No-tillage greatly increases earthworm populations in Parana state, Brazil

摘要

No-tillage (NT) agroecosystems now occupy >18 million ha in Brazil, of which 5 million are in the state of Parana, where NT began in the early 1970's. The first NT farmers created an association to promote their practices, the 'Clube da Minhoca' (Earthworm Club), thus named because of the observed increase in earthworm numbers in their fields after adopting NT However, little data were available on the topic until 1996, when more intensive studies began near Londrina, in N Parana. Earthworms were sampled by hand-sorting soil monoliths (25 x 25 cm square, 30-40 cm depth) at 8 sites, comprising various natural and agricultural land-use and management systems. Data from the literature were collected from a further 6 sites for comparative purposes. The results for N Parana confirm the presence of higher earthworm populations under NT (46-116 indiv., 0.49-1.06 g f.wt. m(-2); mean values in dry-wet seasons, respectively), minimum tillage (42-179 indiv., 0.68-1.05 g f.wt. m(-2)), pastures (48-182 indiv. m(-2)) and native forests (116-42 indiv., 1.56-0.83 g f.wt. m(-2)) than under conventional tillage (13-22 indiv. and 0.13-0.02 g f.wt. m(-2)). Soil disturbance thus had a negative impact on earthworm populations, and significant positive relationships were observed between earthworm abundance and age of NT systems, as well as with soil % C. In the Londrina area, some species present in the primary forests were absent in NT, where most earthworms were small-sized endogeic or epi-endogeic species. These results contrasted greatly with those from the cooler region in E Parana, where the exotic epi-endogeic Amynthas spp. dominated, reaching high densities (up to >100 indiv. m(-2)) and biomass (up to >30 g f.wt. m(-2)), especially under NT Given the high abundance of worms under NT, further work should focus on estimating their potential contributions to soil processes, fertility and plant production in these systems.