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RESEARCH ARTICLE

Metal bioavailability dynamics during a two-year trial using ryegrass (Lolium perenne L.) grown in soils treated with biosolids and metal salts

Amanda Black A E , Ronald G. McLaren A , Suzanne M. Reichman B , Thomas W. Speir C , Leo M. Condron A and Gary Houliston D
+ Author Affiliations
- Author Affiliations

A Department of Soil and Physical Sciences, Faculty of Agriculture and Life Sciences, Lincoln University, PO Box 84, Lincoln 7647, Christchurch, New Zealand.

B School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne 3001, Australia.

C Institute of Environmental Science and Research Ltd (ESR), PO Box 50348, Porirua 5240, New Zealand.

D Landcare Research, PO Box 40, Lincoln 7640, New Zealand.

E Corresponding author. Email: amanda.black@lincoln.ac.nz

Soil Research 50(4) 304-311 https://doi.org/10.1071/SR11315
Submitted: 29 November 2011  Accepted: 1 May 2012   Published: 28 June 2012

Abstract

A 24-month field lysimeter experiment using ryegrass (Lolium perenne L.) grown in three soil types was used to investigate metal bioavailability dynamics following amendment with biosolids and metal salts (Cd, Cu, Ni, Zn). Common surrogates of soil metal bioavailability (total soil metal, EDTA, Ca(NO3)2, total dissolved, diffusive gradient in thin film, and modelled free ion activity) were determined on soil samples taken every 6 months. Ryegrass was also harvested every 6 months and analysed for metal concentrations. Across soils and treatments dissolved organic carbon (DOC) and pH decreased, whereas dissolved Ca and Mg increased with time. The free ion activity concentrations of each metal also increased over 24 months, whereas Ca(NO3)2-extracted metals were unchanged. Zinc presented the most changes in bioavailability status, with total Zn concentration decreasing over time, and EDTA-extractable and soil solution Zn increasing significantly by 1.82 mg kg–1 (1.1%) and 1.52 mg L–1 (29%), respectively. Shoot concentration of Zn increased by 1.32 mg kg–1 (2.7%), whereas shoot Ni concentration decreased by 0.65 mg kg–1 (4%). The findings of this study clearly demonstrated that over 24 months, soil metal bioavailability and shoot metal concentrations register only minor changes and appear to be unaffected by soil DOC and pH fluctuations.

Additional keywords: bioavailability, biosolids, metals, ryegrass.


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