Under P deficiency amino acids in the root exudates increased from 104.5 to 248.5 umol/plant, which contrasted sharply with the almost 4-fold decrease under N deficiency (104.5-25.1 zmol/ plant; 1). Graham et al. (5) observed P deficiency to result in a 3-fold increase in amino acid exudation with only a concentration increase of 60% within the root.The effective study of the rhizosphere has been limited in the past due to the difficulty of isolating root effects from general soil and microbiological effects and quantifying those effects. The objective of this research was to identify and measure the effect of P deficiency upon the exudation of organic acids by the growing aseptic roots of alfalfa (Medicago sativa L.) seedlings.
Transformation of soil lead (Pb) to pyromorphite, a lead phosphate, may be a cost-effective remedial strategy for immobilizing soil Pb and reducing Pb bioavailability. Soil treatment using phosphoric acid (H3PO4) was assessed for its efficacy to reduce Pb solubility and bioaccessibility. Soil containing 4,360 mg of Pb kg(-1), collected from a smelter-contaminated site in Joplin, MO, was reacted with 1,250, 2,500, 5,000, and 10,000 mg of P kg(-1) as H3PO4. The reaction was followed by measurements of Pb bioaccessibility, solubility products, and microprobe analyses. Soluble Pb concentration in the soil decreased with increasing H3PO4 addition. Adding 10,000 mg of P kg(-1) reduced bioaccessible Pb by 60%. The logarithm of bioaccessible Pb decreased as a linear function of increasing H3PO4 addition with an R2 of 0.989. A higher soil/solution ratio was required to extract bioaccessible Pb after the treatment. Microprobe analyses showed that the Pb particles contained P and Cl after the reaction, and the spectra generated by the wavelength-dispersive spectrometer were similar to those of synthetic chloropyromorphite. Lead solubility in the P-treated soil was less than predicted for hydroxypyromorphite [Pbs(PO4)3-OH] and greater than predicted for chloropyromorphite [Pbs(PO4)3Cl]. The P treatment caused approximately 23% redistribution of soil Pb from the clay and silt size fractions to the sand fraction. Soil treatment with H3PO4 resulted in the formation of a compound similar to chloropyromorphite and reduced bioaccessibility of soil Pb, which may have a potential as an in situ technique for Pb-contaminated soil remediation.
A method for the determination of S in plant materials is described. The material is oxidized by nitric and perchloric acid using a heating block to reduce perchloric acid loss. The SO 4 content of the solution is determined turbidimetrically as BaSO 4 . The proposed method has been found to be more accurate and rapid than the conventional dry ashing procedures for the determination of S in plant material.
Fertilization with KCI can induce a CI toxicity that dE:creases the yi,eld of soybean (Glycine 11UlX (L.) Merr.]. The objective nf this study was to see if CI toxicity can be avoided by selecting cultivars that take Ull less CI from tbe soil. Sixty soybean cultivars, 12 each from Maturity Groups II, III, IV, V, and VI were grown on a Mexico silt loam (fine, montmorillonitic, mesic Udollic Ocbraqualt) without added CI or with 673 kg CI ba -• added as CaCI 1 • The addition of <:I increased the mean CI concentration of all cultivars from 1.5 to 18.8 g CI kg·' at 15 d and from 0.4 to 1.3 g CI kg-' at 80 d. AII36 cultivars from MG II, III, and IV, along witb 5 cultivars from MG V and VI, bad significantly higher concentrations of CI in leaves than did 19 cultivars from MG V and VI. Cultivars with high CI concentrations were referred to as accumulators and those with low concentrations as excluders. The occurrence of leaf scorch, a symptom of CI tm:icity, in CI accumulator cultivars was significantly higher than in Cl excluder cultivars. Leaf scorch ratings were positively correlated witb CI concentrations of soybean leaves at 15 and 80 d. Chloride com,centrations in tbe leaves were higher (accumulators, 24.3 g kg-'; exduders, 7.0 g kg-') at tbe early growth stages than in tbe later stag1:s (accumulators, 1.8 g kg-'; excluders, 0.3 g kg-'). Addition ofCaCI 1 increased CI concentrations in seeds of Essex, an accumulator cultivar, but bad no significant effect on oil and protein content. The average grain yields of Cl accumulator cultivars were significantly decreased by 16% due to Cl addition, while grain yields of excluder cultivars were not significantly reduced. Cultivar selection in MG V and VI may be a means of minimizing CI effects associated witb muriate of potash fertilization.
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