Organic matter transformations and nutrient cycling in soils depend on the activity of soil
organisms. Deterioration of soil fertility lowers the biological activity and results in lower
productivity. In the absence of adequate organic matter, the processes of conversion of nutrients
to plant-available forms and their retention are very low. To enhance the activity of soil
organisms especially that of beneficial microbial populations, the addition of high quality
organic amendments is very important. Even though there are plenty of organic materials
available in tea lands, there is inadequate information on their suitability and influence on the
biological properties of soils.

The present research has attempted to determine the extent to which the microbial activity and
productivity of tea soils in Australia and Sri Lanka can be manipulated by use of readily
available soil amendments. Trials were conducted using grass and leguminous mulching
materials with different C/N ratios, in combination with two pH amendments (dolomite and
‘MinplusTM’ – a finely ground volcanic rock dust - both applied at rates of 2500 kg ha-1 only for
the pot trials and 1000 kg ha-1 for the other trials) and an inoculum of biologically active rain
forest soil. The nursery stage of tea (Camellia sinensis) propagation was studied in a
shadehouse at James Cook University, Townsville, Australia, and young tea (unpruned, 1 year
after planting) and mature tea (pruned bushes, 5 years since planting) were studied in a field in
Sri Lanka.

In the nursery trial, mulching materials consisting of finely chopped Brachiaria decumbens (a
grass), Calliandra calothyrsus (a legume), and tea prunings were applied at a rate of 35 tonnes
fresh weight ha-1 year-1 to pots with or without tea seedlings.

The grass mulch with Minplus improved soil organic carbon, CEC, soil pH, microbial biomass
carbon, plant available phosphorus, and total nitrogen contents of the soil and enhanced the
growth of plants when compared to the effects of Calliandra legume and tea mulch. All the
combinations of mulches with dolomite reduced plant growth even though they enhanced some
soil properties. Application of grass and legume mulches increased the beneficial population of
gram positive bacteria, fungi, and mycorrhiza. Grass mulch also improved the growth of tea as
measured by shoot weight and total biomass. The addition of a rainforest inoculum to the
soils of the nursery tea plants increased the soil microbial biomass carbon and growth of tea
plants even in the absence of any mulch.

The field trials in Sri Lanka demonstrated the extent of the changes induced by mulches and
soil pH modifiers in soil microbial properties, including the abundances of functional groups of
microbes (bacteria, fungi, mycorrhizae), soil microbial biomass carbon, and microbial
respiration. In addition organic carbon, soil pH, nitrogen and mulch decomposition rate were
measured. The mulching materials tested were: refuse tea (25 tonnes ha-1 year-1), Mana grass
(Cymbopogon confertiflora), and branches of Dadap (Erythrina lithosperma), a leguminous tree
(35 tonnes fresh weight ha-1 year-1). In addition to these treatments, lemon grass (Cymbopogan
nardus) 20,000 plants ha-1 as live mulch in young tea and a Trichoderma fungal culture in the
mature tea were used. For young tea and mature tea, Mana and Dadap were applied four times
and Refuse tea three times per study period and the lemon grass was planted at the start of the
trial on a 15 x 15 cm spacing in the young tea; Trichoderma was applied once to the mature tea
trial at a rate of 500 g of spore culture / plant.

The results indicated that Dadap and Refuse tea raised the yield of tea significantly by 16% and
19% respectively in young tea, and by 14% in mature tea for both mulches. The mulches
enhanced soil pH, microbial biomass carbon, soil respiration and also suppressed the most
detrimental gram negative bacterial populations one year after the application of treatments in
young tea and increased soil nitrogen by refuse tea in mature tea trial. The quality of tea
increased in tea grown under the control and lemon grass mulch treatment in young tea and in
Trichoderma fungus-treated plots in mature tea.

Minplus rock dust and the rainforest soil inoculum enhanced the growth of the nursery plants.
The most suitable mulching materials to accelerate the biological activity were found to be
those with C/N ratios below 20, and low in lignin and unoxidisable polyphenol. Therefore, the
suitable materials for use as mulches on tea lands are Brachiaria grass, refuse tea, and Dadap
legume. They also suppressed the development of pathogenic bacterial populations particularly
gram negative bacteria. These materials also improved the biological properties of soil and
thereby enhanced the growth and yield of tea.

The effects of soil amendments on selected properties of tea soils and tea plants (Camellia sinensis L.) in Australia and Sri Lanka

A series of field experiments were designed to investigate the relationship between microbial biomass nitrogen(N) and N utilization of maize in the present study.The results showed that,within the same growth period,the content of soil microbial biomass N increased with the enhanced application of this nutrient.In the different growth phase,the content of soil microbial biomass N got the highest at the seedling stage,followed by a significant reduction in jointing stage and booting stage.However,it is prone to increase during the mature phase.There was a negative correlation between microbial biomass N and the absorption amount in the different growth stage of maize.The basic content of soil microbial biomass N collaborated with N amount absorbed by seedlings(correction factor of soil available N is 96.52%),which may reflect the capacity of soil N supply.

Relationship between Microbial Biomass Nitrogen and Nitrogen Utilization of Maize

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Relationship between Microbial Biomass Nitrogen and Nitrogen Utilization of Maize