Mudanças nas frações lábeis de fósforo no solo em função da aplicação de fertilizantes minerais e organominerais fosfatados.

A produção de fertilizantes organominerais a partir resíduos orgânicos como, por exemplo, a cama de frango tem se tornado uma prática comum, visto os benefícios econômicos e ambientais. O uso de fertilizantes organominerais pode alterar a dinâmica das formas de fósforo (P), visto a sua natureza física e química. No entanto, estudos sobre o tema ainda são incipientes. Dessa forma, objetivou-se com esse estudo avaliar as frações lábeis de P no solo sob aplicação de fertilizante organomineral comparado a uma fonte mineral em doses crescentes de P (0, 125, 250, 375 e 500 mg por vaso). As frações lábeis de P no solo aumentaram significativamente com as doses de P, contudo, não houve diferenças entre os fertilizantes (exceto, na dose de P de 375 mg por vaso). Esse estudo traz informações relevantes acerca das transformações de P no solo permitindo aperfeiçoar e fomentar o uso de fertilizantes organominerais fosfatados

Effects of molybdenum, nickel, and nitrogen sources on the mineral nutrition and growth of rice plants.

The aims of the current work were to measure the effect of Mo and Ni on dry-matter yield of rice plants supplied with two N sources (ammonium nitrate and urea) and to evaluate the influence of Mo and Ni on variables related to dry-matter yield, such as activity of both urease and nitrate reductase, chlorophyll, net photosynthesis rate, total N, nitrate content, and Mo and Ni concentrations in roots and shoots

Nitrogen metabolism in coffee plants in response to nitrogen supply by fertigation.

Coffee plants require high application rates of nitrogen (N) to produce coffee beans. However, information regarding plant N uptake and assimilation under intensive high-technology cultivation systems is scarce, a situation which restrains the maximizing productivity with minimal N rates. The aim of this study was to evaluate N assimilation enzymes such as nitrate reductase (EC 1.6.6.1), glutamine synthetase (EC 6.3.1.2), urease (EC 3.5.1.5), and N compounds of coffee plants during a phenological cycle in response to N applied by fertigation. Our study was carried out with 7-year-old trees of Coffea arabica L., under a center pivot sprinkler irrigation and fertigation system, with five N rates (0, 200, 400, 600, and 800 kg ha−1) applied to the coffee field. The results of the present study suggest that both N metabolism enzymes, and the content of nitrate and ammonium in coffee were directly related to the phenological cycle. The N fertigation rates are correlated with the N and amino acid contente. Nitrate reductase and urease showed higher activities before anthesis and during grain filling. Glutamine synthetase showed highest activities during rapid grain expansion. The data also indicate that there is merit in gaining greater understanding of N metabolism in coffee plants grown under high-intensive systems. There is therefore merit in conducting further research on how monitoring the N assimilation enzymes might be used to improve fertilizer management of coffee in commercial orchards

Physiological, biochemical, and ultrastructural characterization of selenium toxicity in cowpea plants

Selenium (Se) is considered a beneficial element for plants; however, in high concentrations, it causes negative effects on plant physiology and development. This study reports the first physiological, nutritional, and ultrastructural description of Se toxicity in cowpea growing under field conditions. Selenium was supplied as a foliar application of sodium selenite at varying concentrations (0, 50, 100, 200, 400, 800, 1200, and 1600 g ha−1). An increased yield was observed with the application of 50 g ha−1 Se. Application of concentrations higher than 50 g ha−1 caused leaf toxicity. Increased lipid peroxidation and hydrogen peroxide concentration and reduced total sugars, sucrose, and carotenoid concentration were observed at highest doses tested (1200 and 1600 g ha−1). Applications of more than 50 g ha−1 Se reduced the phloem diameter, caused chlorosis of the leaf blade with a coalescence of lesions, and caused pink salt deposits to appear. Lesions were observed mainly near the trichomes on the adaxial surface of the leaf blade. An analysis of the element distribution with microprobe X-ray fluorescence spectrometry (μ-XRF) revealed accumulation of Se, calcium (Ca), potassium (K), copper (Cu), and manganese (Mn) near the primary vein and in the necrotic brown areas of the leaf lesions. In contrast, Na was homogeneously distributed in the leaf tissue