CSIRO Publishing blank image blank image blank image blank imageBooksblank image blank image blank image blank imageJournalsblank image blank image blank image blank imageAbout Usblank image blank image blank image blank imageShopping Cartblank image blank image blank image You are here: Journals > Soil Research   
Soil Research
Journal Banner
  Soil, land care and environmental research
blank image Search
blank image blank image
blank image
  Advanced Search

Journal Home
About the Journal
Editorial Structure
For Advertisers
Online Early
Current Issue
Just Accepted
All Issues
Special Issues
Sample Issue
For Authors
General Information
Submit Article
Author Instructions
Open Access
For Referees
Referee Guidelines
Review an Article
Annual Referee Index
For Subscribers
Subscription Prices
Customer Service
Print Publication Dates
Library Recommendation

blue arrow e-Alerts
blank image
Subscribe to our Email Alert or RSS feeds for the latest journal papers.

red arrow Connect with us
blank image
facebook twitter logo LinkedIn

Now Online

Land Resources Surveys


Article << Previous     |         Contents Vol 47(1)

Positive charge discovered across Western Australian wheatbelt soils challenges key soil and nitrogen management assumptions

M. T. F. Wong A B, K. Wittwer A

A CSIRO, Private Bag 5, Wembley, WA 6913, Australia.
B Corresponding author. Email: mike.wong@csiro.au
PDF (309 KB) $25
 Export Citation


Nitrogen management in Western Australia (WA) and in cropping areas elsewhere in Australia assumes that soil contains negligible or no positive charge and is therefore unable to retain nitrate against leaching. The amount of water needed to displace nitrate is thus assumed to be the drainable volume of water held by the soil (1 pore volume), and in sandy soils about 100 mm drainage is assumed to be required to displace nitrate by 1 m. The clay mineralogy of the highly weathered soils of the WA wheatbelt is dominated by kaolinite and iron and aluminium oxides. This mineralogy suggests likely occurrence of positive charge and anion exchange capacity (AEC), since these minerals can carry positive charge under normal acidic field situations. We measured AEC of soils sampled widely across the WA wheatbelt by independent leaching and batch equilibration methods of charge measurement. This showed widespread occurrence of positive charge and AEC in these soils. AEC ranged from 0 to 2.47 mmolc/kg and is linearly correlated with the potassium chloride or monocalcium phosphate extractable sulfate content of the soil. This correlation provides a rapid screening method to identify soils with positive charge. Application of ion-chromatographic theory showed that AEC has a large effect in delaying nitrate leaching by up to 12.5 pore volumes. The most highly charged soil (2.47 mmolc/kg) thus needed 12.5 times more water to displace nitrate than currently assumed. This potentially large delay in nitrate leaching affects the optimum amount and time of fertiliser application, rates of soil acidification attributed to nitrate leaching and the benefit of ameliorating subsoils to allow roots access to subsoil water and leached nitrate. It also calls into question the use of anions such as bromide to trace water flow and estimate recharge in these soils.

Keywords: anion exchange capacity, AEC, leaching delay, nitrate adsorption, pore volume, variable charge, charge : sulphate ratio.

Subscriber Login

Legal & Privacy | Contact Us | Help


© CSIRO 1996-2016