Effects of inorganic and organic fertilizers on CO2 and CH4 fluxes from tea plantation soil

Agricultural practices such as fertilization considerably influence soil greenhouse gas fluxes. However, the effects of fertilization on greenhouse gases fluxes remain unclear in tea soil when soil nitrogen is low. In the present study, soil CO2 and CH4 fluxes under various fertilization treatments in tea soil were investigated during a 50-day period. The experiment consisted of five treatments: no fertilizer (CK), single nitrogen (urea, N), single oilseed rape cake fertilizer (R), nitrogen + cake fertilizer (2:1, NR1), and nitrogen + cake fertilizer (1:2, NR2). The fertilization proportion of NR1 and NR2 was determined by the nitrogen content of nitrogen fertilizer and cake fertilizer. The results revealed that the single application of nitrogen had no significant effect on soil CO2 flux. However, the addition of cake fertilizer significantly increased CO2 emissions through enhanced soil microbial biomass carbon (MBC). Additionally, CO2 emissions were directly proportional to the amount of carbon (C) in the fertilizer. All treatments were minor sinks for CH4 except for the treatment NR1. Specifically, the cumulative CH4 fluxes of NR1 and NR2 were significantly higher than rest of the three treatments, which implies that application of urea and oilseed rape cake reduced the capability of CH4 oxidation in tea soil. Structural equation models indicated that soil CO2 flux is significantly and positively correlated with soil dissolved organic carbon, MBC and soil pH, while mineral nitrogen content was the main factor affecting CH4 flux. Overall, the application of oilseed rape cake increased the oxidation of CH4 and promoted soil C sequestration but inevitably increased the soil CO2 emissions.

Potentiality of Novel Strain of Metarhizium anisopliae (Metarhizium anisopliae Strain DULS TTRA) against Odontotermes obesus, A Pest of Camellia sinensis (L.) O. Kuntze

Odontotermes obesus (Rambur) is an important termite pest of tea of North East India. The current study shows that a novel strain of Metarhizium anisopliae (Metarhizium anisopliae strain DULS TTRA, Accession no. KT 119358) a tea soil fungus is highly pathogenic to both worker and soldier caste of Odontotermes obesus in in-vitro condition. Efficacy of the experimental fungi further assessed by comparing with commercial formulation showed to have less LT50 and LC50 than the established virulent strain. We recommend the strain as a potential bio-control candidate against Odontotermes obesus.

Biocontrol studies on rizpspheric microorganisms against black rot disease of tea caused by Corticium theae Bernard

Assessment of plant growth promoter and biocontrol properties of plant growth promoting rhizomicroorganisms (PGPR) from tea soil against black rot disease agent of tea caused by Corticium theae Bernard in Bangladesh was done. The antagonistic microorganisms were isolated from rhizosphere soils of tea fields and cultured on different nutrient media. The isolates were screened for their antagonism against Corticium theae by dual culture technique. The microbial strains were inoculated with tea nursery soils by mixing with 50 g of decomposed cowdung. In tea plantations, the microbial strains were sprayed on diseased plants two times at 15 days intervals. Four different species of PGPR strains such as Bacillus, Pseudomonas, Streptomyces, Trichoderma were isolated from rhizospheric soil of tea. These PGPR strains enhanced plant growth in nursery and had a positive effect on the rate of increased in number of leaves, height of plants and girth of plants by 33, 43 and 3%, respectively. Lowest severity of black rot was found in plants treated with Trichoderma followed by Bacillus, Pseudomonas and Streptomyces strains. Trichoderma and Bacillus caused 16 and 14% reduction of disease severity while both Pseudomonas and Streptomyces strains reduced disease severity by 10%. All the PGPR’s have a great influence in reducing disease severity by 19% with optimistic relations. Radial mycelial growth of C. theae was also inhibited in similar trends. The biofertilizer showed comparatively lower response in reducing disease severity (8%) in comparison to PGPR’s. It can be concluded that Bacillus, Pseudomonas, Streptomyces and Trichoderma isolated from tea soil have their growth enhance capacity as well as decrease the disease severity of black rot in tea.