Tea Rhizosphere Research Articles

Effect of forms of nitrogen supply on mobilisation of phosphorus from a phosphate rock and acidification in the rhizosphere of tea

Nitrogen (N) is the main fertiliser input to tea plantations because of the large removal of this element with regular harvests of young shoots in the field. The form of N supply is known to influence the uptake of other plant nutrients, notably phosphorus (P), through its effect on soil pH in the rhizosphere. A glasshouse study was conducted to test the effect of N form (NH +4, NO-3 , or both) on the transformation of soil P in the rhizosphere and its availability to tea (Camellia sinensis L.) plants fertilised with sparingly soluble Eppawala phosphate rock (EPR). Four-month-old tea (TRI 2025) plants were grown in rhizosphere study containers containing an Ultisol from Sri Lanka (pH 4 ·5 in water) amended with EPR and KCl at 200 g P or K/g soil, and mixed with (NH4)2SO4 (100% NH+4 -N), NH4NO3 (50% NH+4 -N and 50% NO-3 -N), and Ca(NO3)2 (100% NO-3 -N) at the rate of 200 g N/g soil, with a control (no N fertiliser), as treatments. Rhizosphere pH decreased compared with the bulk soil when N was supplied as NH+4 or NH+4 +NO-3 forms, and increased when N was supplied as NO-3. The cation{anion balance estimations in the plants showed that the plants had taken up more NO-3 than NH+4 even in (NH4)2SO4 treated soil, suggesting high nitrification rates, especially in the rhizosphere, in spite of using a nitrification inhibitor. More EPR dissolved in the rhizosphere compared with that in the bulk soil, regardless of the N form applied. The (NH4)2SO4 treatment had the highest dissolution rate of EPR in the rhizosphere, whereas Ca(NO3)2 treatment had the lowest, reflecting the degree of acidification in the rhizosphere. Resin-P and NaOH-Pi (inorganic P) concentrations were lower and NaOH-Po (organic P) concentration was higher in the rhizosphere than in the bulk soil. Plant and possible microbial uptake of P is the main reason for the decrease in resin-P and NaOH-Pi. The increase in NaOH-Po concentration in the rhizosphere is believed to be due to transformation of Pi to Po by the high microbial activity in the rhizosphere. The (NH4)2SO4 treatment caused the highest depletion of resin-P but lowest depletion of NaOH-Pi, probably due to the fixation of P by the soils at the low pH in the rhizosphere. The study revealed that the use of the NH+4 form of fertiliser can increase acidification in tea rhizosphere compared with bulk soil and this can enhance the effectiveness of PR fertiliser utilisation by tea plants.

Antifungal activity of bacteria isolated from the rhizosphere of established tea bushes

A large number of bacteria and fungi were isolated from the rhizosphere of established tea bushes, by serial dilution technique, over a period of one year. Fifty one of these bacterial isolates were tested for their antifungal activity against twelve test fungi, which included nine minor (saprophytes) and three major pathogens of tea. Following preliminary screening, nine bacterial isolates were selected and their antifungal activity was further investigated. Based on colony characteristics, morphological & biochemical properties, a preliminary classification of these bacterial isolates has been carried out. Isolate no. 1 was tentatively identified as Bacillus mycoides; the remaining eight strains which also appear close to the genus Bacillus, differed in their antagonistic reaction. The bacterial isolates exhibiting highest antifungal activity were also the most dominant bacterial species in the tea rhizosphere.

A comparison of some techniques for the isolation of fungi from tea soils.

The fungal flora of tea soils from Tocklai was analysed using dilution plate method, Rossi-Cholodny's slide technique, direct inoculation, Warcup's soil plate method and the washed root technique. By all the methods a total of 123 species of fungi comprising 67 genera was isolated; washed root method alone yielding 85 species followed by Warcup's soil plate method. In view of the great diversity of fungal species occurring in the rhizosphere of tea, their possible role in the mycorrhizal association and their importance in investigations on the biology of tea root rot pathogens is indicated.