Metabolismo nitrogenado e biomassa do capim Tifton 85 submetido ? nutri??o n?trica ou amoniacal

• Autor(a) principal: Barbieri Junior, ?lio
• Data de Publicação: 2012
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFRRJ
• Texto Completo: https://tede.ufrrj.br/jspui/handle/jspui/3522
• topic: Cynodon spp. Amino?cidos livre; Atividade da nitrato redutase; Teor A??cares sol?veis; Cynodon spp. Free amino acids; Nitrate-reductase activity; Soluble sugars content; Zootecnia

The responses of forage plants to nitrogen nutrition depends not only on the amount of nutrient available but also its chemical form, as NH4+ or NO3-. Both forms may be absorbed and metabolized with different consequences for the plant productivity. Some species have ecological preference for one or another form, whereas for higher production most use in combination forms. To verify the metabolic behavior and productive of the Tifton 85 in relation to forms and levels of mineral N, two experiments were carried at the Institute of Agronomy, Universidade Federal Rural do Rio de Janeiro (UFRRJ), RJ-Serop?dica. The first experiment was conducted in a growth chamber type phytotron under controlled conditions, using hydroponics and lasted 35 days, counted from a uniformity cut (DAC). Treatments consisted of two forms of N: NH4+ (ammonium sulfate) and NO3- (nitrate Ca, Mg and K) combined with four levels of application: 0.5, 2, 5 and 10 mM, respectively, and four dates sampling at 14, 21, 28 and DAC 35. The second experiment was carried out in a greenhouse, using as growth substrate, soil from the surface horizon of a Haplic Planossolo, occurring in the area under cultivation UFRRJ and Tifton 85. We used a single source of N, representative of the two forms (ammonium nitrate) applied at four rates (0, 80, 160 and 240 mg N kg -1 soil) and assessed four times (at 14, 21, 28 and 35 DAC). In both experiments, treatments were repeated four times. We made to the following determinations: fresh and dry mass of roots, shoots and total concentrations of total-N, N-soluble (N-NO3-, N-NH4+ and N-amino free); activity of nitrate reductase and soluble carbohydrates in 80% ethanol, all determined in leaf blades, sheaths, stems and roots, and leaf chlorophyll content (extracted with N, N-dimethylformamide) and still determined chlorophyll. Regarding the isolated forms of inorganic N, Tifton 85 grass responded to ammonium nutrition, nutrition in relation to nitrate, with increased production of fresh and dry weight total, largest fraction of the total biomass allocation to roots, higher total chlorophyll content and higher levels of soluble sugars and amino acids in leaves and roots. Additionally, showed low concentrations of N-NH4+ in all compartments of plants, even at high doses of N. From the nutritional point of view, the concentrations found for N-NO3-, even in higher doses of N offer no risk of intoxication of ruminant animals. As the use of mixed form (NO3NH4), the metabolic behavior of plants under treatment maximized the production of biomass and reproduced traits similar to those seen in purely ammoniacal nutrition, including increased production of chlorophyll, and preferential allocation of soluble sugars and amino acids in roots and culms. Nutrition mixed assimilation not increased efficiency compared to the use of nitrate or ammonium nutrition. It was concluded that a nutrition 100% ammonia or 50% NO3-+ NH4+, resulted higher in efficiency assimilation of N, nutrition than 100% nitric, this phenomenon is not documented.