Natural abundance of 13C and 15N in earthworms from different cropping treatments

In order to get a better understanding of soil fauna responses to land use changes we used an experimental design established in Devon (UK) and selected five replicated treatments: maize (C-4 plant), grass (C-3 plant), clover (C-3 plant fixing N from the air) and two bicropping systems consisting of maize with a clover understorey. Soil and earthworm samples were taken from each treatment in two sampling occasions (July and October 1998). Results showed that in all treatments the highest C and N contents were measured in the top 10 cm of the soil, with the exception of the maize plots possibly as result of recent rotavation. In contrast soil delta values increased with depth suggesting that agricultural practices affect the distribution of the organic matter through the soil profile. Isotopic composition of the earthworms showed that they were also significantly affected by the cropping systems. In agreement with previous findings N isotope values seem to be related to ecological groupings and ontogenic changes. Furthermore, under bicropping systems endogeic worms seem to gain their nutrition from older residues which is also in correspondence with their vertical distribution in the soil.