for 27.91%.

The distribution of pH values of different soil types

Soil types of tobacco-growing areas in Dali City were red soil,paddy soil,alluvial soil and purple soil,in which red soil and paddy soil occupied a larger proportion,namely 27.9%and 67.44%,respectively.As seen in Table2,the pH values of different soil types in a descending order were as follows:alluvial soil(7.09)＞paddy soil (6.55)＞purple soil (6.44) ＞ red soil (6.38).Hereinto,the percentages of soil samples with the suitable pH for the growth of flue-cured tobacco (namely,pH values were among 5.0-7.0)in total samples from high to low were:alluvial soil,purple soil (100%)＞red soil(75.0%)＞paddy soil(68.97%).

The distribution of soil pH values of different altitudes

Tobacco-growing soil in Dali City was distributed at the altitude of 1 780-2 200 m,in which the soil with the altitude below 2 100 m occupied 90.7%.From Table3,we inferred that with the increase of altitude,soil pH values showed a gradual decreasing trend;at the altitude of 1 780-1 990 m,average pH value of soil was 6.76; at the altitude of 2 100-2 200 m,average pH value of soil dropped to 6.16.In addition,at the altitude of 1 780-1 990 m,the percentage of soil samples with the suitable pH for the growth of flue-cured tobacco in total samples was 61.11%;at the altitude of 1 990-2 100 m,the percentage of soil samples with the suitable pH for the growth of flue-cured tobacco in total samples was 71.43%;and at the altitude of 2 100-2 200 m,all soil pH values were suitable for growth of flue-cured tobacco.

Contents of main nutrients in soil

Different soil nutrients had different changes,in which its variation degree of exchangeable magnesium was the greatest and its variable coefficient was 66.74%,however,the minimum change was alkali-hydrolyzable nitrogen and the variable coefficient was 38.16%.To facilitate the evaluation on soil fertility indexes of tobacco-growing areas,combined with the field experiment results of flue-cured tobacco cultivation in recent years and relevant references[11],soil nutrients of tobacco-growing areas were divided into the following five grades:very low,low,medium,high and very high.

Based on grading standard,or-ganic contents of tobacco-growing soil in Dali City were generally abundant and the average value was 30.30 g/kg,in which soil samples with medium level(15-25 g/kg) of organic content occupied 4.65%,moreover,organic content in all soil was at medium level or above; average content of soil alkalihydrolyzable nitrogen reached 211.42 mg/kg,in which 11.63% of soil samples was at medium level (100-150 mg/kg),and nitrogen deficiency soil(＜100 mg/kg) accounted for 6.98%; average content of soil available phosphorus was 35.34 mg/kg,in which 58.14% of soil samples was at medium level (20-40 mg/kg),and phosphorus deficiency soil (＜20 mg/kg)accounted for 11.63%; average content of soil available potassium was 144.25 mg/kg,in which 23.26% of soil samples was at medium level (150-220 mg/kg),and the proportion of potassium deficiency soil (＜150 mg/kg)reached up to 58.14%; average content of exchangeable calcium was 3.23 g/kg,in which 4.65% of soil samples was at medium level (0.8-1.2 g/kg),and calcium deficiency soil (＜0.8 g/kg)accounted for 2.33%; average content of exchangeable magnesium was 525.98 mg/kg,in which 4.65% of soil samples was at medium level (100-200 mg/kg),and magnesium deficiency soil (＜100 mg/kg) accounted for 4.65%.

Table1 Basic situation of soil pH values

Table2 The distribution of pH values of different soil types

Table3 The distribution of soil pH values of different altitudes

Table4 The description statistics of soil main nutrients

Table5 The relationship between soil pH values and soil nutrients

The relationship between soil pH values and soil nutrient contents

Seen from Table5,pH values of tobacco-growing soil in Dali City had significant positive correlation with exchangeable calcium and exchangeable magnesium contents in soil,and the correlation coefficients were 0.786 8 and 0.620,respectively; however,they had no significant correlation with other soil nutrient contents.

Conclusions

(1)It was generally acknowledged that the suitable soil pH for the growth of flue-cured tobacco was among 5.0-7.0,the most suitable soil pH for the growth of flue-cured tobacco was among 5.5-6.5.Average pH of tobacco-planting soil in Dali City was 6.52,thus it was generally suitable for sound tobacco cultivation.Soil samples which suited for flue-cured tobacco cultivation accounted for 72.09%of total samples.

(2) In four soil types of tobaccogrowing areas,the pH values in a descending order were as follows:alluvial soil＞paddy soil ＞purple soil ＞red soil,in which both red soil and paddy soil were suitable tobacco-growing soil;and the pH values of 25%red soil and 27.59% paddy soil were higher than 7.0,these soil pH values should be reduced by applying organic fertilizer,straw turnover,overrotten farmyard manure and physiological acidic fertilizer,etc.; the pH value of 3.44%paddy soil was still lower than 5.5,so its pH value should be adjusted to the suitable range by reducing acidic fertilizer or using alkaline fertilizer,and appropriately applying quick lime.

(3)At the altitude range of 1 780-2 200 m,soil pH values showed a gradual decreasing trend.At the altitude of 2 100-2 200 m,all soil pH values were suitable for growth of fluecured tobacco;followed by the altitude of 1 990-2 100 m,the percentage of soil samples with the suitable pH for the growth of flue-cured tobacco in total samples was 71.43%; at the altitude of 1 780-1 990 m,the percentage of soil samples with the suitable pH for the growth of flue-cured tobacco in total samples was 61.11%.

(4) The average contents of soil organic matters were relatively abundant and generally suited for highquality tobacco cultivation;the average contents of soil alkali-hydrolyzable nitrogen,available phosphorus,exchangeable calcium and exchangeable magnesium were generally at medium and abundant level,however,their rations under medium level in some tobacco-growing areas were 6.98%,11.63%,2.33% and 4.65%,respectively; moreover,average content of available potassium in soil was generally at a lower level,the contents at medium level or above only accounted for 41.86%,and available potassium content in 58.14% soil was lower (＜150 mg/kg); all these should be adjusted in formula fertilization strategies,especially the supplement of potassic fertilizer,to meet the need of high-quality tobacco cultivation.

(5) pH values of tobacco-growing soil in Dali City had significant positive correlation with exchangeable calcium and exchangeable magnesium contents in soil,however,they had no significant correlation with other soil nutrient contents.

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