Pedoclimatic and Rice Production Factors Shaping Earthworm Distribution in Paddy Ecosystems

Abstract

Rice paddies host semiaquatic earthworms whose distribution and effects on crop performance remain insufficiently understood. This study examined the abundance and casting activity of Glyphidrilus sp. at the Chrey Bak long-term observatory in Cambodia and evaluated their relationships with pedoclimatic conditions, rice physiology, and yield. Twenty-five plots were surveyed, comprising 16 paddy fields and nine fallow or forest plots. Earthworm abundance and casting activity were monitored monthly, while soil properties, soil moisture, rice growth, leaf chlorophyll content, and yield were assessed using field and laboratory measurements. Glyphidrilus sp. was detected only in cultivated paddies during the rainy season and was absent from fallow and forest plots. Abundance and cast coverage varied seasonally, with peaks in August and November and declines during September and October. Relationships between earthworm metrics and measured soil properties were not statistically significant. Earthworm abundance was significantly and negatively associated with leaf collar height (R² = 0.35, P = 0.025). Chlorophyll content increased with earthworm abundance, although the relationship was marginally non-significant (R² = 0.27, P = 0.058). Rice yield also showed a positive but marginally non-significant relationship with earthworm abundance (P = 0.067), whereas normalised yield showed no significant relationship. Overall, the findings indicate that semiaquatic earthworm activity is closely associated with intermediate hydrological conditions, while variation in agricultural practices may obscure relationships with rice performance.