Doses e fontes de nitrogênio na recuperação das características estruturais e produtivas do capim-marandu 1Rates and sources of nitrogen in the recovery of the structural and productive characteristics of marandu grass ABSTRACT -To replenish soil fertility is one of the ways of recovering the productive capacity of degraded pasture. Nitrogen fertilisation is fundamental to increasing forage production, especially when it comes to the recovery of pasture. With this in mind, the objective of this work was to evaluate the structural characteristics and dry matter (DM) accumulation of the leaf blades and sheathed stems of marandu-grass pasture at a moderate stage of degradation, for different dosages and sources of nitrogen, during a three-year period. The experiment was carried out from July, 2003 to March, 2006 at the Model Farm of the Goiás State University (UEG), over an area of 882 m 2 with plots of 20 m 2 and usable area of 6 m 2 . The experimental design was of randomized blocks with three replications. The treatments in the plots were characterized by a 2 x 4 factorial, being two nitrogen sources (ammonium sulphate and urea) and four nitrogen dosages (0; 100; 200 and 300 kg ha -1 yr -1). For each sub-plot, treatments were represented by the years (2004, 2005 and 2006), as relating to the time of the recovery of the pasture. Nitrogen fertilization was divided into three applications, following each harvesting of the grass for forage evaluation. The results showed that nitrogen fertilisation influenced the structural characteristics and dry matter accumulation of marandu grass, and hence its recovery. The dosage of 300 kg ha -1 yr -1 of ammonium sulphate resulted in greater values for plant height, tiller density and leaf-blade dry matter.

High nitrogen losses by ammonia volatilization are expected when urea is used as the source of N. The use of controlled-release urea and urease inhibitors are possible strategies to reduce such losses and increase nitrogen use efficiency. This study aimed to evaluate nitrogen losses by ammonia volatilization from stabilized, slow and controlled release urea and its absorption by maize grown under no-till in an improved Cerrado soil. Four N sources were used: conventional urea, urea + N-(n-butyl) thiophosphoric triamide (NBPT), urea + Cu and B and urea coated by sulfur + polymers. These N sources were surface applied along the rows using three N doses of 100, 150 and 200 kg ha -1 . No N was added to the control. Data were collected regarding N losses by volatilization, the N contents accumulated in the stubble and grains, and the yields of the stubble and grains. Stabilized urea and slow release urea were efficient for postponing the ammonia volatilization peaks. The urease inhibitors postponed the peaks for up to two days, reducing the accumulated volatilization by 18% when compared with common urea. Polymer sulfur coated urea resulted in a 37% reduction in ammonia volatilization. Increasing the N application rate to 200 kg ha -1 resulted in 16% greater yields and 37% greater N accumulation in the plants relative to the control. However, the stabilized and slow-release urea did not improve the N accumulation or yield. Consequently, the nitrogen use efficiency of maize was not improved relative to the use of conventional urea.Index terms: Nitrogen fertilizers; NH 3 -N losses; polymer sulfur coated urea; urease inhibitors; Zea mays L. RESUMOA aplicação de ureia, frequentemente, gera grandes perdas de N por volatilização e o uso de revestimentos e inibidores de urease, podem reduzir essas perdas. Neste estudo, objetivou-se avaliar as perdas de nitrogênio pela ureia estabilizada e de liberação lenta ou controlada e sua absorção pelo milho cultivado em plantio direto, em solo de Cerrado, com fertilidade construída. Quatro fontes de N foram utilizadas: ureia convencional, ureia + N-(n-butyl)thiophosphoric triamide (NBPT), ureia + Cu + B e ureia revestida por enxofre e polímeros. Essas fontes de N foram aplicadas em superfície nas doses de 100, 150 e 200 kg ha -1 . Não houve aplicação de N no controle. Avaliaram-se as perdas de N por volatilização, o acúmulo de N nos grãos e palhada e produção de grãos e de palhada. A ureia estabilizada e de liberação controlada foi eficiente em atrasar os picos de volatilização de amônia. Os inibidores de urease atrasaram os picos de volatilização em até dois dias, reduzindo a volatilização acumulada em até 18%, quando comparado à ureia comum. A ureia revestida por enxofre e polímeros resultou em uma redução de 37% na volatilização de amônia. O aumento da dose de N até 200 kg ha -1 resultou em aumento de 16% na produtividade e 37% no acúmulo de N em relação ao controle. Entretanto, a ureia estabilizada e de liberação controlada não aumentou o acúmulo de N ou a produtividade...

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.

RESUMOA mangabeira destaca-se por possuir um grande potencial como planta frutífera. Suas sementes apresentam recalcitrância, dificultando sua propagação, o que torna evidente a necessidade da obtenção de mudas por via assexuada. Neste contexto, a cultura de tecidos apresenta-se como uma alternativa a ser utilizada. Entre os fatores que afetam a morfogênese in vitro, as citocininas merecem destaque, pois influenciam na diferenciação de gemas e no crescimento das brotações. Assim sendo, avaliou-se, neste trabalho, a influência de três diferentes fontes de citocinina (6-benzilaminopurina -BAP, cinetina -CIN e thidiazuron -TDZ) na indução de brotações in vitro de mangabeira, bem como o efeito residual dessa classe de reguladores no enraizamento e na multiplicação em subcultivos sucessivos. Os resultados mostraram que, entre as citocininas testadas, a 6-benzilaminopurina foi a que induziu maior número de brotações (1,98), gemas (19,22) e folhas (18,86) por explante, tendo promovido a formação de brotos de maior comprimento (4,55 cm). As brotações oriundas de meio WPM basal apresentaram maior facilidade de enraizamento. A 6-benzilaminopurina foi responsável pela maior taxa de multiplicação (9,61) de brotações de mangabeira. Os subcultivos sucessivos diminuíram a capacidade de multiplicação de explantes caulinares da espécie.Termos para indexação: Micropropagação, mangabeira, subcultivos. ABSTRACTThe mangabeira stands out for having a strong potential for fruit production. Its seeds present recalcitrance, making its propagation difficult, which makes much clear the need to obtain seedlings through asexual methods. In this context, the tissue culture presents as an alternative to be used. Among the factors that affect in vitro morphogenesis, the cytokinins should be highlighted as it influences the differentiation of buds and shoot growth. In this context the influence of three different sources of cytokinins (6-benzylaminopurine -BAP, kinetin -CIN and thidiazuron -TDZ) was evaluated on the induction of in vitro mangabeira shoots, as well as the residual effect of this type of regulator on rooting and multiplication in successive subcultures. The results showed that among the tested cytokinins, the 6-benzylaminopurine was the one that induced a higher number of shoots (1.98), buds (19.22) and leaves (18.86) per explant, promoting the formation of shoots with higher length (4.55 cm). The shoots from basal WPM medium rooted easier. The 6-benzylaminopurine was responsible for the highest rate of multiplication (9.61) of mangabeira shoots. Sucessive subcultures decreased the capacity of shoot multiplication.