摘要：Population dynamics of earthworms in the two different cultivable land areas – wet land cultivable areas (WLCA) (including paddy, banana and sugarcane fields) and dry land cultivable areas (DLCA) (including coconut and groundnut fields) of five different pedoecosystems in the Cauvery delta areas of Sirkazhi taluk, Nagapattinam district, Tamil Nadu state, India with reference to various soil ecological parameters have been studied, for the first time during the period from November 2011 to April 2012. The WLCA (paddy> sugarcane> banana fields) harbor maximum population dynamics of earthworms whereas low in DLCA (groundnut> coconut fields). This may be due to presence of more edaphic factors - OC, N and moisture. Along with these, microorganisms as protein and N rich food support for earthworm growth and reproduction. They are involved synergistically influence the density and biomass of earthworm at maximum. In the five different pedoecosystems of Cauvery delta areas, only two types of soil namely clayloam and sandyloam are found and this variations are due to the nature of earlier agricultural activity and the nature of soil texture. Population dynamics of earthworm in different pedoecosystem are found in soil having 17.6–23.8% range of moisture and among pedoecosystems, more moisture content and more earthworm population dynamics are found in paddy field, followed by sugarcane, banana, groundnut and coconut field. This is due to adequate and frequent irrigation, more water holding capacity, higher microbial activity, OC, N and other nutrient content of the soil. In the five different pedoecosystems, are found in soil having 17.3 – 18.5C ranges of temperature. This indicates the ideal and optimal temperature for earthworm survival and reproduction in these areas. The population dynamics of earthworm are found within a narrow range of pH (6.7 – 7.3) and this variations of soil pH within these delta areas are due to the variation of salinity and acidity nature of the soil. The higher occurrence of maximum density and biomass of earthworms at WLCA as compared to DLCA is supported by higher OC (62-69%) of the soil of different pedoecosystems. The C:N ratio recorded in WLCA ranges from 2.09 to 2.21 and in DLCA ranges from 2.7 to 4.9. This indicate the adequate level of C and N in the soils of different cultivable land areas that support for the survival, distribution, abundance and density of earthworms. The WLCA are found to shows more N, P and K content than DLCA. This is due to the naturally available nutrient contents of soil/optimal moisture/soil input of organic materials during agricultural activity/enhanced nutrient mineralization by the earthworm – microbe symbiosis and enhanced microbial activity. Among the two different cultivable areas, more microbial activity are found in the WLCA than DLCA. This indicate the presence of optimal moisture, more OC, N and microbial population. Finally, it may be suggested that the synergistic effect of soil ecological parameters, even though both positively or negatively correlated with each others of different pedoecosystem of Cauvery delta areas had more influence on population dynamics of earthworms.
