Nine soils with distince properties and Se levels were selected to test a fractionation procedure of soil Se based on sequential extraction.Soil Se was fractionated into readily available Se(fraction I,extracted by 0....Nine soils with distince properties and Se levels were selected to test a fractionation procedure of soil Se based on sequential extraction.Soil Se was fractionated into readily available Se(fraction I,extracted by 0.5 M NaHCO3),slowly available Se(fraction II,extracted by 0.1 M NaOH-0.1 M Na4P2O7),amorphous oxide-occluded Se(fraction Ⅲ,extracted by acid ammonium oxalate)free oxide-occluded Se (fraction VI,extracted by dithionite-citrate-bicarbonate buffer solution)and residual Se(fraction V,determined by NHO3-HClO4 digestion of the final soil residue).The recovery of soil Se(the sum of all fractions over total soil Se determined independently)by this procedure was from 88.1% to 110.9%,mean 99.2%±6.4% for the test soils.The sum of fractions I and II,provided a good measure of available Se in soils and the percentage of fraction I plus II over the total soil Se,tentatively defined as Se availability index.could be used to indicate soil Se status and predict Se deficiency.展开更多
Effects of citrate and tartrate on phosphate adsorption and desorption from kaolinite,goethite,amorphous Al-oxide and Ultisol were studied.P adsorption was significantly decreased as the concentration of the organic a...Effects of citrate and tartrate on phosphate adsorption and desorption from kaolinite,goethite,amorphous Al-oxide and Ultisol were studied.P adsorption was significantly decreased as the concentration of the organic anions increased from 10^-5 to 10^-1 M.At 0.1 M and pH 7.0,tartrate decreased P adsorption by 27.6%-50.6% and citrate by 37.9-80.4%,depending on the kinds of adsorbent.Little Al and/or Fe were detected in the equilibrium solutions,even at the highest concentration of the organic anions.Effects of the organic anions on phosphate adsorption follow essentially the competitive adsorption mechanism.The selectivity coefficients for competitive adsorption can be used to compare the effectiveness of different organic anions in reducing P adsorption under given gonditions. Phosphate desorption was increased by 3 to 100 times in the presence of 0.001 M citrate or tartrate compared to that in 0.02 M KCl solution alone.However,for all the soil and clay minerals studied the amount of P desorbed by citrate or tartrate was generally lower than or close to that of isotopically exchangeable P.The effect of organic anions on phosphate desorption arises primarily from ligand exchange.展开更多
文摘Nine soils with distince properties and Se levels were selected to test a fractionation procedure of soil Se based on sequential extraction.Soil Se was fractionated into readily available Se(fraction I,extracted by 0.5 M NaHCO3),slowly available Se(fraction II,extracted by 0.1 M NaOH-0.1 M Na4P2O7),amorphous oxide-occluded Se(fraction Ⅲ,extracted by acid ammonium oxalate)free oxide-occluded Se (fraction VI,extracted by dithionite-citrate-bicarbonate buffer solution)and residual Se(fraction V,determined by NHO3-HClO4 digestion of the final soil residue).The recovery of soil Se(the sum of all fractions over total soil Se determined independently)by this procedure was from 88.1% to 110.9%,mean 99.2%±6.4% for the test soils.The sum of fractions I and II,provided a good measure of available Se in soils and the percentage of fraction I plus II over the total soil Se,tentatively defined as Se availability index.could be used to indicate soil Se status and predict Se deficiency.
文摘Effects of citrate and tartrate on phosphate adsorption and desorption from kaolinite,goethite,amorphous Al-oxide and Ultisol were studied.P adsorption was significantly decreased as the concentration of the organic anions increased from 10^-5 to 10^-1 M.At 0.1 M and pH 7.0,tartrate decreased P adsorption by 27.6%-50.6% and citrate by 37.9-80.4%,depending on the kinds of adsorbent.Little Al and/or Fe were detected in the equilibrium solutions,even at the highest concentration of the organic anions.Effects of the organic anions on phosphate adsorption follow essentially the competitive adsorption mechanism.The selectivity coefficients for competitive adsorption can be used to compare the effectiveness of different organic anions in reducing P adsorption under given gonditions. Phosphate desorption was increased by 3 to 100 times in the presence of 0.001 M citrate or tartrate compared to that in 0.02 M KCl solution alone.However,for all the soil and clay minerals studied the amount of P desorbed by citrate or tartrate was generally lower than or close to that of isotopically exchangeable P.The effect of organic anions on phosphate desorption arises primarily from ligand exchange.
