Nitrogen losses from the soil-plant system may be influenced by herbicide applications. In order to evaluate N loss in brachiaria (Brachiaria decumbens) after application of the herbicides glyphosate and glufosinate-ammonium, an experiment was carried out in a greenhouse as a completely randomized design, with three treatments and six replicates. Treatments were as follows: i) desiccation of brachiaria-plants with glyphosate; ii) desiccation of brachiaria-plants with glufosinate-ammonium; and iii) control, without herbicide application. The plants were cultivated in 4 kg pots of sandy soil and fertilized with ammonium sulfate-15 N, (200 mg kg ) in order to quantify the allocation of the fertilizer-N and its recovery in the soil-plant system. Plants treated with the herbicides had less N accumulation and less recovery of the fertilizer-N ( 15 N) relative to the control. In the soil, the greatest recovery of 15 N-fertilizer occurred for treatments where N was applied, possibly due to the occurrence of other N compound losses to the soil, like root exudation and root death. The total recovery of 15 N-fertilizer in the soil-plant system was higher in the control than in the treated plants showing the direct action of the herbicides on nitrogen loss, and especially by the above-ground part of the brachiaria plants. Key words: 15 N, ammonium exchange, Gramineae, herbicides PERDAS DE NITROGÊNIO POR Brachiaria decumbens APÓS A APLICAÇÃO DE GLIFOSATO OU GLUFOSINATO DE AMÔNIORESUMO: As perdas de nitrogênio no sistema solo-planta podem ser influenciadas pela aplicação de herbicidas. Com o objetivo de avaliar a perda de N do capim-Brachiaria (Brachiaria decumbens) após a aplicação dos herbicidas glifosato e glufosinato de amônio, foi realizado um experimento em casade-vegetação em delineamento inteiramente aleatorizado (DIA), com três tratamentos e seis repetições. Os tratamentos foram os seguintes: i) dessecação de plantas de braquiária com o herbicida glifosato; ii) dessecação de plantas de braquiária com herbicida glufosinato de amônio e iii) testemunha, sem aplicação de herbicida. As plantas foram cultivadas em vasos com 4 kg de solo arenoso e foram fertilizadas com sulfato de amônio ( 15 N), na dose de 200 mg kg -1 , com o intuito de quantificar a alocação de N-fertilizante ( 15 N) e sua recuperação no sistema solo-planta. As plantas tratadas com os herbicidas apresentaram menor acúmulo de N e menor recuperação do N-fertilizante ( 15 N) em relação à testemunha. No solo a maior recuperação do 15 N-fertilizante ocorreu nos tratamentos em que foram aplicados os herbicidas, possivelmente, devido à ocorrência de perda de compostos nitrogenados para o solo por exsudação radicular e morte de raízes. A recuperação total do 15 N-fertilizante no sistema solo-planta foi maior na testemunha que nos tratamentos, evidenciando-se a ação direta dos herbicidas nas perdas de nitrogênio, especialmente, pela parte aérea do capim-Brachiaria. Palavras-chave: 15 N, perdas de nitrogênio, braquiária, herbicidas

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The forthcoming of silicon (Si) highly soluble sources provided a suitable alternative to Si use in agroecosystems. There are many benefits associated to Si application in crops, such as improvement in feed quality. In this sense, the aim of this work was to evaluate the effect of Si foliar application on physiological quality, biomass production, and silicon accumulation in Sorghum bicolor. The experiment was conducted under greenhouse condition using an entirely randomized design, with five Si rates (0 as control), 0.84, 1.68, 2.52, and 3.36g L -1 of Si) applied as potassium and sodium silicate, with four repetitions. In each treatment, applied solutions were balanced in potassium in order to isolate the Si effect. The following measurements were taken: growth, biomass production, Si accumulation, and physiological quality. Supplying Si via leaves did not affect the sorghum growth rate and the relative chlorophyll index; however, leaf area increased 23% with the use of 2.36 g L -1 of Si. Physiological variables are influenced by increasing Si rates, with rates close to 1.68 g L -1 of Si causing the best photosynthetic rates and stomatal conductance. The use of potassium silicate as a source of silicon is an alternative for productivity increases up to 30%, but an economic study on the viability of its commercial application in the production chain of Sorghum bicolor is necessary.

RESUMONos últimos anos, tem-se procurado elevar os teores de C orgânico do solo e, ao mesmo tempo, aumentar a produtividade das culturas. Neste contexto, o sistema semeadura direta (SSD) tem importante participação, principalmente na região dos Cerrados. Entretanto, para se alcançar altas produtividades, as gramíneas requerem a adição de doses elevadas de adubos nitrogenados. Este trabalho teve por objetivo avaliar as alterações no solo decorrentes da aplicação de palha e de N em solo cultivado com milho por 10 anos (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) em SSD. O experimento foi desenvolvido na Embrapa-Milho e Sorgo, em Sete Lagoas-MG, em um Latossolo Vermelho distrófico típico sob cerrado. Os tratamentos constaram da combinação de palha sobre o solo (0, 3, 6, 9 e 12Mg ha -1 de matéria seca) dispostas nas parcelas, e de cinco níveis de N aplicados em cobertura (0, 40, 80, 120 e 160kg ha -1 ), na forma de uréia, dispostos nas subparcelas. Foram realizadas duas coletas de solo (antes e após uma calagem), nas profundidades de 0-0,025; 0, 025-0,05; 0,05-0,10; 0,10-0,20; 0,20-0,40m. Análises químicas e físicas de rotina foram efetuadas usando-se métodos padrões. Os teores de C orgânico e de K foram influenciados pelas doses de palha e aumentaram à medida que se aumentou a aplicação de palha sobre o solo. A variação nas doses de N promoveu alterações no pH, nos teores de Ca, Mg e nas saturações por bases e por Al até a profundidade de 0,20m. A calagem superficial promoveu o aumento do pH do solo em profundidade e dos teores de Ca, até 0,20m, provavelmente devido à alta pluviosidade no período pós-calagem (1600mm em oito meses). Palavras-chave: calagem superficial; adubação nitrogenada;Latossolo; Cerrados. ABSTRACTAgricultural practices have been trying to increase the content of organic C in soils and at the same time to increase yields. In this context, the no-till system (NTS) has an important role to play, particularly in the Cerrado region of Brazil. However, to reach high yields, the crops demand high inputs of N fertilizers. The objective of this work was to evaluate the modifications induced in the soil after ten years (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) of NTS, influenced by different straw and N doses. The experiment was set at the Embrapa farm in Sete Lagoas-MG, on a typic Dystrofic Red Latosol under Cerrado vegetation. The treatments consisted of five straw doses (0, 3, 6, 9 e 12Mg ha -1 of dry matter) in the plot and five doses of N (0, 40, 80, 120 e 160kg ha -1 ) as urea in the subplot. Two samplings were accomplished, before and after liming. The soil layers sampled were 0-0.025; 0.025-0.05; 0.05-0.10; 0.10-0.20; and 0.20-0.40m. Routine soil physical and chemical variables were measured according to standard procedures. The contents of organic C and K were influenced by the different straw doses and increased as the application of straw increased. The different doses of N influenced pH, Ca, Mg, Al, base and Al saturation, up to 0.20m. The surfac...

Resumo -Este trabalho foi desenvolvido com o objetivo de avaliar a efi cácia do herbicida glifosato, para a dessecação de trapoeraba (Commelina benghalensis) e outras plantas daninhas, quando combinado a diferentes concentrações de sulfato de amônio ou uréia. Foram conduzidos três experimentos com tratamentos semelhantes: dois em campo e um em casa de vegetação. Os tratamentos aplicados em campo foram: glifosato (360 g ha -1 de e.a.), isolado ou acrescido de quatro concentrações de sulfato de amônio (2,5, 5, 10 e 20 g L -1 ) ou uréia (1,5, 3, 6 e 12 g L -1 ); glifosato a 720 g ha -1 de e.a., aplicado isoladamente; e testemunha sem aplicação. Em casa de vegetação, para o controle específi co da trapoeraba, as doses de glifosato foram elevadas para 720 (isolado e nas combinações) e 1.440 g ha -1 de e.a. A adição de sulfato de amônio à calda do glifosato elevou o controle das plantas daninhas em campo, para as concentrações com até 10 g L -1 . O herbicida glifosato não foi efi caz no controle da trapoeraba, em nenhumas das doses usadas. A adição de uréia não promoveu incrementos de controle em condição de campo; porém, para concentrações de até 6 g L -1 , melhorou o controle da trapoeraba, na avaliação conduzida aos 28 dias após aplicação.Termos para indexação: Commelina benghalensis, controle químico, efi cácia, herbicida. Glyphosate applied with different concentrations of urea or ammonium sulfate for weed desiccationAbstract -This work was developed with the objective of evaluating glyphosate effi cacy for Bengal dayfl ower (Commelina benghalensis) and other weeds desiccation, when combined to different concentrations of ammonium sulfate or urea. Three experiments were carried out with similar treatments: two in fi eld conditions and one in greenhouse. Treatments applied in fi eld conditions were: glyphosate at 360 g ha -1 a.e., isolated or combined to four concentrations of ammonium sulfate (2.5, 5, 10, and 20 g L -1 ) or urea (1.5, 3, 6, and 12 g L -1 ); glyphosate at 720 g ha -1 a.e., applied isolately; and checks without application. In greenhouse, for the specifi c control on Bengal dayfl ower, glyphosate rates were increased to 720 (isolated or in combination) and to 1,440 g ha -1 a.e. Ammonium sulfate addition to glyphosate spray solution increased fi eld weed control, when concentrations up to 10 g L -1 were used. None of the glyphosate rates were effi cient to control Bengal dayfl ower. Urea addition to spray solution did not improve weed control in fi eld conditions; however, it increased Bengal dayfl ower control for concentrations up to 6 g L -1 , at the evaluation after 28 days of application.

The objective of this study is to evaluate the effects of sources and doses of boron on the physiological quality and production yield of Phaseolus vulgaris grown using a central pivot irrigated system on a tropical climate region. The experiment was a 4x5 factorial design representing four sources of boron (boric acid, borax, borogran and FTE BR 12) and five boron doses (0, 1, 2, 3 and 4 kg ha -1 ), with four replications. The following parameters were measured: relative chlorophyll index, transpiration, CO 2 internal concentration, stomatal conductance, net photosynthesis, B content, grain yield and economic analysis. The relative chlorophyll index (RCI) of plants showed no significant effects at both 28 and 46 days after emergence (DAE). The extraction order of boron was boric acid > borax > FTE BR12 > Borogran. The application of boron did not affect the physiological quality (stomatal conductance, transpiration and internal concentration of CO 2 ). However, the net photosynthetic rate was lower when boric acid was applied in relation to other sources. The maximum production (4,446 kg ha -1 ) was obtained using 1.35 kg ha -1 of B with the use of boric acid. However, according to an evaluation of economic viability, it is observed that there are economic differences among sources of boron and evaluated doses. The application of 4 kg ha -1 of borax provides the highest economic return.

Current research shows that glyphosate herbicides can increase nitrogen exudation by plant roots and, as a consequence, favor pathogenic fungal colonization in soil. In Brazilian agroecosystems, the main herbicides used in conservationist systems for glyphosate substitution are glufosinate and paraquat. However, no studies have been developed that to evaluate the effects of these herbicides on nitrogen exudation by roots. This work was carried out with the objective of evaluating the exudation of nitrogen ( 15 N) compounds and root detachment after the application of glyphosate, glufosinate-ammonium or paraquat on Brachiaria decumbens Stapf. The ammonium concentration in the plant's tissues and the nitrogen ( 15 N) recovery in the plant-solution system were also evaluated. The nitrogen left by the soil-solution system and the ammonium concentration in the plant's tissues were increased after glyphosate or glufosinate application, but they were not modified by paraquat. Nitrogen compound exudation and root detachment were increased by the desiccation of Brachiaria decumbens Stapf by the use of the following herbicides: glyphosate, glufosinateammonium and paraquat. This increase demonstrated that the nitrogen exudation was not affected by a particular herbicide's mode of action.

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