The Oxidation-reduction Status In Tobacco-grown Soils In Yunnan Province And Tobacco Nutrition

The soil types of planted tobacco may be classified into red, purple and paddy soils in Yunnan. The tobacco with good quality is mainly originated in red soils. In the present experiment, four soils with pH values from acidic, light acidic, neutral to light alkaline were chosen to study the tobacco, an important economic crop in Yunnan, was used as the experimental crop. The treatments were chemical fertilizer and chemical fertilizer mixed with different crop straw. In tobacco growth period, oxidation-reduction potential (Eh), soil moisture content and soil microstructure were measured in root zones. At the same time, N03-N content, nutrient efficiency, nutrition and quality of tobacco were also investigated. Under the different treatments with four testing soils, the relation for the change of Eh and the status of soil nutrients and absorption efficiency of tobacco was also studied. The results obtained from two growth seasons in 1999 and 2000 in Yunnan province were shown as follows: 1. Both the yield and quality of tobacco were higher in the treatments of fertilizer mixed with crop straw than that of fertilizer applied only. Notably, the yield and income of tobacco in the fertilizer-wheat straw treatment were 17.5% and 42.8% higher than that those of fertilizer treatment, respectively. The tobacco with good and middle classes accounted for 93.2% in the treatment of fertilizer-wheat straw. 2. The rhizosphere of tobacco grown in soils was characterized by middle to good oxidation during tobacco growth. But a low Eh point was found in rapid growth period, which might be related to high root respiration and more 02 consume. However, the Eh value of rhizosphere was significantly higher in early and mature growth period than in middle period. After the application of cereal straw with high C/N ratio into soils, the Eh value in rhizosphere is significantly higher in the early growth stage, but it is lower in the late growth stage than that of the fertilizer treatments. 3. The application of cereal straw increased the soil water contents. But the statistic analysis indicated no significant co-relationship between the Eh value and water contents in rhizospheric soils. 4. Soil microstructure observation detected the decomposition of organic matter and development of structures multiply shaped which were porous. Obviously, application of crop straw benefits the improvement of soil permeability, which could result in the increment of Eh values. 5. The contents of N03-N in tobacco leaves were high in early and middle stages of growth compared to those in mature one. In the treatments of fertilizer-crop straw, the vegetative growth was promoted, the seedlings grew better and N03-N was higher in the treatments of fertilizer-crop straw than fertilizers applied only in early fast growth periods. In four experimental sites, the good growth of tobacco behaved identifiably in fertilizer-crop straw. The decrease in N03-N in the leaves benefits the maturation to produce tobacco with good quality in crop straw treatments. 6. Oxidation-reduction status in the rhizospheric soil influenced, to some extent, the absorption of nutrients by tobacco. In the treatments of crop straw, soils were oxidative and the accumulation of dry matter of tobacco was higher than that of fertilizer treatments. 7. The effect of soil Eh on the growth and qualities of tobacco was related to multiple f...