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

De Silva, Meragalge Swarna Damayanthi Luxmei (2007) The effects of soil amendments on selected properties of tea soils and tea plants (Camellia sinensis L.) in Australia and Sri Lanka. PhD thesis, James Cook University.

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Abstract

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.

Item ID: 2016
Item Type: Thesis (PhD)
Keywords: tea, soil amendments, tea soils, Australia, Sri Lanka, Camellia sinensis, organic mulches, Brachiaria decumbens, Calliandra calothyrsus, grass mulches, legume mulches, minplus rock dust, soil nutrients, soil fertility
Date Deposited: 16 Dec 2008 06:16
FoR Codes: ?? 079902 ??
?? 050304 ??
?? 070306 ??
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