[Difference of rhizosphere microbe quantity and functional diversity among three flue-cured tobacco cultivars with different resistance].

Field experiments were conducted in Shilin and Xundian respectively to study the diffe- rence of rhizosphere microbe quantity and functional diversity with plate culture method and Biolog technique among Hongda (high susceptibility, S), Yun87 (middle resistance, MR) and K326 (high resistance, R) , three flue-cured tobacco cultivars with different resistance to bacterial wilt and black shank. The results indicated that the amounts of bacteria, actinomycetes and the total number of microbes in tobacco plants' rhizosphere were positively correlated with the cultivar' s re- sistance, while it was opposite for the fungi. The consistent tendency was obtained not only at 35 d, 55 d and 75 d after transplanting, but also at two experimental sites. Cultivar and experimental con- ditions greatly affected the utilization of six types of carbon source by rhizospheric microbes, as well as the AWCD value. In Xundian site, rhizospheric microbes' utilization of carbohydrates, amino acids, carboxylic acids, polymers,. amines and the AWCD value were all higher at 55 d and 75 d after transplanting for the resistant cultivar than the susceptible one, but it was opposite at 75 d after transplanting for the phenolic acids. In Shilin, significant differences existed among the three culti- vars at 35 d, 55 d and 75 d after transplanting for the indices mentioned above, although they were not consistent with cultivars' resistance. Principal component (PC) analysis even showed that utili- zation of carbon sources by rhizosphere microorganisms differed significantly among the three culti- vars at the two sites, and it was better reflected by PC1 and PC2 at 55 d and 75 d after transplan- ting, respectively. In conclusion, rhizosphere microbial community structure and functional diversity were greatly affected not only by the cultivars' difference in resistance, but also by experimental conditions.

[Nutrient balance between N, P, and K in flue-cured tobacco production under different preceding crops planting].

A field experiment was conducted to study the nutrient balance between N, P, and K in flue-cured tobacco production in Shilin County of Yunnan Province under the effects of different preceding crops including rape, wheat, barley, and green manure planting. Overall, there existed significant differences in the soil nitrogen availability, tobacco plant dry matter accumulation, plant uptake of N, P and K, residual amounts of soil N, P, and K, apparent soil N loss, and apparent soil P- and K surplus during tobacco growth period under different preceding crops planting. Under preceding crop green mature planting, the soil mineral N content before tobacco plant transplanting, the soil N net mineralization rate during tobacco growth period, and the tobacco plant dry matter accumulation and N- and K uptake at maturation were all the highest, followed by under preceding rape planting, and under preceding barley or wheat planting. The P uptake by tobacco plant was also obviously higher under the preceding green manure or rape planting than under preceding barley or wheat planting. After the harvest of tobacco leaves, the soil residual mineral N content was the highest under the preceding green manure planting, followed by under preceding rape planting, and by preceding barley or wheat planting, while the soil available P and K contents were in adverse, being the highest under preceding barley or wheat planting and the lowest under preceding green manure planting. The apparent soil N loss during tobacco growth period was the highest under the preceding green manure planting, whereas the apparent soil P- and K surplus was obviously higher under preceding wheat or barley planting. It was suggested that an appropriate adjustment should be made on the fertilization rates of N, P, and K for tobacco production based on the preceding crops, i. e., lesser N application when the preceding crop was green manure or rape, and lesser application of P and K when the preceding crop was wheat or barley.