RESUMO Experimentos de campo foram executados durante a primavera de 2014 e outono e primavera de 2015 para determinar o efeito de cobertura verde no desenvolvimento da epidemia de Phytophthora infestans, no município da Lapa, Estado do Paraná, região Sul do Brasil. As cultivares usadas foram ’Agata’, suscetível, e ‘BRS Ana’, moderadamente suscetível. O principal tratamento consistiu da aplicação manual de uma camada de aproximadamente 10 cm de espessura, com material vegetal recém-colhido (cobertura verde), quando os brotos de batata estavam emergindo. O material para a cobertura verde era o disponível para a época do ano. Para os experimentos de primavera, foi utilizada uma mistura de aveia, centeio e nabiça (60 t/ha) e para os de outono, capim elefante em final de ciclo (90 t/ha). As parcelas consistiram de seis linhas de 10 m, espaçadas de 0,8 m, 28 plantas por linha. O delineamento experimental foi de parcelas pareadas em blocos casualizados, com quatro repetições. Confiou-se em inoculação natural. A porcentagem da área foliar foi estimada semanalmente até o final do ciclo das plantas e a área sob a curva de progresso da doença (AUDPC) foi calculada. A aplicação de cobertura verde reduziu significativamente a AUDPC em 32,1, 12,4 e 23,1%, comparando-se ao controle, em todas as safras para ‘BRS Ana’, e em 26,1, 2,8 e 12,0% para ‘Agata’. O uso de cobertura verde mostrou-se uma prática promissora para entrar no manejo integrado da requeima e proteger a produtividade, especialmente nos períodos mais favoráveis ao desenvolvimento da doença. Mais estudos detalhados devem ser continuados sobre o tipo de plantas, quantidade de cobertura verde a ser usada e a possibilidade de redução da dose ou aumento do intervalo de pulverizações com fungicidas.

ABSTRACT Field experiments were conducted during spring 2014 and fall and spring 2015 to determine the effect of fresh mulch on the development of Phytophthora infestans epidemics, in Lapa Municipality, Parana State, southern Brazil. The used cultivars were ‘Agata’, susceptible, and ‘BRS Ana’, moderately susceptible. The main treatment consisted in manually applying a 10cm-thick layer of fresh mulch when potato sprouts were emerging. Fresh mulch was prepared with plants available at that time of the year. For the spring experiments, fresh mulch was a mixture of oats, rye grass and wild radish (60 t/ha) and for the fall experiment, semi-ripe elephant grass (90 t/ha). Plots consisted of six 10m-long rows, spaced at 0.8m, containing 28 plants per row. Experimental design was in completely randomized blocks with four replicates. Natural inoculum was adopted. Percentage of leaf area was weekly estimated until the end of the plant cycle and the area under the disease progress curve (AUDPC) was calculated. Application of fresh mulch significantly reduced AUDPC by 32.1%, 12.4% and 23.1%, compared to control in all seasons, for ‘BRS Ana’ and by 26.1%, 2.8% and 12.0% for ‘Agata’. Application of fresh mulch showed to be a promising practice for the integrated management of late blight and for the protection of yields, especially in periods more favorable to the development of the disease. More detailed studies should be conducted on the plant type and amount of fresh mulch to be used, as well as on the possibility of reducing concentrations or increasing intervals between fungicide sprays.

ABSTRACT Soil management and crop rotation are key factors in controlling the accumulation of C and N in the soil profile, but their long-term effect remains poorly understood for deep soil layers, especially in subtropical conditions. Using a long-term experiment (26-years), this study aimed to evaluate the effect of different soil management systems associated with different winter cover crops on C and N accumulation in a very clayey (72 % clay) soil up to 1 m deep. Two tillage systems [conventional tillage (CT) and no-tillage (NT)] were cultivated with eight winter cover crops (black oat, rye, common vetch, hairy vetch, oilseed radish, wheat, blue lupine, and fallow) in a subtropical Oxisol from Southern Brazil. Soil samples were taken in eight soil layers up to 1.00 m soil depth after 26 years of experiment and, also from an adjacent native forest. After forest clearing, the C stock in the 0.00-0.20 m soil layer was reduced by 45 % in only 10 years (from 1976 to 1986) of soil tillage. Twenty-six years after the beginning of the experiment, C and N stock in 0.00-0.20 m soil layer were 13 and 20 % higher in NT compared to CT, with the greatest differences in C and N content observed in the 0.00-0.05 m layer. When associated with winter cover crops, NT accumulated 0.6 and 0.06 Mg ha-1 yr-1 more C and N than CT with winter fallow in the 0.00-0.20 m soil layer. No-tillage and CT recovered 95 and 83 %, respectively, of the C stock found in the 0.00-0.20 m layer from the native forest. However, in the 0.00-1.00 m soil layer, the positive effect of NT on soil C accumulation compared to CT was diluted, and no clear effect of NT was verified. Moreover, no difference in winter cover crops on soil C and N stocks were observed in all soil layers, possibly due to their similar residues input (3.3-4.9 Mg ha-1 yr-1). No-tillage associated with high biomass input through winter cover crops promoted a faster recovery of soil C and N stock than in CT and, therefore, is an efficient tool to improve soil C and N accumulation even in Oxisols with high clay content.