Earthworm Casting Activities under Rubber (Hevea brasiliensis) Plantations in Tripura (India)

Three different forms of casts are produced by earthworm species of rubber plantation. These are tower-like casts (Metaphire houlleti, Eutyphoeus gammiei, Eutyphoeus gigas, Eutyphoeus scutarius, Eutyphoeus assamensis, Eutyphoeus callosus, Eutyphoeus comillahnus, Eutyphoeus turaensis, Eutyphoeus sp.), composite irregular casts (Pontoscolex corethrurus, Drawida papillifer papillifer) and large globoid mounds (Kanchuria sp.1). Although the annual cast production in the rubber plantation (24 tonnes ha ) was higher than that in the mixed forest (21.3 tonnes ha ), the difference was not significant 1 1 (p>0.05). Cast production increased significantly (p<0.05) during monsoon in the mixed forest and during both summer and monsoon in the rubber plantation compared to the winter season. Organic matter content, available phosphorus and potassium, pH, electrical conductivity and water holding capacity of casts increased significantly (p<0.01) compared to the non-ingested surrounding soil in majority of the earthworm species studied. Cast production by earthworms showed significant (p<0.01) positive correlation with soil temperature, soil moisture and rainfall and week correlation with both pH and organic matter content of the soil.