| Flue-cured tobacco is an important commercial crop in China, and Sichuan Province is a main province that planting flue-cured tobacco. And Liangpan, northen Sichuan and southern Sichuan ecological zone are the main production areas of flue-cured tobacco. A good soil ecological environment is the basis of obtaining high-quality flue-cured tobacco, the supply of soil nutrient and the balance characteristics of nutrient is an important indicator to evaluate whether the soil ecological environment is balanced In this paper,955 flue-cured tobacco planting soil samples from three ecological zones of Sichuan was taken as the researched object, the contents of soil OC, TN, TP, TK, AN, AP and AK and its stoichiometry characteristics were measured and analyzed to discuss the supply and balance characteristics of flue-cured tobacco planting soil, in order to provide scientific basis for the regulation of soil quality and the sustainable development of flue-cured tobacco production in the study area. The main results are as follows:(1) The C, N, P and K content and stoichiometry characteristics of flue-cured tobacco-planting soil in Sichuan Province①The average contents of OC, TN, TP, TK, AN, AP, and AK in soil were 13.66, 1.50,0.72,18.30,131.18,12.35 and 102.48 g-kg-1, respectively. According to the standard of national soil survey, TN and AN was relatively rich for belonging to the second level, on the contrary, and the supply of TK, AP and AKwas medium for belonging to the third level, and TP was relatively lacking for belonging to the forth level, this is related to the focus on the influence and balance of N, K but ignore the influence and balance of P. Compared with the 2nd national soil survey, SOC has declined by 12.10%, while the TN, TP, TK and AN were enriched, increased by 7.9%, 20% and 1%, respectively. The content of AN increased by 12.33%, while the AP and AK decreased by 17.99% and 9.6%. It suggested that the soil nutrient was seriously unbalanced, the supplement SOC should be taken seriously.②The average value of C:N ratio of tobacco-planting soil in Sichuan Province was 10.80 which was within the national average value (10:1～12:1), it verifies that the value of C:N ratio was still in the appropriate range. Compared with the 2nd national soil survey, C:N, C:P and C:K ratios decreased by 12.22%,33.24% and 21.39%, respectively. It was related to the excessive consumption of SOC and the enrichment of total nutrients. N:P ratio decreased by 17.20% which was related to the different enrichment degree of N and P. P:K ratio raised slightly, this is because planting flue-cured tobacco caused the release of a part of K, and the other part of K was fixed by soil, and P was difficult to be absorbed by the plant and easy to be fixed by soil.③The significantly positive correlation between SOC and the N:P、N:K、P:K ratios which suggested that SOC was the main factors that influence the soil stoichiometry.(2) The C, N, P and K content and stoichiometry characteristics of flue-cured tobacco-planting soil in three main ecological zones of Sichuan Province①As a whole, the soil AN content in Liangpan ecological zone was rich which belongs to the second level, while TP was relatively lacking for belonging to the forth level. The soil AN in northen Sichuan ecological zone was very rich which at first level, while lacks in AP and AK. The tobacco-planting soil in southern Sichuan ecological zone was rich in TN and TK, while lacks in TP and AK. Each ecological zone appeared that some elements were enrichment but lacked in the other elements, and soil nutrients were seriously imbalanced and strongly limited by P and K. Compared with the 2nd national soil survey, dynamic changes of nutrient elements content in three main ecological zones were basically the same, the contents of SOC, AP and AK showed a decreasing tendency. The largest reduction of SOC and AP occurred in Liangpan ecological zone, decreased by 15.96% andl9.52%, respectively. The time of flue-cured tobacco planting in Liangpan ecological zone was the longest, which caused the excessive consumption of SOC. The largest reduction of AK occurred in southern Sichuan ecological zone, decreased by 12.50%. Howerer, the content of total nutrients were enriched, the largest amplification of TN and AN occurred in Liangpan ecological zone, increased by 14.52% and 14.24%, respectively. And the largest amplification of TP and TK occurred in northern Sichuan ecological zone, were 22.22% and 3.2%, respectively.②There was no significant differences in soil C:N ratio among Liangpan, northern Sichuan and southern Sichuan ecological zones, they were 11.25,10.08 and 10.47, respectively. While compared to the 2nd national soil survey, the C:N in three ecological zone all decreased, this situation should be promptly improved to prevent unbalanced situation become worse. The tobacco-planting soil C:P ratios in three main ecological zones were 53.78,53.99 and 54.99, and were all lower than the national average value of C:P ratio (105), it was related to the lack of SOC.The soil C:P ratios were highest in southern Sichuan, lower in northern Sichuan, and lowest in Liangpan ecological zone, While the soil AP contents exactly the opposite, this was accords with the law that C:P ratio was inversely related to the availability of P. It showed that C:P ratio had important indication action. Compared with the 2nd national soil survey, dynamic changes of soil stoichiometry in three ecological zones were decreased except P:K ratio. The P:K ratio in Liangpan ecological zone had no significant changes,while increased in northern Sichaun and decreased in southern Sichuan ecological zone. The largest reduction of C:N ratio occurred in Liangpan ecological zone, decreased by 21.00%, which was related to the excessive consumption of SOC and the enrichment and TN. The largest reduction of C:P and N:P occurred in northern Sichaun ecological zone, were 31.30% and 19.00%, respectively. Howere, the largest reduction of C:K and N:K occurred in southern Sichuan, were 21.96% and 13.33%.③In each ecological zone, the SOC was significantly correlated with TN and TP, and TN was significantly correlated with TP and TK. It indicated that SOC was the important factors that influence the soil available N, P and K contents, while SOC in three ecological zones were relatively low, so measures should be taken to add SOC.(3) The main influence factors of soil C, N, P, K and its stoichiometry characteristics of three ecological zones in Sichuan ProvinceFor each ecological zone, the main influence factors were not the same. The factors had no significant influence on C:N ratio, it remained relatively stable for different ecological zones. For Liangpan ecological zone, soil and landform types were the main influence factors of SOC and TN, and soil types were the mainly influencing factors of soil stoichiometry characteristics. However, in northern Sichuan ecological zone, the accumulated temperature mainly affected the soil AN, AK, C:P and N:P. For southern Sichuan ecological zone, soil types mainly affected TK, while accumulated temperature and altitude were the mainly influencing factors of SOC, TN and the soil stoichiometry characteristics. |
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