Regional Difference In Organic Matter In Tobacco Soils In Hunan Province And Relations Between It And Mineralization Of Soil Organic Nitrogen

The regional differences of Tobacco-growing soil organic matter (O.M.) had obvious variation in Hunan, but the contents of different soil O.M. had little effects on the growth of flue-cured tobacco. In order to find the reasons, the regional differences of soil O.M. and the mineralization characteristics of soil organic nitrogen in different ecological conditions were analyzed, and the relationships between soil O.M. components and soil organic nitrogen mineralization were also studied. Furthermore, the effect of the soil active organic carbon (SAOC) on nitrogen supply was probed. Pot experiments were conducted to study the dynamics of soil O.M. components under different ecological conditions and the relationships between dry matter and nitrogen absorption of flue-cured tobacco during growing stages. The main results obtained were as follows:Soil O.M. content ranged from 17.2 to 53.3 g·kg^-1, the average of O.M. was 33.8 g·kg^-1 Soil O.M. was the highest in the southern of Hunan with average O.M. 43.1 g·kg^-1, followed by the middle of Hunan with average O.M. 31.9 g·kg^-1 and in the western of Hunan with average O.M.23.9 g·kg^-1 was the lowest. Soil O.M. had a significant difference at different tobacco production areas. There were very significant difference between the southern and western of Hunan.Soil O.M. was raised gradually from the west to the southern of the research areas. Soil humus carbon content was in the range of 4.7⁵.1 g·kg^-1, and there was no obviously difference under different tobacco production areas. The difference of soil non-humus carbon content was significant and its content varied from 13.3 to 25.9 g·kg^-1There was no obviously difference between humic acid carbon content and Humic acid / Fulvic acid ratio. The SAOC ranged from 2.6 to 6.5 g·kg^-1 and the average content was 3.87 g·kg^-1 The SAOC was the highest in the southern of Hunan with average SAOC 4.6 g·kg^-1 followed by the middle of Hunan with average SAOC 3.8 g·kg^-1, and in the western of Hunan with average ASOC 3.6 g·kg^-1 was the lowest, but it had no significant effect on different regional areas. There was significant difference of proportion of SAOC to total organic carbon.The correlation between SAOC content and humus, humic acid and soil O.M. was very significant. And the correlation coefficient R²= 0.628^** between ASOC and humus. It suggested that most of SAOC was highly active humus. But there were not obvious relationship between soil O.M. and humus content. The content of soil O.M. can not respond the effect and contribution to the soil nutrient by organic matter completely. So the ASOC was one of most important factors on the growth of flue-cured tobacco.Whether non-till or planting, there were not significant effect on the total content of Tobacco-growing soil O.M. without adding extra organic materials. Roots activity promoted humus accumulation, but the effect was not significantly different. The difference and of the soil O.M. mineralization were also related to...