6th international symposium on earthworm ecology

A green house experiment was performed using the radioisotope 32P to study the effects of earthworms (#Pontoscolex corethrurus$) and P fertilization on #Brachiaria decumbens$ pasture production and P dynamics in a P-limited soil from a pasture in Veracruz, Mexico. Two fertilization levels (0 and 10 kg/ha P) were applied, while the soil P pool was labelled with 10mg 32P/pot (equivalent to 1.6 kg P/ha). At harvest (51d) measurements included shoot and root biomass, total, inorganic, organic and exchangeable P in the soil and earthworm castings, mycorrhizal infection in roots, and earthworm populations. Fertilization with 10 kg/ha (injected P) increased shoot biomass by almost 10 times and root biomass by three times. Earthworms were only important for biomass production and P uptake with 10 kg/ha P, where despite significant yield reductions, more 32P fertilizer was imported into plants and the coefficient of 32P fertilizer use was significantly higher. On the other hand, treatments with earthworms tended to have lower organic P and higher available-P contents. Both fertilization and earthworms had a significant negative effect on root infection by VAM. Total P contents of earthworms was high (0.4%), and 32P derived from the fertilizer reached from 3 to 4% of the total at harvest. Earthworm castings were richer in total P and especially organic P, than uningested soil. By ingesting soil rich in organic P, producing large amounts of castings (P-rich microsites), and stimulating P mineralization processes in soils, #P. corethrurus$ forms an important component of the soil P cycle, and further research should pay attention to their potential as priming agents within the soil, and their effects on plant growth and nutrient uptake. (Résumé d'auteur