CHARACTERIZING PLANT UPTAKE OF CADIUM AND ZINC FROM SOILS TREATED WITH SEWAGE SLUDGE (DIFFUSION, MECHANISTIC MODEL, CORN, SENSITIVITY ANALYSIS)
Abstract
Field and laboratory studies were conducted to characterize the uptake of Cd and Zn by corn (Zea mays L.) seedlings grown in soils treated with sewage sludge. Kinetic parameters describing uptake of Cd and Zn were determined for intact corn seedlings grown for 15 and 22 days in nutrient solutions containing levels of Cd and Zn representative of those found in soil solutions. Soil samples were obtained from sites in Indiana, Michigan, Ohio, and Wisconsin where the same sewage sludge had been applied to provide 19 kg Cd and 340 kg Zn ha('-1). Based on growth chamber studies sludge addition increased plant uptake of Cd and Zn but it did not affect shoot or root weight, root length, or other root properties of corn seedlings grown in the untreated and sludge treated soils for 16 and 22 days. The addition of sludge increased the adsorbed Cd and Zn and the concentration of Cd and Zn in the soil solution of all 4 soils. There was no effect of sludge on diffusion coefficients (De) for Cd or Zn, but there was an inverse relationship between De for Zn and soil pH. A mechanistic uptake model gave a reasonable prediction of Cd (r = 0.81) and Zn (r = 0.91) uptake by corn seedlings growing in the untreated and sludge treated soils. Sensitivity analyses conducted with the model showed that plant factors having the greatest influence on Cd and Zn uptake include the root growth constants, average root radius and water influx rate while the effect of influx kinetics and half distance between roots was small. Cadmium and Zn in soil solution affected predicted Cd and Zn uptake more than the adsorbed metal and diffusion coefficient. Soil supply parameters affected Cd and Zn uptake more than influx kinetics. Two computer programs (CHELATE and GEOCHEM) based on chemical equilibria were compared for calculation of chemical species in xylem exudates. Data for phloem exudates from Yucca (Yucca flaccida Haw.) were compiled from available literature and analyzed with GEOCHEM. Oxalate and amino acids were the most important organic ligands in the phloem exudates.
Degree
Ph.D.
Subject Area
Agronomy
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