Modelling the soil water and salt balance of planted pastures irrigated with sodium sulphate rich mine effluent

Abstract

A field trial was established in January 2002 under a centre pivot at Syferfontein (Sasol) open cast mine, close to Secunda in the Mpumalanga Province (Republic of South Africa). Field measurements of crop, soil, water and weather were taken up till May 2003. Growth analyses were undertaken during the growing period of the planted pastures. Crop growth parameters and input parameters for long term predictions with the SWB model were also determined. The determinations were made for five planted pastures to evaluate if they could be irrigated with Na2SO4 rich mine effluent, and to see if the SWB model could reliably simulate crop growth, as well as the salt and water balance. The results indicated that Fescue (cv. Iewag), Lucerne, and Fescue (cv. Demeter) could be grown successfully with satisfactory yield and quality. No leaf burn was observed for the irrigated pastures. The ECe, pH and ESP of the soil increased slightly over the irrigation period, whereas the EC, pH and SAR of the soil solution fluctuated with rainfall. The model predicted the leaf area index (LAI), top dry matter (TDM), soil water deficit and salts reasonably well. In the long-term, 1420 mm year -1 of mine effluent can be used through irrigation. 93% of the salt added through irrigation was predicted to leach from the profile in a 20 year irrigation period which the rest precipitating in the 0.8 m deep soil profile in the form of gypsum. The Na2SO4 mine water can be utilized for pasture production provided that proper irrigation management and fertilization is done. Copyright 2004, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Beletse, YG 2004, Modelling the soil water and salt balance of planted pastures irrigated with sodium sulphate rich mine effluent, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-01182005-083427 / >