[Desorption characteristics of phosphorus in tea tree rhizosphere soil].

In order to explore the phosphorus (P) release process and its supply mechanism in tea tree rhizosphere soil, an exogenous P adsorption and culture experiment was conducted to study the P desorption process and characters in the tea tree rhizosphere soils having been cultivated for different years and derived from different parent materials. The least squares method was used to fit the isotherms of P desorption kinetics. There was an obvious difference in the P desorption process between the rhizosphere soils and non-rhizosphere soils. The P desorption ability of the rhizosphere soils was significantly higher than that of the non-rhizosphere soils. As compared with non-rhizosphere soils, rhizosphere soils had higher available P content, P desorption rate, and beta value (desorbed P of per unit adsorbed P), with the average increment being 5.49 mg x kg(-1), 1.7%, and 24.4%, respectively. The P desorption ability of the rhizosphere soils derived from different parent materials was in the order of granite > quaternary red clay > slate. The average available P content and P desorption ability of the rhizosphere soils increased with increasing cultivation years.

[Content of soil heavy metals and characteristics of environmental quality in tea plantations of Changsha Baili Tea Zone].

The distributing and changing characteristics and content of soil heavy metals was studied using methods of field survey and sampling, indoor analysis, and pollution index were used to investigate the soil environmental quality in the tea plantations of Changsha Baili Tea Zone. The results showed that the content of soil total Pb, Hg, Cd, Cr, As, Ni basically was in the soil background value, their averages were 42.7, 0.068, 0.074, 92.2, 12.4 and 19.5 mg/kg respectively. The content of heavy metals was lower than the standard of Environmental Qualification of Nuisance Free Tea Producing Area (NY 5020-2001). Simultaneity, soil environmental quality in tea plantations of Baili Tea Zone, it answered for the second grade of State Environmental Quality Standard for Soils (GB 15618-1995), achieved safe class, and the content of soil Hg, Cd, Ni accorded to the first grade of GB 15618-1995, these results showed the Changsha Baili Tea Zone were propitious to develop nuisance free tea production. Besides the single pollution index of Cr was 0.837 and in warning class at the tea plantation of Xiangfeng, the others were all less than 0.7, and in the safe class. The integrated index of 6 tea bases was all less than 0.7, in the safe class, the soil environmental quality was cleanness on the whole at Changsha Baili Tea Zone, and the soils were suitable for non-polluted agricultural production.

[Studies on the seed embryo germination and propagation of Dendrobium candidum in vitro].

OBJECTIVE: To determine optimum culture conditions for the seed embryo culture and rapid propagation of Dendrobium candidum. METHOD: Seed embryos of D. candidum were incubated in the medium containing a combination of 6-benzylaminopurine (BA) and 1-naphthaleneacetic acid (NAA), potato extract, banana extract and activated carbon in order to induce seed embryo germination, protocorm differentiation, plantlet propagation and plantlet rooting. RESULT AND CONCLUSION: The maximum embryo germination percentage was obtained in the 1/2 MS media supplemented with 20% potato extract. The 1/2 MS medium supplemented with 1.0 mg x L(-1) BA and 0.1 mg x L(-1) NAA was very beneficial to the protocorm differentiation and propagation of D. candidum. The highest protocorm propagation index was obtained from the medium containing the activated carbon. The highest root numbers and length were observed in plants growing in 1/2 MS medium containing 0.5 mg x L(-1) NAA.