Effect of the endogeic earthworm Pontoscolex corethrurus on soil chemical characteristics and plant growth in a low-input tropical agroecosystem

Low densities of #Pontoscolex corethrurus$ have been introduced into low-input cropping systems at Yurimaguas (Peru) to test their effects on soil fertility under field conditions for six succesive cropping cycles. Earthworm biomass was sustained at 40 g/m2 fw (ca. 3 g ash-free dry mass) on the average with peak values of 80 g at harvests 2 and 3 in treatments receiving an application of legume green manure. At the 6th harvest, earthworm biomass was significantly lower in the treatment with no organic input than in treatments with crop residues and legume green manure. Earthworm activities did not prevent C and nutrient stocks from being significantly depleted although P, K and Ca concentrations tended to be higher than in non-inoculated treatments at the 6th harvest. Plant production was significantly increased by 36% due to earthworm inoculation in a traditional low-input rotation (maize, rice, cowpea, rice, rice, rice) with variation between -43 and +78%, depending on the crop and climatic conditions. In a continuous maize culture that received fertilizers for the last three crops, grain production was increased by 2.45-fold on average, due to earthworm inoculation. These results demonstrate that the maintenance of active earthworm populations was favourable to crop production during the time scale of our experiments (3 y). Longer term experiments are required to test the sustainability of the positive effects observed. (Résumé d'auteur