Productive, nutritional and metabolic characteristics of marandu palisadegrass grown with nitrogen and magnesium rates / Características produtivas, nutricionais e metabólicas do capim-marandu submetido a doses de nitrogênio e magnésio

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

Productive, nutritional and metabolic characteristics of the forage plants may be changed by the nitrogen and magnesium availability. The objective was to study the effects of nitrogen and magnesium rates on marandu palisadegrass growth, by evaluating the shoot and root yield, leaf and root concentrations of nutrients and leaf concentration of inorganic forms of nitrogen, glutamine synthetase activity and nitrogen:magnesium ratio in recently expanded leaf laminae (RL). The experiment was carried out in a greenhouse at Piracicaba, State of São Paulo, Brazil, with the Brachiaria brizantha cv. Marandu. Five nitrogen rates (2, 9, 16, 23 and 30 mmol L-1) and five magnesium rates (0.05, 0.70, 1.35, 2.00 and 2.65 mmol L-1) were used in nutrient solutions, in a fractorial 52 factorial, resulting in the following combinations: 2/0.05, 2/1. 35, 2/2.65, 9/0.70, 9/2.00, 16/0.05, 16/1.35, 16/2.65, 23/0.70, 23/2.00, 30/0.05, 30/1.35 and 30/2.65. A randomized block design, with four replications was used. Plants had a growth and regrowth period. After the second harvest it was evaluated the dry mass yield, number of tillers and leaves, sampled fresh material to assay the glutamine synthetase activity, measured the leaf area, and determined the concentrations of nutrients, nitrate and ammonium in the recently expanded leaf laminae (diagnostic leaves). After the second harvest the roots were separated from the tops and was determined the root dry mass, total length and surface, specific length and surface, and concentrations of nutrients in such plant tissue. High nitrogen and magnesium rates resulted in high dry mass yield, leaf area, number of leaves and tillers, in both growth periods of the grass, as well as in roots dry mass, length and surface. Nitrogen (at the second harvest) and calcium (both harvests) concentrations in diagnostic leaves and nitrogen concentration in the roots was high when high rates of nitrogen nitrogen were combined with high rates of magnesium. Diagnostic leaves, in the two grown periods, and roots sampled had low potassium concentrations in plants growth with high rates of both nitrogen and magnesium. Increases in nitrogen rates increased nitrogen concentration in the diagnostic leaves and calcium concentration in the roots, and decreased root specific length and surface. Increases in magnesium rates increased magnesium concentration in the diagnostic leaves and roots, but decreased root calcium concentration and root specific length and surface. Ammonium concentration was increased by nitrogen rates and nitrate concentration was higher under magnesium deficiency. Glutamine synthetase, determined at the two growth periods, decreased with increasing nitrogen rates. Maximum dry mass yield in the first harvest of the grass was found when the nitrogen and magnesium concentrations ratio was 6.3:1 in the diagnostic leaves.

ASSUNTO(S)

marandu palisadegrass nitrogênio magnesium nitrogen. 5. plant nutrition 6. root system 7. tissue analysis diagnose foliar nutrição vegetal magnésio graminaceous forage plants gramíneas forrageiras capim marandu sistema radicular

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