frequência na região Centro-Oeste do Brasil e pode, sob condições de alta temperatura e alta umidade, causar sérios danos à cultura. O uso de cultivares resistentes ao patógeno é recomendado, porém são poucas as disponíveis no mercado. Este trabalho foi realizado visando avaliar a reação de doze cultivares comerciais de soja inoculados com C. cassiicola, em casa de vegetação e no campo. A severidade foi avaliada utilizando escala diagramática de severidade da mancha-alvo. As cultivares menos suscetíveis ao patógeno na casa de vegetação foram BRSGO 7960 e BRS Sambaíba e as mais suscetíveis foram BMX Potência RR e M-SOY 7908 RR. No campo, as cultivares menos suscetíveis foram M-SOY 8866, M-SOY 7908 RR e BMX Potência RR e as mais suscetíveis foram BRSGO 8360 e BRS Tracajá. Palavras-chave: Glycine max, mancha-alvo, resistência genética. ABSTRACT Reaction of soybean cultivars to Corynespora cassiicolaThe fungus Corynespora cassiicola, the causal agent of soybean target spot, frequently occurs in the Brazilian midwestern region. Under favorable climate conditions it can cause serious damage to this crop. The use of resistant cultivars is recommended although there are only a few available in the market. This investigation was carried out to evaluate the reaction of twelve soybean commercial cultivars to C. cassiicola. Severity was evaluated using a diagrammatic scale of target spot. The less susceptible cultivars in greenhouse were BRSGO 7960 and BRS Sambaíba and the most susceptible were BMX Potencia RR and M-SOY 7908 RR. In the field, the less susceptible cultivars were M-SOY 8866, M-SOY 7908 RR and BMX Potência RR and the most susceptible were BRSGO 8360 and BRS Tracajá.

O objetivo deste trabalho foi avaliar a seletividade de diferentes herbicidas à cultura do milho e a Brachiaria ruziziensis cultivadas no sistema de integração lavoura-pecuária. O experimento foi conduzido no Município de Nova Xavantina -MT, no período de janeiro a junho de 2008, em solo classificado como Latossolo Vermelho distrófico. O delineamento experimental utilizado foi o de blocos ao acaso, com quatro repetições, sendo avaliados 11 tratamentos: lactofen (96 g ha -1 ); lactofen (192 g ha -1 ); carfentrazone-ethyl (8 g ha -1 ); carfentrazone-ethyl (12 g ha -1 ); flumioxazin (25 g ha -1 ); flumioxazin (50 g ha -1 ); lactofen + flumioxazin (96 + 25 g ha -1 ); lactofen + flumioxazin (192 + 50 g ha -1 ); nicosulfuron (8 g ha -1 ); nicosulfuron (40 g ha -1 ) e testemunha sem herbicida. Os tratamentos foram aplicados aos 30 dias após a emergência da cultura do milho. Avaliaram-se os efeitos dos tratamentos sobre a altura de plantas, fitomassa seca e produtividade de grãos de milho e, também, sobre a fitomassa seca da B. ruziziensis. Os herbicidas flumioxazin, lactofen e carfentrazone-ethyl não apresentaram potencial para utilização em pós-emergência nesse sistema integrado de cultivo, principalmente por apresentar baixa seletividade à cultura do milho. O nicosulfuron na dose de 8 g ha -1 proporcionou produtividade de grãos de milho equivalente à testemunha sem herbicida, e pequena supressão inicial das plantas de B. ruziziensis, sendo, consequentemente, o mais indicado para o controle de plantas daninhas nesse sistema de integração lavoura-pecuária.

Ruzigrass (Urochola ruziziensis) has a large capacity to take up K from the soil, including non-exchangeable forms, and can play an important role in nutrient cycling in integrated production systems. However, K transport to roots of brachiarias is not well known, nor the nutrient dynamics in the rhizosphere, where a concentration gradient may be established towards the non-rhizospheric soil, creating a favorable environment for the release of non-exchangeable K. This study aimed to evaluate the effect of ruzigrass on K dynamics in the rhizosphere and on non-exchangeable K release. Ruzigrass was grown in pots filled with a Latossolo Vermelho Amarelo (Typic Hapludox) that was collected at 0.00-0.20 and 0.20-0.60 m layer from a cultivated area and fertilized with 0, 30, and 60 mg kg -1 of K, plus a treatment with forest soil, used as control. Thirty days after plant emergence, soil samples were taken at the following distances from the roots: 0.5, 1.0, 1.5, 3.0, 5.0, and 10.0 mm. For the highest exchangeable K rate (60 mg dm -3 ), the exchangeable K level was higher from 0 to 0.5 mm of the roots for both soils (0.00-0.20 and 0.20-0.60 m). Therefore, more K was transported to the rhizosphere than the plant could take up. A depletion of exchangeable K observed in the rhizosphere resulted in the release of K from non-exchangeable forms, as observed in the soils from 0.00-0.20 (60 mg dm -3 ) and 0.20-0.60 m (without application of K). Ruzigrass grown on low K soils without fertilizer application results in a larger exchangeable K depletion zone than in soils that were fertilized or originally high in exchangeable K, showing a high potential for K cycling in the system.

Liming and N fertilization are common practices for optimizing crop yields in tropical agriculture, but the adequate N rate to ensure crop development, enhance yields and N use efficiency, and improve soil chemical properties has not been established for grass rotation. We assessed the optimal N fertilizer rate for combination with liming in an agricultural system composed of two grasses (maize and rice) in rotation under no-till (NT) conditions. Four N rates (0, 50, 100, and 150 kg N·ha−1) were tested under two liming conditions. Maize (11 Mg·ha−1) and rice (5 Mg·ha−1) yields were highest with lime and 150 kg N·ha−1 applications. At 18 months after liming, lime application increased soil pH. In addition, combining liming with N fertilization further increased SOM content at all N rates. Lime increased available P, exchangeable Ca2+ and Mg2+, and BS at N rates of 0, 50, and 100 kg N·ha−1. Overall, combining liming and N fertilization is beneficial for grass crops under NT conditions, as evidenced by enhanced maize and rice N use efficiency and yields. N fertilization rates of 100 and 150 kg N·ha−1 under lime amendment provided the best improvements in crop yields in this cropping system.

Slow-release fertilizers have been proposed as tools to increase P fertilizer use efficiency in tropical acidic soils with high P adsorption, low P availability, and mobility. However, results have been controversial since soil diversity and the fertilizer itself may influence the results, which is not completely understood. Soil P diffusion and availability were studied in soils with different P fertilization histories, where triple superphosphate (TSP) and single superphosphate (SSP) coated with a polymer or with humic acid and complexed with humic acid were applied under laboratory conditions. No difference in soil P availability and diffusion was observed between humic acid-complexed, polymer, and humic acid-coated TSP and conventional TSP. For SSP, soil P availability was 15 to 30% lower in the region of application for the polymer and 0 to 16% for the humic-coated fertilizer. For the polymer-coated SSP, P diffusion was lower in some soils. With both base fertilizers, the soil adsorption capacity was more determinant of P diffusion than the protection of the fertilizers. Coating P fertilizers with polymer and complexing or coating the fertilizer with humic acid does not increase P availability or diffusivity in soil since these processes are driven mainly by the soil characteristics. Therefore, the potential of these controlled-release P fertilizers in increasing P use efficiency is low.