EARTHWORM CASTING ACTIVITY AND THEIR NUTRIENT CONTRIBUTION TO THE SOILS OF PASTURE, NATURAL FOREST AND RUBBER PLANTATION IN TRIPURA INDIA

Present study revealed casts of a total of 9 earthworm species (Eutyphoeus assamensis, E. comillahnus, E. scutarius, E. gigas, Lampito mauritii, Kanchuria sp., Metaphire houlleti, Pontoscolex corethrurus and Glyphidrilus sp.) from three land-use systems (pasture, natural forest and rubber plantation) of West Tripura and Sepahijala districts of Tripura, India. Different species of earthworms voided casts in different forms i.e. granular, globular or tower like. Strong positive correlation was found between earthworm body weight and diameter of casts (r = 0.68, P = 0.01). Among the three studied ecosystems, natural forest had the highest annual casts production of 23.44 tonnes ha-1 year-1. On the other hand pasture and rubber plantation exhibited an annual cast production of 11.16 tonnes ha-1 year-1 and 9.92 tonnes ha-1 year-1 respectively. Out of 9 earthworm species, E. assamensis, P. corethrurus and L. mauritii contributed the highest annual cast production of 8.44 tonnes ha-1year-1, 6.65 tonnes ha-1year-1 and 5.00 tonnes ha-1year-1 under natural forest, rubber plantation and pasture respectively. Significant positive correlation was observed between cast production vs. rainfall (pasture: r = 0.59, P < .05; natural forest: r = 0.48, P < .05; rubber plantation: r = 0.69, P < .05), cast production vs. temperature (pasture: r = 0.51, P < .05; natural forest: r = 0.54, P < .05; rubber plantation: r = 0.52, P < .05) and cast production vs. moisture (pasture: r = 0.59, P < .05; natural forest: r = 0.62, P < .05; rubber plantation: r = 0.66, P < .05). The peak of cast production in earthworm species coincided during the monsoon period in our present study. Analysis of physical properties of earthworm casts and its surrounding soils revealed that casts had a significantly (P < .05) higher pH and moisture values compared to non-ingested soils. The chemical analysis of earthworm casts revealed that casts were significantly (P < .05) rich in organic C, as well as, in total N, av. P and av. K compared to their surrounding soils.