summarY the expansion of Brazilian agriculture has led to a heavy dependence on imported fertilizers to ensure the supply of the growing food demand. this fact has contributed to a growing interest in alternative nutrient sources, such as ground silicate rocks. it is necessary, however, to know the potential of nutrient release and changes these materials can cause in soils. the purpose of this study was to characterize six silicate rocks and evaluate their effects on the chemical properties of treated soil, assessed by chemical extractants after greenhouse incubation. the experimental design consisted of completely randomized plots, in a 3 x 6 factorial scheme, with four replications. the factors were potassium levels (0-control: without silicate rock application; 200; 400; 600 kg ha -1 of k 2 o), supplied as six silicate rock types (breccia, biotite schist, ultramafic rock, phlogopite schist and two types of mining waste). the chemical, physical and mineralogical properties of the alternative rock fertilizers were characterized. treatments were applied to a dystrophic red-Yellow oxisol (ferralsol), which was incubated for 100 days, at 70 % (w/w) moisture in 3.7 kg/pots. the soil was evaluated for ph; calcium and magnesium were extracted with kCl 1 mol l -1 ; potassium, phosphorus and sodium by mehlich 1; nickel, copper and zinc with dtPa; and the saturation of the cation exchange capacity was calculated for aluminum, calcium, magnesium, potassium, and sodium, and overall base saturation. the alternative fertilizers affected soil chemical properties. ultramafic rock and Chapada mining byproduct (CmB) were the silicate rocks that most influenced (1) received for publication in June 29, 2011 and approved in april 12, 2012. (2) Professor soil science department, federal university of lavras -ufla. CP 3037, CeP 37200-000 lavras (mG), Brazil. e-mails:douglasguelfi@dcs.ufla.br; guilherm@dcs.ufla.br (3) research embrapa Cerrados, rodovia Br 020, km 18, CeP 73370-970 Planaltina (df), Brazil. e-mails: giuliano.marchi@cpac. embrapa.br; rein@cpac.embrapa.br (4) Professor faculty of agronomy and Veterinary medicine, university of Brasília, Campus universitário darcy ribeiro, asa norte, CeP 70910-970 Brasília (df), Brazil. e-mail: spehar@unb.br (5) student of the doctorate Program on

The current high price of potassium chloride and the dependence of Brazil on imported materials to supply the domestic demand call for studies evaluating the efficiency of alternative sources of nutrients. The aim of this work was to evaluate the effect of silicate rock powder and a manganese mining by-product, and secondary materials originated from these two materials, on soil chemical properties and on brachiaria production. This greenhouse experiment was conducted in pots with 5 kg of soil (Latossolo Vermelho-Amarelo distrófico -Oxisol). The alternative nutrient sources were: verdete, verdete treated with NH 4 OH, phonolite, ultramafic rock, mining waste and the proportion of 75 % of these K fertilizers and 25 % lime. Mixtures containing 25 % of lime were heated at 800 ºC for 1 h. These sources were applied at rates of 0, 150, 300, 450 and 600 kg ha -1 K 2 O, and incubated for 45 days. The mixtures of heated silicate rocks with lime promoted higher increases in soil pH in decreasing order: ultramafic rock>verdete>phonolite>mining waste. Applying the mining waste-lime mixture increased soil exchangeable K, and available P when ultramafic rock was incorporated. When ultramafic rock was applied, the release of Ca 2+ increased significantly. Mining subproduct released the highest amount of Zn 2+ and mn 2+ to the soil. The application of alternative sources of K, with variable chemical composition, altered the nutrient availability and soil chemical properties, improving mainly plant development and K plant uptake, and are important nutrient sources.

We investigated the effects of chromate (CrVI) and sulfate on their uptake and translocation in As-hyperaccumulator Pteris vittata. Plants were exposed to 1) 0.1 mM CrVI and 0, 0.25, 1.25 or 2.5 mM sulfate or 2) 0.25 mM sulfate and 0, 0.5, 2.5 or 5.0 mM CrVI for 1 d in hydroponics. P. vittata accumulated 26 and 1261 mg kg(-1) Cr in the fronds and roots at CrVI0.1, and 2197 and 1589 mg kg(-1) S in the fronds and roots at S0.25. Increasing sulfate concentrations increased Cr root concentrations by 16-66% and helped CrVI reduction to CrIII whereas increasing CrVI concentrations increased frond sulfate concentrations by 3-27%. Increasing sulfate concentrations enhanced TBARS concentrations in the biomass, indicating oxidative stress caused lipid peroxidation in plant cell membranes. However, addition of 0.25-2.5 mM sulfate alleviated CrVI's toxic effects and decreased TBARS from 23.5 to 9.46-12.3 μmol g(-1) FW. Though CrVI was supplied, 78-96% of CrIII was in the biomass, indicating efficient CrVI reduction to CrIII by P. vittata. The data indicated the amazing ability of P. vittata in Cr uptake at 289 mg kg(-1) h(-1) with little translocation to the fronds. These results indicated that P. vittata had potential in Cr phytoremediation in contaminated sites but further studies are needed to evaluate this potential. The facts that CrVI and sulfate helped each other in uptake by P. vittata suggest that CrVI was not competing with sulfate uptake in P. vittata. However, the mechanisms of how sulfate and CrVI enhance each other's accumulation in P. vittata need further investigation.

RESUMO -Considerando a possibilidade de atrasar o crescimento inicial de gramíneas forrageiras por meio de semeaduras em maior profundidade, de forma a proporcionar vantagem competitiva à cultura de grãos em sistemas consorciados, foram avaliados a emergência e o crescimento de cultivares de Urochloa spp. em diferentes profundidades de semeadura. O experimento foi conduzido em casa de vegetação com U. brizantha cv. Marandu e cv. Piatã e U. decumbens cv. Basilisk, semeadas nas profundidades de 0, 3, 6, 9 e 12 cm. Observou-se comportamento semelhante entre os cultivares de U. brizantha quanto à porcentagem e velocidade de emergência, à altura e à massa de matéria seca de plantas aos 28 dias após a semeadura (DAS); entretanto, esses resultados diferiram dos de U. decumbens, à exceção da altura de U. brizantha cv. Piatã. As variáveis avaliadas, para todos os cultivares, tenderam à redução em profundidades maiores que 6 cm. O atraso na emergência a 0 cm, para todos os cultivares de Urochloa, não resultou em redução na altura e massa de matéria seca das plantas.Palavras-chave: Brachiaria brizantha, Brachiaria decumbens, braquiarão, capim-braquiária, capim-piatã.ABSTRACT -The emergence and growth of Urochloa spp. at different sowing depths was evaluated, considering the possibility of delaying the initial growth of forage grass by sowing it deeper to provide competitive advantage to the grain culture in crop-pasture association systems. The experiment was conducted in a greenhouse with U. brizantha cv. Marandu and cv. Piatã and U. decumbens cv. Basilisk, and sowing depths of 0, 3, 6, 9, and 12 cm. Similar behavior between U. brizantha cultivars was observed for daily emerged seedlings, emergence percentage, height and dry matter of plants at 28 days after sowing (DAS); however, these results differed from those obtained for U. decumbens, except for the height of U. brizantha cv. Piatã. The evaluated variables, for all cultivars, tended to be reduced when sown deeper than 6 cm. The delay in emergence at 0 cm without reduction, for all cultivars of Urochloa, did not result in reduced height and dry matter weight.

SUMMARYKinetic studies on soil potassium release can contribute to a better understanding of K availability to plants. This study was conducted to evaluate K release rates from the whole soil, clay, silt, and sand fractions of B-horizon samples of a basalt-derived Oxisol and a sienite-derived Ultisol, both representative soils from coffee regions of Minas Gerais State, Brazil. Potassium was extracted from each fraction after eight different shaking time periods (0-665 h) with either 0.001 mol L -1 citrate or oxalate at a 1:10 solid:solution ratio. First-order, Elovich, zero-order, and parabolic diffusion equations were used to parameterize the time dependence of K release. For the Oxisol, the first-order equation fitted best to the experimental data of K release, with similar rates for all fractions and independent of the presence of citrate or oxalate in the extractant solution. For all studied Ultisol fractions, in which K release rates increased when extractions were performed with citrate solution, the Elovich model described K release kinetics most adequately. The highest potassium release rate of the Ultisol silt fraction was probably due to the transference of "non-exchangeable" K to the extractant solution, whereas in the Oxisol exchangeable potassium represented the main K source in all studied fractions. Index terms: successive extractions, first order, zero order, parabolic diffusion, Elovich.( RESUMO: CINÉTICA DE LIBERAÇÃO DO POTÁSSIO EM SOLOS DE REGIÕES CAFEEIRAS: EFEITO DE ÁCIDOS ORGÂNICOSEstudos de cinética de liberação de K podem contribuir para avaliação da disponibilidade deste nutriente no solo para as plantas. Este trabalho teve como objetivos investigar a cinética de liberação do potássio nas frações terra fina, areia, silte e argila de dois solos do Estado de Minas Gerais, Brasil, originalmente cultivados com cafeeiro e comparar quatro equações para descrevê-la. As frações foram submetidas a oito extrações sucessivas (0 a 665 h) com citrato e oxalato 1 mmol L -1 , sendo os resultados de K liberado somados e plotados em função do tempo. Foram comparadas as equações de ordem zero, primeira ordem, Elovich e parabólica de difusão, a fim de verificar qual delas melhor descreve a cinética. Na condução do experimento utilizaram-se amostras do horizonte B de um Latossolo Vermelho distroférrico originado de basalto e de um Nitossolo originado de sienito nefelínico. Para cada equação foram calculados o coeficiente de correlação (r) e o erro-padrão da estimativa (EP). A equação de primeira ordem descreveu melhor os resultados do Latossolo e a equação de Elovich se ajustou melhor aos resultados do Nitossolo. As velocidades de liberação do K para o Latossolo foram semelhantes em todas as frações estudadas, não sendo observado efeito dos ácidos orgânicos na velocidade de liberação do K, porque a maior parte do K liberado foi proveniente da forma trocável. No Nitossolo, o citrato acelerou a liberação do K em todas as frações estudadas, e a fração silte foi a que apresentou maior velocidade, pois possivel...

-Hybrids of Sorghum sudanensis (sudangrass) and Sorghum bicolor genotypes can produce high amounts of biomass, sorgoleone (a long chain hydroquinone), and other phytotoxic substances. Shoots and roots of a sorghum-sudangrass hybrid (cv. Trudan 8) were collected 10, 20, 30, 40, and 50 days after emergence. Four concentrations of aqueous extracts from the shoots and roots (0, 0.4, 2, and 10 g L -1 , w/v) were used to treat seeds of lettuce (Lactuca sativa), tomato (Lycopersicum sculentum), purslane (Portulaca oleracea), and pigweed (Amaranthus retroflexus). Seed germination of lettuce, tomato, and pigweed was inhibited by extracts from sorghum-sudangrass shoots at 10 g L -1 when made from sorghum-sudangrass plants 20 days or less in age. Seed germination of purslane was not inhibited by any sorghum-sudangrass extract. Growth of the four species evaluated were systematically inhibited when treated with 10 g L -1 extracts from sorghum-sudangrass shoots harvested up to 10 days after emergence.Keywords: allelopathy, germination inhibition, lettuce (Lactuca sativa), tomato (Lycopersicum sculentum), pigweed (Amaranthus retroflexus) and purslane (Portulaca oleracea).RESUMO -Os capins híbridos obtidos pelo cruzamento entre Sorghum sudanensis (capimsudão) e genótipos de Sorghum bicolor possuem alto potencial para produção de biomassa e para controle de plantas daninhas pela produção de substâncias fitotóxicas, como o sorgoleone (uma hidroquinona de cadeia longa). Sementes de alface (Lactuca sativa), tomate (Lycopersicum sculentum), beldroega (Portulaca oleracea) e caruru (Amaranthus retroflexus) foram submetidas a tratamentos com extratos aquosos da parte aérea e das raízes do híbrido de sorgo com capim-sudão, cv. Trudan 8, colhido em cinco diferentes estádios de crescimento (10, 20, 30, 40 e 50 dias após a emergência). Os extratos foram preparados em quatro concentrações (0, 0,4, 2 e 10 g L -1, p/v) e aplicados em quatro repetições. Após os tratamentos, a germinação e o comprimento de plântulas das espécies foram avaliados. A germinação de sementes de tomate, caruru e alface foi inibida pelos extratos da parte aérea das plantas de Trudan 8, na concentração de 10 g L 1 , colhidas até os 20 dias após a emergência. A germinação de sementes de beldroega, no tocante à porcentagem de germinação, não foi inibida pelos extratos de Trudan 8. O crescimento das quatro espécies avaliadas foi inibido quando tratadas com extratos aquosos da parte aérea de Trudan 8, colhida até os 10 dias após a emergência, na concentração de 10 g L -1. Palavras-chave: alelopatia, inibidor de germinação, alface (Lactuca sativa), tomate (Lycopersicum sculentum), caruru (Amaranthus retroflexus) e beldroega (Portulaca oleracea).

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INTRODUÇÃOAtualmente, a adubação potássica de solos agrícolas brasileiros é realizada empregando-se sais solúveis em água, principalmente o cloreto de potássio (KCl). Em virtude da pequena produção brasileira (7,60 % do consumo aparente), quando comparada à grande demanda interna pelo produto, o Brasil situa-se no contexto mundial como grande importador de fertilizante potássico, principalmente de países como o Canadá (31,18 %), Bielorrússia (21,96 %), Alemanha (18,93 %), Israel (10,73 %) e Rússia (9,24 %). Essa situação é agravada pela única Potassium solubilization in verdete and limestone mixtures treated thermochemically Brazil owns reserves of low solubility potassium silicate rocks, being necessary the development of alternative processing methods to increase their solubility, so they can be efficiently used in agriculture. This study aimed to get new technological routes to produce alternative potassium sources from verdete. Calcination and alkaline solubilization tests were performed for verdete and limestone mixtures. The calcination process followed by cooling at room temperature provided a higher potassium availability than other methods used. However, the increase of limestone content, concerning verdete, decreased the potassium solubility. The treatment limestone:verdete, in the proportion of 0:100, after calcination at 800 ºC during one hour and then treated with NH 4 OH, and in the proportion of 25:75, after calcination, release proportionally higher amounts of K than non-calcinated samples. ABSTRACT RESUMOKEY-WORDS: Calcination; alkaline solubilization; alternative source of potassium.