Seasonal dynamics in earthworm density, casting activity and soil nutrient cycling under Bermuda grass (Cynodon dactylon) in semiarid tropics, India

This work illustrates the result of a study on earthworm abundance, seasonal population dynamics and casting activities under Bermuda grass cover in a semiarid tropical part of Rajasthan, India. The earthworm abundance and their casting activities showed the drastic variation during different seasons. The maximum density (individual m−2) of earthworms was recorded in autumn (87.0 ± 7.2) and minimum in winter (5.3 ± 3.2) season in grassland. There was also variation in temperature and moisture of canopy soil in different seasons of the experimental year. The casting activities of earthworm also showed variations among different seasons. The maximum cast production rate was recorded during autumn (690.0 ± 78.0 g m−2) while in winter (17.3 ± 5.1 g m−2), earthworms showed the lowest cast production rate. The chemical composition of worm casts and parental soil layers (topsoil: 0–10 cm depth and subsoil: 10–25 cm depth) in grassland ecosystem was also monitored. The earthworm casts collected during winter showed the maximum level of total N (0.890 g kg−1), available P (0.373 g kg−1), exchangeable K (0.835 g kg−1), exchangeable Ca (7.10 g kg−1) and exchangeable Mg level (5.93 g kg−1) while the maximum organic C content (5.27 g kg−1) was recorded in surface casts deposited in rainy season. The level of major soil nutrients was also high in worm casts than parental soil and indicates the earthworm-mediated nutrient mineralization and organic matter transformation. Results thus clearly suggest the major role of earthworm in soil nutrient transformation in semiarid ecosystem.