Physico-chemical and biological properties of high evaluation soils with reference to tea (Camellia sinensis)

Abstract

A study has been made on the Tea plantations in Ponmudi in Kerala State with a view to determine the extent to which the physical, chemical and biological characters of these soils are affected by the plantation. Samples for the study were collected from soil profiles exposed at different locations in the tea and adjacent non – tea areas. Plant samples were also collected from these locations and subjected to detail chemical analysis. The mechanical composition of the soils of tea plantations did not depict any significant difference when compared to non – tea soils. In both these soils, the sand and silt content decreased, and clay content increased with depth in the profile. However, a higher content of clay observed in the tea soils indicates a greater degree of weathering and clay formation. The bulk density and particle density of the tea and non – tea soils increased with depth. The surface soil of the profile which contained a greater amount of organic matter recorded a higher water holding capacity. The CEC of soils was found to be low and is likely to be influenced by the predominance of kaolinitic clay minerals. The soils of the tea plantations were highly acidic. Exchangeable aluminium and hydrogen which are the factors contributing to soil acidity were more or less similar in the tea and non – tea soils. The tea plantation recorded a highercontent of total and available nitrogen compared to non – tea areas. The soils cultivated to tea, though contained only a lower amount of total phosphorous, registered a higher content of available phosphorous. The high content of phosphorous is apparently due to the annual application of heavy doses of phosphatic fertilizers. Total acidity, sesquioxides and clay content were higher in the tea soils and contributed to a greater P fixing capacity. The contents of total and exchangeable potassium as well as exchangeable calcium and magnesium in soils cultivated to tea were higher than the adjacent non – tea soils. Lack of fixation sites for potassium in the tea soils might have probably lead to a higher status of exchangeable potassium. The total microbial count including that of bacteria, fungi and actinomyctes in the tea and non – tea areas was appreciable. The tea soils possesed a higher capacity for solubilisation of insoluble inorganic phosphates which was related to the total acidity. These soils did not show any capacity for nitrogen fixation and urease activity was comparatively low. Chemical analysis of the tea leaves showed a higher content of nitrogen and phosphorous than other nutrient elements. The annual application of fertilizers and a lesser removal of nutrients through processed tea has resulted in a rather high fertility status of the tea soils.