| Flue-cured tobacco is one of economic crops which relys on both yield and quality. Although many factors affect the production and quality of tobacco, soil condition is the primary environmental factor affecting the quality of tobacco leaves under given conditions of climate, varieties and cultivation management. A suitable soil condition is the base for high quality and optimium production of tobacco, and thus the status of soil nutrient is the basis of nutrient regulation and fertilization for tobacco. Due to a lack of systematical evaluation for the soil fertility in this decade, the status of soil fertility is not clear and this results in unreliable fertilization basis in tobacco growing area in Chongqing, affecting the production and quality of tobacco. To understand the current status of soil nutrient, all of eleven tobacco-growing counties in Chongqing have been chosen to conduct a systematic investigation during2012and2013cropping seasons.2777soil samples were collected according to the principle that at least one soil sample was collected in each planting unit based on "modern tobacco agricultural planning". Thereafter, soil pH, organic matter and nutrient content were analyzed and the soil fertility status was clarified. Furthermore, changes of soil fertility were understood by comparing with data from10years ago. Finally, the integrated soil fertility was evaluated by the fuzzy comprehensive evaluation and the nutrient distribution diagrams were carried out by GIS technology to provide infromation for soil improvement and scientific fertilization in tobacco growing area in Chongqing. The results are shown as follows:1. The soil pH of tobacco growing area in Chongqing is low. It ranges from3.8to8.5, with the median of5.5and mean of5.7, respectively. The proportions of the strongly acidic soil (pH＜5.0), acidic soil (pH5.0-5.5), most suitable soil (pH5.5-6.5) and neutral and alkaline soil (pH＞7.0) are29.0%,20.6%,29.5%,18.6and11.3%, respectively. Compared with2002, mean of soil pH value decreases by0.33, indicating an obvious soil acidification in tobacco-growing area in Chongqing. The proportion of strong acidic soil increases from16.0%in2002to29.0%in2012. The decrease of soil pH is significantly correalated with decrease in content of exchangeable cations. Therefore, alkaline soil amendments or fertilizers should be recommended.2. The mean of soil organic matter content (SOM) in soils of tobacco growing area in Chongqing is25.7g/kg, with84.7%of soils ranging from15to35g/kg. At present,67.4%of soils with SOM ranged from20-35g/kg are suitable for growing tobacco. The average of soil organic matter is almost the same with10years ago, whereas soil nitrogen (N) status increases significantly. The means of soil total N and available N are1.69g/kg and124.0mg/kg, respectively. Compared with10years ago, the current soil total nitrogen and available nitrogen content increase by0.56g/kg and69.4mg/kg, respectively. Due to the fast buildup of soil nitrogen, the application of nitrogen fertilizer should be reasonably controlled during growing tobacco.3. Spatial variation of soil phosphorus (P) status in tobacco growing area is large. The mean of soil total phosphorus and available phosphorus is0.64g/kg and28.8mg/kg, respectively. Proportion of soils with suitable available phosphorus for growing tobacco (15-30mg/kg) is34.0%, while the percentage of soils with low or high P content soil is26.8%and39.3%, respectively. The mean of soil available P increases by13.6mg/kg, and the percentage of soils with low P content (＜10mg/kg) decreases by29.1%, while the percentage of soils with high P content increases by20%when compared with that in2002. In county level, P deficient soils (available phosphorus<15mg/kg) is prevalent in Youyang and Nanchuan, which accounts for50.8%and38.0%of tobacco growing area, respectively. Thus, regional P fertilization is recommended.4. The spatial variation of soil potassium (K) content is large, with coexistence of deficiency and excess. Soil total K ranges from0.97to31.95g/kg with a mean of16.8g/kg. There are43.2%of soils with low total K content (15-20g/kg). Among the counties, Youyang followed by Qianjiang has lowest soil total K content, indicating a poor potentiality of supplying capacity of soil K. The mean of soil available K is210.5mg/kg with32.7%of soils having low available K (＜150mg/kg). Compared with2002, the average content of current soil total K decreases by10.7g/kg and the percentage of soils with high K content (>20g/kg) reduces remarkablely; but the average of the soil available potassium increases by53.7mg/kg and the percentage of soils with available K less than150mg/kg reduces by21.6%. The available K content in tobacco growing soils is higher than that of other soils, but tobacco needs larger amount of potassium. Considering that soil supply capacity of K is low and one third of soils have low available K content for growing tobacco. Therefore, K fertilizer should be applied according to local/regional conditions.5. The status of soil exchangeable calcium (Ca) and magnesium (Mg) is low. The mean of soil Ca and Mg content in2012is5.49and1.56cmol/kg. According to classification that the suitable ranges for tobacco growing are from6to10cmol/kg for Ca and from1.0to1.6cmol/kg for Mg, the percentage of suitable soils is26.4%and27.4%, respectively. The percentages of soils with low Ca and Mg content are63.7%and40.3%, separately. The mean content of the soil Ca decreases by4.5cmol/kg and soil Mg increases by0.4cmol/kg comparing with that in2002. Because the content of soil exchangeable Ca is obviously declined than2002, the amendment and fertilization containing Ca and/or Mg should be applied. Conversely, soil sulfur content ranks high and application of fertilizer containing surfur should be controlled.6. The means of soil available iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), molybdenum (Mo) and chlorine (Cl) are58.75,52.73,2.58,1.84,0.23,0.15and9.37mg/kg, respectively. The percentages of soils with high Fe, Mn, Cu, Zn contents are92.9%,73.8%,79.4%and50.7%, respectively. According to soil nutrient classification, the content of soil available B and Mo rank low, and the percentage of B and Mo deficient soils account for85.0%and68.7%, respectively. Comparing the data in2002, the content of soil Fe and Mg increases significantly, and the content of soil Cu, Zn and Mo changes little, but soil B content reduces greatly. For fertilization management, on the one hand, toxicity of Fe and Mn on tobacco growth should avoid, and on the other hand, rational application of B and Mo fertilizer is recommended.7. The integrated fertility index (IFI) obtained from fuzzy comprehensive evaluation is significantly and positively correlated with the yield, the proportion of first-class tobacco, and the output value of flue-cured tobacco. Therefore, IFI is a useful parameter to evaluate soil fertility of tobacco growing area in Chongqing.8. According to the above results, we suggest that:(1) Alkaline amendments or fertilizers should be applied to amend strongly acidic soil.(2) N fertilizer should be strictly controlled and P, K fertilizers should be applied according to local/regional conditions.(3) Fertilizers containing Ca, Mg, Mo and B should be applied especially in strongly acidic soil. |
