No abstract

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is one of the most destructive fungal diseases affecting soybean production. Silicon (Si) amendments were studied as an alternative strategy to control SBR because this element was reported to suppress a number of plant diseases in other host–pathogen systems. In greenhouse experiments, soybean cultivars inoculated with P. pachyrhizi received soil applications of wollastonite (CaSiO3) (Si at 0, 0.96, and 1.92 t ha–1) or foliar applications of potassium silicate (K2SiO3) (Si at 0, 500, 1,000, or 2,000 mg kg–1). Greenhouse experiment results demonstrated that Si treatments delayed disease onset by approximately 3 days. The area under disease progress curve (AUDPC) of plants receiving Si treatments also was significantly lower than the AUDPC of non-Si-treated plants. For field experiments, an average 3-day delay in disease onset was observed only for soil Si treatments. Reductions in AUDPC of up to 43 and 36% were also observed for soil and foliar Si treatments, respectively. Considering the natural delayed disease onset due to the inability of the pathogen to overwinter in the major soybean production areas of the United States, the delay in disease onset and the final reduction in AUDPC observed by the soil Si treatments used may lead to the development of SBR control practices that can benefit organic and conventional soybean production systems.

RESUMO: A presença de camada compactada próxima à superfície do solo e a variabilidade das propriedades químicas do solo podem afetar o rendimento de grão de soja. Com o trabalho, objetivou-se avaliar a influência de sistemas de preparo do solo e de semeadura e de locais de cultivo (áreas de corte e aterro) no rendimento dessa cultura. O experimento foi realizado na área experimental de várzea da Universidade Federal de Santa Maria, nas safras 2013/14 e 2014/15. O delineamento foi blocos ao acaso, com quatro repetições. Os tratamentos foram arranjados em parcelas subdivididas. As parcelas principais foram: área de corte (A1) e área de aterro (A2). As subparcelas foram os tipos de preparo do solo e de semeadura: com escarificação do solo e semeadura utilizando disco duplo na semeadora (D1); sem escarificação do solo e semeadura utilizando haste sulcadora na semeadora (D2); sem escarificação do solo e semeadura utilizando disco duplo na semeadora (D3). A cultivar utilizada foi a BMX Tornado. O tratamento com escarificação e haste sulcadora reduziu a resistência do solo à penetração e proporcionou maior teor de Mg e S no tecido foliar na safra 2013/14; e de N, P, K, Ca, Mg e S, em 2014/15. Esse tipo de preparo de solo possibilita maior rendimento de grão de soja sem diferenças entre as áreas de corte e de aterro.

Silicon (Si) affects the susceptibility of plants to fungal attack. In plants with low Si accumulation, disease-control mechanisms involve the accumulation of phenolic compounds and Si. This study compared the effects of calcium silicate and carbonate doses on the control of soybean (Glycine max) diseases. A sandy soil was collected from Santa Vitória, Minas Gerais state, Brazil, of which 200 kg was placed in plastic drums in a protected, uncovered area. Calcium carbonate or silicate was applied superficially in amounts equivalent to 0, 1500, 3000, 6000, or 12,000 kg ha −1 , and soybean was cultivated for 120 d. Leaf Si concentration and incidence of Cercospora sojina (Frog's eye spot), Peronospora manshurica (downy mildew), and Phakopsora pachyrhizi (Asian rust) were evaluated. Calcium carbonate did not reduce disease incidence; however, calcium silicate was effective in the reduction of downy mildew at 47 and 66 d after soybean seeding, and of frog's eye spot incidence at all dates evaluated. Asian rust was observed only at 79 d after seeding and calcium silicate was not effective in its reduction.

RESUMO Uma das práticas desafi adoras de manejo é aumentar a produção de arroz utilizando menos água. O experimento foi realizado nas safras de

The objective of this work was to determine the duration of the effects of the mechanical interventions scarification and raised bed on soybean (Glycine max) grain yield on an Alfisol, as well as to evaluate, through physical indicators, if the use of cover plants during winter increases the duration of these effects. The experimental design was a complete randomized block with four replicates. Two factors were evaluated. The first consisted of types of soil preparation systems: SC14, scarification in November 2014; SC15, scarification in November 2015; RB14, raised bed built in November 2014; and RB15, raised bed built in November 2015. The second consisted of the type of cover crop used: winter fallow, oat, ryegrass, and wheat. From November 2015 to April 2016, soybean was cultivated under the different soil preparation systems. Soil density, total porosity, macroporosity, microporosity, soil saturated hydraulic conductivity, soil resistance to mechanical penetration, and soybean grain yield were evaluated. There was no effect of cover plants after one crop season on the maintenance of soil physical attributes. Changes in soil density, total porosity, and resistance to mechanical penetration, promoted by scarification, are noticeable up to at least 18 months. The continuance of these modifications reflects in soybean grain yield in the second harvest.

RESUMO O objetivo deste trabalho foi avaliar o efeito de diferentes manejos da cultura do azevém na entressafra do arroz irrigado, sobre o estabelecimento inicial de plantas, a ciclagem de nutrientes e o rendimento de grãos de arroz. O experimento Use of ryegrass in lowlands intensifies the nutrient cycling; however, it is recommended that in non grazed ryegrass the desiccation should be performed 60 days before the irrigated rice planting without reducing grain yield. Ryegrass hay production is a viable alternative for the off-season in lowlands because it does not reduce the initial establishment of irrigated rice plant.Key words: Oryza sativa, crops succession, cover crop, hay production. INTRODUÇÃOO sistema de semeadura direta em áreas de várzea pode ser incrementado através da implantação de plantas de cobertura de solo após a colheita do arroz irrigado (Oryza sativa). Essa prática pode incrementar a renda do produtor rural, através da utilização de uma cultura forrageira para produção de feno ou para pastejo. Além disso, esse sistema pode impactar positivamente na sustentabilidade do sistema de produção, em razão da ciclagem de nutrientes oriundos da palha remanescente do arroz irrigado pela cultura sucessora, o que possibilitaria otimizar o uso desses nutrientes e minimizar as suas perdas para o ambiente.Desse modo, quando se utilizam culturas em sucessão, busca-se, além da ciclagem de nutrientes, o sincronismo entre a liberação destes pela planta de cobertura e a absorção pela cultura sucessora. Nesse sentido, considera-se uma condição ideal

e use of pesticides assists in integrated programs that aim high yield and quality grains in irrigated rice (Oryza sativa L.). However, the use of pesticides can pose risk to rice quality as well as the environment and general population. erefore, the objective of this study was to investigate the dissipation and persistence of fungicides (azoxystrobin and difenoconazole) and the insecticides (lambda-cyhalothrin and thiamethoxam) in irrigation water, soil, rice plant, panicle, and rice grain. e study was conducted in the eld during the 2011/2012 crop season, with fungicides and insecticides applied to the aerial parts of the rice plants, the samples were collected in di erent moments during a 40-d monitoring period a er the application of the pesticides. Laboratory analyses to detect pesticide residues were determined by ultra-high performance liquid chromatography and by gas chromatography. Pesticide residues were detected in irrigation water and rice plants during the 40 d of monitoring. Azoxystrobin, difenoconazole, and thiamethoxan were transported into the environment due to over owed water from the rice eld, however pesticide residues were not detected in soil. Azoxystrobin, difenoconazole, thiamethoxan, and lambda-cyhalothrin residues were detected in rice hull, however, no residues were detected in neither brown nor polished rice grain.