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.

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.

The low nutrients levels available in pasture formation reduces the forage yield. Soil correction and fertilization practices are considered priorities in the planning, renovation or recovery of pastures. The aimed of this experiment was to evaluate the effect of nitrogen and phosphate fertilization rate in productivity of the Panicum maximum cv. BRS Zuri. The experimental design was a randomized block design in a 3×4 factorial arrangement, with three doses of superphosphate (0.0, 80.0 and 160.0 kg.ha-1) and four doses of ammonium nitrate (0.0; 20.0; 40.0 and 60.0 kg.ha-1), with three replicates. The following parameters were evaluated at 120 days after implantation: green mass and dry matter yield, plant height, number of plants and tillers per square meter. The doses of 80.0 and 160.0 kg.ha-1 of P2O5 and 60.0 kg.ha-1 of nitrogen combined to each other showed the best results for forage yield.

Human zinc malnutrition is a concern in the contemporary scenario. Ranked among the serious micronutrient deficiencies and considered a major cause of child mortality, especially in developing countries. Cereals, such as maize (Zea mays L.), food source in these countries, show low zinc concentration. In view of this, biofortification has been shown promise to increase the nutrient content in staple foods and to improve their nutritional quality. The aim of this study was to evaluate the potential of maize genotypes in relation to yield and zinc concentration in grains and leaves as a function of zinc sulfate doses in two growing seasons. A total of 17 commercial hybrids were evaluated in three doses (0, 5, and 10g L-1 ha-1). The zinc concentration was quantified by acid digestion, followed by atomic absorption spectrophotometer analysis. Any change was observed in grain yield as a function of the doses. Higher doses applied near flowering resulted in higher concentrations of the micronutrient in the grains. However, the concentrations in the grains were, on average, below the value established by the Harvest Plus biofortification program. The results provide information for the selection of genotypes with zinc uptake potential aiming at food safety through agronomic biofortification.

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