Zinc Adsorption by Sterilized and Non-Sterilized Soil in the Presence of Citrate and Catechol

The effect of organic ligands on zinc (Zn) adsorption in the rhizosphere may be influenced by microbial activity depleting the concentration of the ligand over time. Zinc adsorption by sterile and non-sterile lateritic soil was measured by shaking the soils with Zn solutions at a soil-liquid ratio of 1: 5 for five periods of time ranging from 17-480 h. The concentrations of Zn and the ligands were determined after the selected times. The speciation of Zn was then estimated. Changes in Zn adsorption with time in the presence of organic ligands were due to changes in pH and Zn complexation associated with the addition and breakdown of the organic ligands and with the technique of sterilization. Zinc adsorption was higher in non-sterile than in sterile soil. Adsorption in the presence of citrate was lower than in its absence except in non-sterile soil after 72 h. The adsorption in the presence of catechol was similar to that in its absence

The Effect of Citrate and pH on Zinc Uptake by Wheat

Zinc uptake by plants may be influenced by its reaction with organic ligands in the rhizosphere. Therefore, four experiments were conducted to examine the effects of an organic ligand (citrate) and pH on the uptake of Zn by wheat (Triticum aestivum L. emend. Thell). Plants were grown for 21 to 28 d in a nutrient solution (containing 0-0.05 µmol L-1 Zn) in a temperature controlled tank, either in the absence or presence of citrate and at constant or variable pH (3.7-7.1). Dry matter weights of plant parts and Zn content in the shoots were determined. The activities of Zn in the nutrient solution were estimated. Shoot dry matter of the wheat plants in each experiment correlated well with either ZnT/[H+] or E(moles Zn/charge)/[H+] (ZnT = total Zn, Zn1 = each zinc species). Both parameters could explain the relative shoot dry matter of the plants from all experiments in one equation (y = A + BE -cx; r2 = 0.79 and 0.77, respectively). In the absence of citrate, shoot dry matter as well as Zn content increased with increasing pH and increasing total Zn concentrations in solution. In the presence of citrate, the shoot dry matter of wheat plants that were grown in nutrient solution with constant pH increased with the total Zn concentrations. However, the effect of the total Zn concentrations in the solution containing citrate with variable pH were less important than the effect of p

Zinc Adsorption by a Lateritic Soil in the Presence of Organic Ligands

Zinc adsorption by a lateritic podzolic soil was measured in the presence of 0 to 3 mmol/litre of acetate, oxalate, citrate, tricarballylate, salicylate, or catechol, or 0 to 3 mmolc/litre of humate. Zinc remaining in solution was measured by atomic absorption spectrometry after shaking the soil for 17 h at a soil/liquid ratio of 1:5 in a 0.003 mol/litre KCl solution containing 0 to 500 μmol/litre Zn and the ligands. In the absence of organic ligands, more than 95% of the zinc was adsorbed. The amount of adsorption was linearly correlated with pH and the concentration of ZnOH+ in solution after shaking (r² = 0.98). Zinc adsorption and pH decreased in the presence of each of the ligands except catechol. Seventy four percent of the variation in adsorption was accounted for by the combined effects of the concentration of zinc-ligand complex (Zn-L) and the concentration of ZnOH+ that were present in solution after adsorption. However, other factors such as changes in the number of sites available for adsorption, the point of zero salt effect of the soil, and the change of zinc species also contributed to the magnitude of zinc adsorption

Yield and postharvest quality of winter growing crisphead lettuce as affected by doses of nitrogen and molybdenum Rendimento e qualidade pós-colheita de alface americana em função de doses de nitrogênio e molibdênio

The trial was carried out at Três Pontas, Minas Gerais State, Brazil, from April to July 2003, to evaluate the influence of nitrogen and molybdenum rates on productive characteristics and postharvest quality of crisphead lettuce (Lactuca sativa L.). A randomized complete block design with three replications was used. Treatments were a factorial combination of four nitrogen rates (0.0; 60.0; 120.0 and 180.0 kg ha-1) applied in additional the dose commonly used by growers (60 kg ha-1 of N) and five foliar molybdenum rates (0.0; 35.1; 70.2; 105.3 and 140.4 g ha-1). The total and commercial fresh weight and head circumference showed significant effects for doses of nitrogen and of molybdenum, as well as for their interaction. No significant effects of the treatments for stem length were observed. There was a linear effect of N and Mo doses for postharvest conservation at 28 days, and the rate of 150.0 kg ha-1 of N showed the best conservation at 35 days after the harvest. The percentage of dry matter showed quadratic effects, and the doses of 95.9 kg ha-1 of N and 75.3 kg ha-1 of Mo showed the highest return.<br>O trabalho foi conduzido no município de Três Pontas, Sul de Minas Gerais, de abril a julho de 2003, com o objetivo de avaliar a influência de doses de nitrogênio e molibdênio nas características produtivas e qualidade pós-colheita da alface tipo americana (Lactuca sativa L.). Utilizou-se o delineamento de blocos ao acaso em arranjo fatorial 4x5, compreendendo quatro doses de nitrogênio em cobertura adicionais à dose aplicada pelo produtor de 60 kg/ha de N (0; 60; 120 e 180 kg ha-1) e cinco doses de molibdênio via foliar (0,0; 35,1; 70,2; 105,3 e 140,4 g ha-1) com três repetições. As massas fresca total e comercial e a circunferência da cabeça evidenciaram efeitos significativos para doses de nitrogênio em cobertura e de molibdênio, assim como para sua interação. Não se observou efeito significativo dos tratamentos para comprimento do caule. Houve uma resposta linear para doses de N e Mo para conservação pós-colheita aos 28 dias, sendo que a dose de 150,0 kg ha-1 de N em cobertura promoveu a melhor conservação aos 35 dias após a colheita. A dose de 95,9 kg ha-1 de N em cobertura e a dose 75,3 kg ha-1 de Mo propiciariam o maior retorno em termos de percentagem de massa seca