Eleno Torres

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

Summary 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 × 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 (16‐42 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.

Survival of pathogens on soybean debris under no-tillage and conventional tillage systems

n†A study was conducted in the subtropical area of Southern Brazil to determine the survival of pathogens in soybean residues under conventional and no-tillage cultivation systems from March to September of 1998 and 1999. The pathogens most frequently isolated were Colletotrichum truncatum, Phomopsis†spp., Cercospora kikuchii, Fusarium†spp., Macrophomina phaseolina, and Rhizoctonia solani. Other fungi isolated were Myrothecium roridum, Penicillium†sp., Chaetomium sp., Epicoccum†sp., Corynespora cassiicola and Trichoderma†sp. The percent of survival of each pathogen varied accord- ing to the month and the year. Survival of C.†truncatum, Phomopsis†spp. and C.†kikuchii were signifi- cantly reduced (p<0.05) from the first to the last evaluation either on buried debris or maintained on the soil surface. On†the other hand, M.†phaseolina and Fusarium†spp. were either not affected or fa- vored by burying the debris. The frequency of recovery of Fusarium†spp. increased specially in debris kept under the soil. The loss of biomass, measured by debris weight along the period of this study, showed a reduction of 44.4% in the conventional system and 34.9% in the no-tillage system in†1998, when rain was better distributed. In 1999, the reduction was 48.2% and 39.0% for the conventional and no-tillage system, respectively.

Progress of soybean charcoal rot under tillage and no-tillage systems in Brazil

The increase in incidence of charcoal rot caused by Macrophomina phaseolina on soybeans (Glycine max) was followed four seasons in conventional and no-till cropping systems. In the 1997/98 and 2000/01 seasons, total precipitation between sowing and harvest reached 876.3 and 846.9 mm, respectively. For these seasons, disease incidence did not differ significantly between the no-till and conventional systems. In 1998/99 and 1999/00 precipitation totaled 689.9 and 478.3 mm, respectively. In 1998/99, in the no-till system, the disease incidence was 43.7% and 53.1% in the conventional system. In 1999/00 the final incidence was 68.7% and 81.2% for the no-till and conventional systems, respectively. For these two seasons, precipitation was lower than that required for soybean crops (840 mm), and the averages of disease incidence were significantly higher in the conventional system. The concentration of microsclerotia in soil samples was higher in samples collected in conventional system at 0 - 10 cm depth. However, analysis of microsclerotia in roots showed that in years with adequate rain no difference was detected. In dry years, however, roots from plants developed under the conventional system had significantly more microsclerotia. Because of the wide host range of M. phaseolina and the long survival times of the microsclerotia, crop rotation would probably have little benefit in reducing charcoal rot. Under these study conditions it may be a better alternative to suppress charcoal rot by using the no-till cropping system to conserve soil moisture and reduce disease progress.

Matéria seca, carbono e nitrogênio de raízes de soja e milho em plantio direto e convencional

The objective of this work was to examine whether soil tillage systems affect the distribution and accumulation of dry matter (DM), carbon (C) and nitrogen (N) of root systems of soybean (Glycine max) and corn (Zea mays) in a clayey Typic Haplorthox. Volumetric rings were used for root sampling down to 1 m depth. The distribution in depth and accumulation of DM, C and N of soybean and corn roots were not affected by soil tillage systems. Root length density was 0.7-1.4 cm cm-3 for soybean and 1.2-1.6 cm cm-3 for corn in the 0-0.10 m layer and decreased in the other layers. Root DM input was 1.94-2.01 Mg ha-1 in soybean and 2.50-3.79 Mg ha-1 in corn. For soybean, C and N root inputs were 0.61-0.63 Mg ha-1 and 36.9-38.2 kg ha-1, respectively. For corn, C and N root inputs were 0.72-1.10 Mg ha-1 and 18.78-28.48 kg ha-1, respectively. Independently of the tillage system, 80% of the roots were concentrated in the upper surface layer 0.43 to 0.54 m deep for soybean and in the upper surface layer 0.40 to 0.46 m deep for corn.

BENEFIT OF LEGUME-FIXED N IN CROP ROTATIONS UNDER ZERO-TILLAGE

Under conventional tillage, although the contribution of BNF to soybean was high (190–315 kg N ha −1 ), more N was removed in the grain, resulting in a negative balance. Under no-tillage, the N balance was occasionally slightly positive. In the case of lupins, as no N was harvested from the system, there was a large N contribution to the subsequent maize crop. The no-till system favoured the retention of soil N and a higher BNF contribution to the legumes.