While P sorption in mineral soils has been extensively studied, P sorption behavior in organic‐rich soils is less known. This study was conducted to determine the relationships between Langmuir P sorption maxima (Smax) and selected physicochemical properties of soils, with particular emphasis on organic matter (OM) content. The Smax values were determined for 72 soil samples from the North Carolina Coastal Plain, along with pH, clay and OM contents, oxalate‐extractable P (Pox), Al (Alox), and Fe (Feox), and Mehlich 3 extractable P (PM3), Al (AlM3), and Fe (FeM3). Path analysis was used to examine direct and indirect effects of soil properties on Smax In the oxalate path analysis, the direct effects of clay, Alox, and Feox on Smax were significant in the order Alox > clay > Feox (P < 0.05). The Smax was highly influenced by the indirect effect of Alox and Feox through OM content. A two‐piece segmented linear relationship existed between Smax and OM and the regression slope in soils with OM ≤ 49 g kg−1 was 10‐fold greater than that for soils with OM > 49 g kg−1 This finding suggested that noncrystalline or organically bound Al and Fe in the soils with OM > 49 g kg−1 is less effective for P sorption than in the soils with lower OM content. In the Mehlich 3 path analysis, the direct effects of clay, OM, and AlM3 on Smax were significant in the order AlM3 > OM > clay (P < 0.05) while the direct effect of FeM3 on Smax was not significant. Oxalate may be better suited than Mehlich 3 as an extractant for predicting P sorption capacity in the Coastal Plain soils.

No abstract

No abstract

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Path Analysis of Phosphorus Retention Capacity in Allophanic and Non-allophanic AndisolsSoil Chemistry P hosphorus retention capacity is an important property controlling the release of P from soil to surface water. Phosphorus retention in acidic soils is primarily regulated by Al and Fe in clay minerals (Kang et al., 2009;Zhang et al., 2005). Both Al and Fe minerals are abundant in volcanic ash soils that are characterized by a high PRC (Shoji and Ono, 1978;Wada and Gunjigake, 1979). To understand P retention behavior in soils, the chemical fractionation of Al and Fe is more critical than the total amount existing in the soil. Hiradate and Uchida (2004) grouped the chemical forms of Al and Fe into (i) humus complexes, (ii) non-and poorly crystalline metal hydroxides (e.g., allophane and ferrihydrite), (iii) crystalline metal (hydr)oxides (e.g., gibbsite and goethite), and (iv) stable minerals (e.g., phyllosilicates). Non-and poorly crystalline Al and Fe hydroxides, which can selectively be extracted by acid ammonium oxalate solution (Al ox and Fe ox ), are known to be the major P sorbent in noncalcareous soils (McKeague and Day, 1966;Schoumans, 2000). Th e fractions of Al p and Fe p represent metal-humus

The objective of this study was to investigate the concentration and chemical species of Zn, Cu, and P in the bulk soil and water-dispersible colloid (WDC) fraction collected from a field where swine manure (SM) compost has been continually applied for 23 years. A filtration and ultracentrifugation process was used to separate and collect WDC (20−1000 nm) from the soil. The continual application of SM increased soil P from 1.6 to 4.5 g kg −1 , Zn from 109 to 224 mg kg −1 , and Cu from 87 to 95 mg kg −1 for 23 years. The continual SM compost application also enhanced the formation of soil WDC in which Zn (215 mg kg −1 ) and Cu (62 mg kg −1 ) were highly accumulated and P (25 g kg −1 ) was greater than in the bulk soil. According to the result of X-ray absorption spectroscopy (XAS), the continual application of SM compost increased P associated with Fe hydroxides in the soil and WDC fraction. Iron K-edge XAS revealed the dominance of goethite and ferrihydrite in the WDC fraction, suggesting that P was bound to these (oxy)hydroxides. Copper K-edge XAS determined the dominance of Cu(II) associated with humus in the soil and WDC fraction. For Zn species in the SM-compost-applied soil, hopeite and Zn associated with humus were accumulated in the bulk soil, whereas Zn associated with humus was the primary species in the WDC fraction. Our study suggests that the formation of organic complexes in the WDC fraction could enhance the mobility of Zn and Cu as the repeated application of SM compost continues.

Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM-hyamine complex. The PAM calibration curve with DI water showed a strong linear relationship (r 2 = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L -1 . Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship (r 2 > 0.97) and lowest detection limit (0.3 to 1.2 mg L ). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites.

No abstract

No abstract