TECHNICAL REPORTS: SURFACE WATER QUALITY TECHNICAL REPORTS
Using Rare Earth Elements to Control Phosphorus and Track Manure in Runoff Anthony R. Buda,* Clinton Church, Peter J.A. Kleinman, Lou S. Saporito, and Barton G. Moyer USDA–ARS Liang Tao Chinese Academy of Sciences
Concern over the enrichment of agricultural runoff with phosphorus (P) from land applied livestock manures has prompted the development of manure amendments that minimize P solubility. In this study, we amended poultry, dairy, and swine manures with two rare earth chlorides, lanthanum chloride (LaCl3⋅7H2O) and ytterbium chloride (YbCl3⋅6H2O), to evaluate their effects on P solubility in the manure following incubation in the laboratory as well as on the fate of P and rare earth elements (REEs) when manures were surface-applied to packed soil boxes and subjected to simulated rainfall. In terms of manure P solubility, La:water-extractable P (WEP) ratios close to 1:1 resulted in maximum WEP reduction of 95% in dairy manure and 98% in dry poultry litter. Results from the runoff study showed that REE applications to dry manures such as poultry litter were less effective in reducing dissolved reactive phosphorus (DRP) in runoff than in liquid manures and slurries, which was likely due to mixing limitations. The most effective reductions of DRP in runoff by REEs were observed in the alkaline pH soil, although reductions of DRP in runoff from the acidic soil were still >50%. Particulate REEs were strongly associated with particulate P in runoff, suggesting a potentially useful role in tracking the fate of P and other manure constituents from manure-amended soils. Finally, REEs that remained in soil following runoff had a tendency to precipitate WEP, especially in soils receiving manure amendments. The findings have valuable applications in water quality protection and the evaluation of P site assessment indices.
Copyright © 2010 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 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. J. Environ. Qual. 39:1028–1035 (2010) doi:10.2134/jeq2009.0359 Published online 9 Mar. 2010. Received 30 Oct. 2009. *Corresponding author (
[email protected]). © ASA, CSSA, SSSA 5585 Guilford Rd., Madison, WI 53711 USA
C
oncern over agriculture’s role in accelerating eutrophication of freshwaters and estuaries has prompted federal and state nutrient management regulations guiding land application of livestock manure (Sims and Kleinman, 2005). Nearly all U.S. states have adopted the P Index, which targets fields for P-based management founded on an understanding of “source” and “transport” variables (Sharpley et al., 2003). In response, considerable research has been directed at developing manure amendments to address P source risks by minimizing the WEP in land-applied manures (e.g., Moore and Miller, 1994). Water-extractable P in manure is strongly tied to P in runoff when manures are broadcast and is used as a source variable of the P Index by some states (Elliott et al., 2006). The use of chemical amendments to lower P solubility is well established in wastewater treatment as well as in the treatment of ponds and lakes (Mason et al., 2005). Typically, metal salts are used that provide a metal cation to react with orthophosphate in solution to create an insoluble compound, either by adsorption or by precipitation or both. For instance, with livestock manures, alum has been shown to lower WEP in direct proportion to its amendment rate (Moore et al., 2000; Smith et al., 2001), primarily by adsorption of orthophosphate to secondary aluminum hydroxides (Shober et al., 2006). When alum-treated manures are broadcast on soils, losses of P in runoff from those soils can be less than 30% of those associated with untreated manure (Moore et al., 2000). Other compounds and materials have shown an ability to lessen P losses in runoff when applied to livestock manure, including aluminum sulfate, aluminum chloride, byproduct gypsum, coal fly ash, and wollastonite (Stout et al., 2000; Smith et al., 2001). Rare earth elements comprise the lanthanoid series and are a group of elements with periodic numbers ranging from 57 to 71. China represents the largest commercial source of REEs, with smaller amounts supplied by India, Brazil, and Russia (Hedrick, 2009). At high concentrations in the environment, REEs behave like other heavy metals in solution, and toxicity to plants and animals is a concern (Tyler, 2004). At very low concentrations,
A.R. Buda, C. Church, P.J.A. Kleinman, L.S. Saporito, and B.G. Moyer, USDA–ARS, Pasture Systems and Watershed Management Research Unit, University Park, PA, USA; L. Tao, Chinese Academy of Sciences, Beijing, China. Mention of trade names does not imply endorsement by the USDA. Assigned to Associate Editor Goswin Heckrath. Abbreviations: DRP, dissolved reactive phosphorus; ICP–EOS, inductively coupled plasma optical emission spectroscopy; PP, particulate phosphorus; REE, rare earth element; TP, total phosphorus; TS, total solids; WEP, water-extractable phosphorus.
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however, many studies have actually shown positive effects of REEs on plant biomass and growth (Tyler, 2004). Rare earth elements are used in a variety of applications, including as research tools in the environmental sciences and to benefit agricultural production, especially in East Asia. In oxide form, lanthanoid series REEs have been used to label soils in the investigation of erosional processes (e.g., Zhang et al., 2001; Matisoff et al., 2001; Polyakov and Nearing, 2004; Stevens and Quinton, 2008; Polyakov et al., 2009). In nitrate and chloride form, REEs are relatively soluble and have been used as a fertilizer source in China, with an estimated 16 to 20 million ha of land receiving REEs annually (Pang et al., 2001). The chemistry of REEs is well understood. Rare earth elements typically occur in nature as a 3+ charged cation with varying solubilities dependent on associated anions. In aqueous solutions, rare earth chlorides are very soluble, while phosphates and carbonates are insoluble (Firsching and Mohammadzadel, 1986; Firsching and Brune, 1991; Shaad et al., 1994). Due to their behavior, REEs have a strong potential to precipitate phosphate from solutions associated with soils and livestock manures. Indeed, the carbonate form of REEs has been proposed as an agent for P sorption from wastewaters (Kulperger et al., 2003). This study seeks to assess the potential for amending common livestock manures with REEs to control P loss in runoff and investigate the fate of REEs and P. Specifically, two REEs, lanthanum (La) and ytterbium (Yb), were mixed with poultry, swine, and dairy manures to quantify their ability to precipitate soluble P. A runoff experiment was conducted using packed soil boxes broadcast with manures to assess the fate of applied P and REEs.
Materials and Methods Manures and Soils Three manures were selected for the study to represent the broad range of livestock common to agriculture in the northeastern United States. Dairy manure and swine slurry were sampled from the Pennsylvania State University Dairy and Swine Centers, respectively, at University Park, PA. The dairy manure was from lactating Friesian dairy cows (Bos taurus) that was scraped from a free stall barn. Swine slurry was from finishing sows (Sus scrofa domestica L.) that was washed into a holding tank and agitated before sampling. Poultry manure was collected from a broiler chicken (Gallus gallus domesticus L.) operation in Princess Anne, MD, and was obtained from a litter storage shed where it served as a source of fertilizer for local fields. Surface samples of a Hagerstown soil (fine, mixed, semiactive, mesic Typic Hapludalf ) and a Honeoye soil (fine-loamy, mixed, active, mesic Glossic Hapludalf ) were collected from agricultural fields in New York and Pennsylvania. Hagerstown soils are derived from shale and sandstone residuum and are acidic, whereas Honeoye soils developed from calcareous glacial till and are alkaline. Soils were sieved to 1:1 molar ratio of REE to WEP), we inferred that the differences in DRP reduction efficiency between manures was primarily due to differences in manure properties. It is most likely that dry matter content of the manures (Table 2) determined the relative efficacy of REEs in reducing DRP concentrations by manure type. Dairy manure and swine slurry had very low dry matter content (72 and 15 g kg−1 respectively), whereas poultry litter had substantially higher dry matter content (560 g kg−1). Additions of REEs into liquid manures such as dairy and swine slurry likely allowed for more complete mixing of and, as a result, reaction between REEs and soluble manure P. In contrast, REEs that were applied directly to dry poultry litter had limited opportunity to mix 1032
and react with soluble P, except during the 30-min period of rainfall simulation. Therefore, application of REEs in liquid form would be more effective than application in dry form as has been observed with alum (Moore, 2004).
Fate of P and Applied La and Yb Fate in Runoff Water The fate of applied P and REEs in surface runoff varied somewhat for different treatments (Tables 3 and 4). In general, approximately 16 to 24% of applied P and 15 to 38% of applied REEs were exported in surface runoff. Rare earth element export in runoff from bare soil treatments was only about 3% of what was applied. Phosphorus and REE export in runoff from soils and manures amended with La and Yb primarily occurred in particulate form. In general, PP accounted for at least 90% of TP in runoff from bare soil, dairy manure, and swine slurry, whereas only 50% of TP in runoff from poultry was in particulate form. Greater than 98% of the REE load in runoff from soils and manures amended with La and Yb was in particulate form. As pointed out earlier, the addition of REEs to manures and soils suggested that a portion of DRP was converted to PP in surface runoff. To estimate the importance of this mechanism, we Journal of Environmental Quality • Volume 39 • May–June 2010
Table 4. Losses of P, total solids, and rare earth element in surface runoff.† Treatment
No manure No manure + La No manure + Yb Dairy manure Dairy manure + La Dairy manure + Yb Poultry manure Poultry manure + La Poultry manure + Yb Swine manure Swine manure + La Swine manure + Yb No manure No manure + La No manure + Yb Dairy manure Dairy manure + La Dairy manure + Yb Poultry manure Poultry manure + La Poultry manure + Yb Swine manure Swine manure + La Swine manure + Yb
TP
Phosphorus DRP
PP
Solids TS
TLa
Lanthanum DLa
PLa
TYb
Ytterbium DYb
PYb
————————————————————————————— mg ————————————————————————————— Hagerstown soil 1A 4A 6,000A 1B 0B 1B 0B 0B 0B 5A‡ A A A A A A A B B 7 1 6 6,000 46 1 45 3 0 3B A A A A B B B A A 6 1 6 6,000 1 0 1 41 1 41A A A A A B A B B B 156 44 112 17,000 0 0 0 1 0 1B A B A A A A A B B 116 8 109 19,000 1600 0 1599 0 0 0B A B A A B A B A A 109 8 101 17,000 3 0 3 897 1 895A A A A A B B B B B 162 109 53 7,000 1 0 1 0 0 0B A B A A A A A B B 124 64 60 7,000 187 1 186 0 0 0B A B A A B B B A A 115 59 56 7,000 0 0 0 189 3 185A A A A A B A B B A 84 29 55 8,000 0 0 0 1 0 1B A B A A A A A B A 103 4 99 8,000 545 0 544 1 0 1B A B A A B A B A A 130 4 126 11,000 4 0 4 1079 0 1078A Honeoye soil 6A 1A 5A 7,000A 1A 0A 1A 2B 0A 0B A A A A A A A B A 7 1 6 9,000 81 0 81 1 0 0B A A A A A A A A A 7 1 6 8,000 0 0 0 81 0 80A A A A A B A B B B 100 36 65 6,000 2 0 0 3 0 0B A B A A A A A B B 50 2 48 5,000 504 0 504 0 0 0B A B A A B A B A A 65 1 64 6,000 0 0 0 572 1 571A A A A A B B B A B 197 118 79 11,000 8 0 0 0 0 0A A B A A A A A A B 149 65 84 9,000 467 2 465 2 0 0A A B A A B B B A A 136 73 63 9,000 3 0 0 573 4 569A A A A A B A B A B 101 45 56 10,000 4 0 0 4 2 0A A B A A A A A A B 67 1 66 6,000 756 0 755 5 0 0A A B A A B A B A A 95 2 93 6,000 4 0 0 1306 0 1306A
† TP, total phosphorus; DRP, dissolved reactive phosphorus; PP, particulate phosphorus; TS, total solids; TLa, total lanthanum; DLa, dissolved lanthanum; PLa, particulate lanthanum; TYb, total ytterbium; DYb, dissolved ytterbium; PYb, particulate ytterbium. ‡ Letters indicate similar means as determined by Tukey’s pairwise comparison and apply to values within a given treatment.
assumed that declines in DRP with REE additions to manures indicated the amount of PP that was produced by precipitation reactions with REEs and that corresponding increases in PP indicated the amount of PP exported in runoff that was formally DRP (Table 4). The results of this exercise suggested that the percentage of PP export in surface runoff that was produced by precipitation reactions between DRP and REEs was approximately 0% for poultry litter, 6 to 11% for liquid dairy manure, and 55 to 100% for swine slurry. These results again pointed to the fact that wetter manures, particularly swine slurry, probably allowed for more complete reaction between soluble P and REEs and resulted in greater export of PP and particulate REEs in surface runoff. The importance of PP and particulate REE export in runoff from soils and manures amended with La and Yb also suggests that REEs may be useful in tracking manure constituents, including, but not limited to, PP, in runoff waters. Strong positive relationships were observed between PP and particulate REE concentrations in runoff across all treatments to which REEs were applied (Fig. 2). Under the conditions of the current experiment, molar concentrations of particulate REEs in surface runoff were roughly two times greater than those of PP. Based on available solubility product (Ksp) data for REEprecipitates with major anions, we can infer that REEs were most likely associated with phosphates (Log10 Ksp LaPO4 = −25.64; Log10 Ksp YbPO4 = −24.57; see Liu and Byrne, 1997) Buda et al.: Using Rare Earth Elements to Track Manure
as well as other manure constituents, especially carbonates (Log10 Ksp La2(CO3)3 = −29.91; Log10 Ksp Yb2(CO3)3 = −31.67; see Firsching and Mohammadzadel, 1986). Given the complex nature of manures and the possible reactions that could occur with REEs, more investigation into speciation of particulate rare earth fractions is warranted.
Fate in Soil Trends in WEP and REE concentrations at discrete soil depths (Fig. 3) illustrate the fate of applied P in soil and the effect of REEs in reducing the solubility of soil P. In bare soil with no applied REEs, WEP concentrations were similar across the three sampling depths. When manures were surface-applied, WEP concentrations were higher in the upper 1 cm of soil (Fig. 3). Concentrations of WEP in the surface 1 cm were particularly high in the swine slurry treatment, pointing to the translocation of P from the applied slurry into the soil and helping to explain the low DRP concentrations in runoff from this treatment relative to the other manures. When REEs were applied to soils and manures, WEP concentrations were lowest in the upper 1 cm, reflecting the precipitation of soil P by applied La and Yb, even in manure treatments (Fig. 3). In fact, trends in La and Yb concentrations for all treatments showed that the highest concentrations were found near the soil surface to which they were applied. The 1033
use in research settings as a manure labeling agent warrants further consideration. The surface application of REEs to manures had varied effects on P in runoff and soils when manures were land applied. In terms of DRP reductions in surface runoff, results show that surface applications of REEs to dry manures such as poultry litter are less effective than in liquid manures and slurries, which is likely due to mixing limitations. The most effective reductions of DRP in runoff by REEs were observed in the alkaline pH soil, although reductions of DRP in runoff from the acidic soil were still >50% under the experimental conditions of this study in which incidental transfers of P were maximized. Rare earth elements also showed a strong association with PP in runoff suggesting a potentially useful role in tracking the fate of P and other manure constituents from manure-amended soils. Finally, REEs that remained in the soil following runoff had a clear tendency to precipitate WEP, especially in soils receiving manure amendments.
References
Fig. 2. Relationship between particulate rare earth elements (μM L−1) and particulate P (PP; μM L−1) in surface runoff for (a) lanthanum and (b) ytterbium.
combined trends in WEP and REEs with depth in soil suggested that REE additions to soils and manures converted a portion of the available WEP to particulate REE-phosphates. A fraction of these compounds along with other REE precipitates (e.g., REE-carbonates) remained behind in the upper 1 cm of soil following the runoff event, as indicated by the high concentrations of REEs found at this soil depth (Fig. 3). While REE precipitates in shallow soil layers may be subject to transport in future runoff events, additional monitoring would be necessary to evaluate their long-term fate in soil (e.g., translocation, plant availability) and determine their impacts on plant and animal health.
Conclusions This study introduces a new use of REEs to reduce P losses from soils receiving manure, as well as to track the fate of P and REEs in surface runoff. Results show that REEs can be used at relatively low molar ratios with WEP to remove substantial amounts of P from manure. At approximately 1:10 ratios of La:WEP in dairy and poultry manure, P reduction ranged from 11 to 25%, whereas at La:WEP ratios closer to 1:1, P reduction improved to 95 to 98%. Given the costs of REEs ($40 to $450 kg−1) relative to other P binding amendments (e.g., alum at $0.52 kg−1 or lime at $0.08 kg−1), it is unlikely that REEs would be economically competitive; however, their
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