In Brazilian agriculture, urea is the most commonly used nitrogen (N) source, in spite of having the disadvantage of losing considerable amounts of N by ammonia-N volatilization. The objectives of this study were to evaluate: N lossby ammonia volatilization from: [urea coated with copper sulfate and boric acid], [urea coated with zeolite], [urea+ammonium sulfate], [urea coated with copper sulfate and boric acid+ammonium sulfate], [common urea] and [ammonium nitrate]; and the effect of these N source son the maize yield in terms of amount and quality. The treatments were applied to the surface of a soil under no-tillage maize, in two growing seasons. The first season (2009/2010) was after a maize crop (maize straw left on the soil surface) and the second cycle (2012/2011) after a soybean crop. Due to the weather conditions during the experiments, the volatilization of ammonia-N was highest in the first four days after application of the N sources. Of all urea sources, under volatilization-favorable conditions, the loss of ammonia from urea coated with copper sulfate and boric acid was lowest, while under high rainfall, the losses from the different urea sources was similar, i.e., an adequate rainfall was favorablet o reduce volatilization. The ammonia volatilization losses were greatest in the first four days after application. Maize grain yield differed due to N application and in the treatments, but this was only observed with cultivation of maize crop residues in 2009/2010. The combination of ammonium+urea coated with copper sulfate and boric acid optimized grain yield compared to the other urea treatments. The crude protein concentration in maize was not influenced by the technologies of urea coating.

SUMMARYThe physical quality of Amazonian soils is relatively unexplored, due to the unique characteristics of these soils. The index of soil physical quality is a widely accepted measure of the structural quality of soils and has been used to specify the structural quality of some tropical soils, as for example of the Cerrado ecoregion of Brazil. The research objective was to evaluate the physical quality index of an Amazonian dystrophic Oxisol under different management systems. Soils under five managements were sampled in Paragominas, State of Pará: 1) a 20-year-old second-growth forest (Forest); 2) Brachiaria sp pasture; 3) four years of no-tillage (NT4.); 4) eight years of no-tillage (NT8); and 5) two years of conventional tillage (CT2). The soil samples were evaluated for bulk density, macro and microporosity and for soil water retention. The physical quality index of the samples was calculated and the resulting value correlated with soil organic matter, bulk density and porosity. The surface layers of all systems were more compacted than those of the forest. The physical quality of the soil was best represented by the relations of the S index to bulk density and soil organic matter.Index terms: conventional tillage, no-tillage, S Index.(1) Part of the Master´s dissertation of the first author presented at the Universidade Federal Rural da Amazônia -UFRA.Received

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This study aimed to investigate the effect of the foliar application of phosphite and phosphate on growth, phosphorus (P) status, and nutritional aspect of common bean (Phaseolus vulgaris cv. Radiante) plants grown under different soil phosphate levels. Experiment was organized in factorial scheme completely randomized using 2 soil phosphate levels (Pi-starved and Pi-sufficient plants), combined with 3 nutrient sources supplied via foliar application (KH 2 PO 3 , KH 2 PO 4 , and KCl used as control), and 2 foliar application numbers (single and two applications). In this study were measured root dry weight, shoot dry weight, and root to shoot ratio, as well as shoot P concentration, root P concentration, accumulated P in shoot, accumulated P in root, P uptake efficiency, P utilization efficiency, P translocation, and macro and micronutrients in shoot. Common bean growth under limiting phosphate availability in soil exhibited lower biomass yield and higher concentration of nutrients in shoot tissues. The results exhibit foliar-applied KH 2 PO 3 causes harmful effects in phosphate-starved common bean. Either one or two foliar sprays of KH 2 PO 4 were not sufficient to affect the growth and nutrition of the common bean plants, regardless of soil P status.

pela credibilidade, pelo companheirismo, sobretudo, por serem ótimos filhos aos meus pais. Ofereço, A Deus. À Sociedade, principalmente às crianças de hoje e às que hão de nascer! 4 5 AGRADECIMENTOS Ao meu Senhor e Amigo, Jesus Cristo, por transformar a minha vida, permitindo que O conhecesse. Por me fazer feliz de verdade, me dar liberdade e me mostrar que nada é impossível ao que crê! Tudo é dEle, por Ele e para Ele, para sempre! Sei que sem a comunhão com a Trindade Santa, esta conquista não seria possível. Espírito Santo, obrigado por sempre falar ao meu coração! Ao orientador, Prof. Vitti, pelo estímulo, pelos conhecimentos passados e, principalmente, por ter me dito SIM e me fazer acreditar que é possível ter sucesso com humildade! Pelo seu SIM, meu sonho foi possível! Ao Prof. Boaretto pelo estímulo, apoio, pelos conhecimentos passados e, principalmente, pela enorme paciência, colaboração e disponibilidade sempre. Ao Prof. Antonio Rodrigues Fernandes da UFRA, pelos ensinamentos, conselhos e críticas desde a graduação. À Henriqueta, pelos ensinamentos no laboratório e paciência. Ao Dr. Eduardo Stuch da Estação Experimental de Citricultura de Bebedouro, por ter cedido o pomar e acreditado na ideia. Ao Dr. Felipe Carlor Alvarez Villanueva, pela grande e valiosa ajuda com análises isotópicas e principalmente pelo imenso coração generoso. Ao Bat -ria (Thiago), Bahiano (Carlos) e Diego por serem, amigos e enorme colaboração. Às amigas, Cintia, Eva e Robertinha por serem companheiras em todos os momentos, amo vocês! À Pós Doc Fernanda Latanze, pela amizade, apoio, paciência e colaboração neste trabalho. À Silvia Helena, pela amizade, paciência e carinho! À Vanessa, química da empresa Intercuf ® pelo preparo de todos os produtos marcados.