Atividade da urease e crescimento de alface no solo em resposta a níquel

• Autor(a) principal: Oliveira, Thomas Carlos de
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5416
• topic: Niquel; Urease; Alface; Nickel; Urease; Lettuce; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

The studies with Ni in soils and plants, in general, are more related to its toxicity effects to plants with emphasis in the hability of Ni hyperacumulator plants to tolerate high Ni concentrations. In recent years, this approach has been changed with more attention to the Ni participation in the plant mineral nutrition. It has to be noted that Ni is related to the plant N metabolism, due to its participation in the activity of the enzyme urease which mediate the transformation of urea in NH3 and CO2. The aim of this research was to evaluate the growth of lettuce (Lactuca sativa L.) in response to soil Ni fertilization; the effects of Ni in the urease activity in plants supplied with urea (CO(NH2)2) and ammonium nitrate (NH4NO3) as N sources; to compare the efficiency of Mehlich-3 and DTPA extractions in the determination of Ni availability in a Red-Yellow Latossol (Oxysol). The experiment was set as a 2 x 8 (2 N sources: CO (NH2)2 and NH4NO3; 8 Ni doses: 0, 2, 4, 8, 12, 16, 24 and 32 mg/dm3) with 5 replications, in an entirely ramdomly block design. The experimental unity was a 3 dm3 plastic vase with soil, treatments and two lettuce plants. Nitrogen (200 mg/dm3) was supplied as urea (Ur) or ammonium nitrate (AN), half in the seedling and half surface dressed, and Ni was supplied as NiCl2 at the seedling. One lettuce plant, per vase, was harvested 63 days after seedling and oven dried for the determination of the dry matter mass (DM) and analysis of the plant mineral composition. One week later, the other plant was harvested and its fresh matter used for the determination of urease activity by the method of indophenols. In the dry matter it was determined the dry matter contents of K, Ca, Mg, Mn, Cu, Zn, Ni (nitric-perchloric digestion and ICP-OES dosage) and N by the Kjeldahl method. In the soil it was determined the available Ni by Mehlich-3 and DTPA extractions and AAS dosage. The analysis of variance of the data was made and regression equations were adjusted for dry matter production, urease activity, soil nutrient and plant nutrient concentrations, as a function of the Ni doses applied to soil, for each N source, Ur and NA. Analysis of correlation was made between the concentrations and contents of Ni in the lettuce leaves and soil extracted Ni by Mehlich-3 and DTPA. Additionally, linear regression equations were adjusted for the plant Ni contents and the Mehlich-3 and DTPA soil recovered Ni, as a function of the Ni doses applied to soil. There was significant difference in the dry matter yield between theplants supplied by different N sources (5.07 g/plant mean for NA supplied plants and 4.20 g/plant mean for Ur supplied plants). For Ni doses applied to soil there was no significant difference in the lettuce dry matter yield whereas for the urease activity there was increase as Ni was added to soil. There was no difference between the N sources (Ur and AN) as related to the urease activity in the lettuce leaves. Smaller N concentration was detected in plants grown under the AN soil treatments, which was probably caused by a dilution effect. The total N in the plants was uniform in response to the increased Ni doses applied to the soil. The amounts of Ni recovered by Mehlich-3 and DTPA from the Red-Yellow Latossol increased as a function of the increase in the soil applied Ni. The higher correlation was shown between the Ni extracted from soil with Mehlich-3 and the plant Ni contents and concentrations. The bigger difference between the results from Mehlich-3 and DTPA soil extraction was shown in the treatments with AN added to soil.