Effects of the earthworm Pontoscolex corethrurus on rice P nutrition and plant-available soil P in a tropical Ferralsol

Abstract

We conducted a greenhouse experiment in mesocosms for 28 days to assess the effects of the endogeic earthworm Pontoscolex corethrurus on plant-available soil phosphorus (P) and rice ( Oryza sativa ) P nutrition in a Malagasy Ferralsol. To assess plant-available soil P, we determined the L-value by measuring the specific activity of P taken up from the soil by rice and by applying the isotopic dilution principle. Despite earthworm mortality, P. corethrurus significantly increased rice shoot biomass (+26%) and P nutrition (+65%), confirming that the soil used for the experiment was P-deficient. The L-value also markedly increased from 6.8 ± 0.9 to 14.2 ± 1.3 mg P mesocosm −1 in the presence of P. corethrurus . We estimated that the orthophosphate ions released due to earthworm mortality contributed to 30% of the L-value increase. We attributed the remaining 70% increase to the solubilization of native soil P during its transit through the digestive tract. Thereafter, we discussed the sources of uncertainty associated with the L-value calculation and their utilization to assess earthworm effects on P availability in further studies. • We assessed the effects of P. corethrurus ( Ponto ) on plant-available soil P. • Ponto increased rice shoot biomass (+26%) and P nutrition (+65%). • The L -value raised from 6.8 (±0.9) to 14.2 (±1.3) mg P cosm −1 in presence of Ponto . • The P release due to Ponto mortality contributes to 30% of the L -value increase. • The relevance of using L -value in earthworm inoculation experiments is discussed.