New Zealand Journal of Agricultural Research abstracts

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Adsorption of atrazine and phosphate as affected by soil depth in allophanic and non-allophanic soils

G. N. Magesan¹*
N. S. Bolan²
R. Lee¹

¹Landcare Research
Private Bag 3127
Hamilton, New Zealand
email: gujja.magesan@forestresearch.co.nz

²Institute of Natural Resources
Massey University
P.O. Box 11 222
Palmerston North, New Zealand

*Present address: Forest Research, Private Bag 3020, Rotorua, New Zealand.

Abstract  Quantification of soil processes, such as adsorption, is needed for predicting the fate of agricultural chemicals in soils. Adsorption is affected by soil properties, which vary with depth. We conducted a laboratory study to determine the influence of soil depth on the adsorption of an organic solute (atrazine) in both allophanic and non-allophanic soils, and an inorganic solute (phosphate) in two non-allophanic soils. Adsorption isotherms of atrazine and phosphate were determined using ¹⁴C-labelled atrazine and KH₂PO₄, respectively, in batch equilibrium. The adsorption isotherms for atrazine were almost linear, and adequately described by the Freundlich equation. For phosphate the adsorption isotherms exhibited substantially more curvature and were best described by the Langmuir equation for one of the soils. Generally, adsorption of both solutes decreased with depth. While atrazine adsorption appeared related to such factors as percentage clay content, total C, cation exchange capacity (CEC), and surface area, no similar relationships appeared apparent for phosphate adsorption.

Keywords  adsorption; atrazine; Freundlich equation; Langmuir equation; phosphate

A01043 Received 13 December 2002: accepted 14 March 2003; published 30 June 2003
New Zealand Journal of Agricultural Research, 2003, Vol. 46: 155-163
0028-8233/03/4602-0155 $7.00/0 © The Royal Society of New Zealand 2003

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