Resumo -O objetivo deste trabalho foi avaliar os efeitos da compactação do solo sobre suas propriedades morfoestruturais e sobre o desenvolvimento radicular da soja, sob sistema plantio direto, em um experimento conduzido num Latossolo Vermelho distroférrico, em Londrina, PR. O delineamento utilizado foi o de blocos ao acaso, com parcelas subdivididas e quatro repetições. Foram constituídos dois tratamentos de manejo nas parcelas: um em solo escarificado à profundidade de 20-25 cm, com densidade do solo de 1,17 Mg m -3 ; e outro em solo compactado, a 12 cm de profundidade, e densidade de 1,38 Mg m -3 . Nas subparcelas, foram semeadas duas cultivares de soja, Embrapa-4 e BR-16. A presença de camadas mais compactas no perfil do solo provocou o desenvolvimento radicular em zonas de menor resistência, em poros biológicos e nas fissuras do solo. A produção de grãos não apresentou diferença entre os tratamentos, graças à adequada disponibilidade hídrica durante o período avaliado. A cultivar Embrapa-4 apresentou maior crescimento radicular em estruturas compactas, comparada à cultivar BR-16.Termos para indexação: caracterização morfoestrutural do solo, distribuição de raízes, resistência do solo à penetração. Soybean root system in function of soil compaction under no-tillage systemAbstract -An experiment was carried out on a Rhodic Ferralsol, in Londrina, PR, to evaluate the soil compaction effects on soil morphostructure and on soybean root distribution, under no-tillage system. The field experiment was arranged in a completely randomized block (split plot) design with four replicates, and with the compacted treatments in the main plots and soybean varieties in subplots. The treatments were: one scarified soil until 20-25 cm depth layer with bulk density of 1.17 Mg m -3 , and one compacted soil with bulk density of 1.38 Mg m -3 , in a 12 cm depth. Two varieties of soybean, Embrapa-4 and BR-16, were cultivated on subplots. Roots developed in zones with less resistance of penetration and in biological tunnels. The soybean grain yield was not different under compacted and noncompacted soil, because soil water moisture was adequate. Embrapa-4 showed greater root density than BR-16.
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 according to the month and the year. Survival of C. truncatum, Phomopsis spp. and C. kikuchii were significantly 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 favored 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.Index terms: cultivation, crop residues, degradation, biomass, plant diseases. Sobrevivência de patógenos em restos de cultura de soja mantidos em sistema de semeadura direta e convencionalResumo Avaliou-se a sobrevivência de patógenos em restos de soja, em sistema de semeadura direta e convencional, entre março e setembro de 1998 e 1999, em Londrina, PR. Termos para indexação: cultivo, resíduos de colheita, degradação, biomassa, doenças das plantas.
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