Phosphorus in soil and Brachiaria decumbens plants as affected by the geophagous earthworm Pontoscolex corethrurus and P fertilization

A greenhouse experiment was performed using the radioisotope P-32 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 h a(-1) P) were applied, while the soil P pool was labelled with 10mg P-32 po t(-1) (equivalent to 1.6 kg P ha(-1)). At harvest (51d) measurements includ ed shoot and root biomass, total, inorganic, organic & exchangable P in the soil and earthworm castings, mycorrhizal infection in roots, and earthworm populations. Fertilization with 10 kg ha(-1) (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(-1) P, wh ere despite significant yield reductions, more P-32 fertilizer was imported into plants and the coefficient of P-32 fertilizer use was significantly h igher. On the other hand, treatments with earthworms tended to have lower o rganic P and higher available-P contents. Both fertilization and earthworms had a significant negative effect on root infection by VAM. Total P conten ts of earthworms was high (0.4 %), and P-32 derived from the fertilizer rea ched 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 soi l rich in organic P, producing large amounts of castings (P-rich microsites ), and stimulating P mineralization processes in soils, P. corethrurus form s an important component of the soil P cycle, and further research should p ay attention to their potential as priming agents within the soil, and thei r effects on plant growth and nutrient uptake.