South Africa - Inkaba.org

Effect of long-term residue management on organic matter in a
Plinthosol cropped annually with wheat
E. Kotzé 1 , C.C. du Preez 2
1. Department of Soil, Crop and Climate Sciences, University of the Free State, P.O. Box 339, Bloemfontein,
Republic of South Africa, kotzee@ufs.ac.za
2. Department of Soil, Crop and Climate Sciences, University of the Free State, P.O. Box 339, Bloemfontein,
Republic of South Africa, dpreezcc@ufs.ac.za
ABSTRACT
Understanding the role of organic matter in maintaining a healthy soil is essential for developing ecologically
sound agricultural practices. A long-term trial at the ARC-Small Grain Institute near Bethlehem in the Eastern
Free State, South Africa offered the oppurtunity to establish the role of various agricultural practices on some soil
fertility indicators in a Plinthosol, and to establish whether differences in wheat grain yield could be attributed to
changes in the fertility indicators. The trial has been running since 1979 and the treatments that were applied are
two methods of straw disposal (burned and unburned) x three methods of tillage (ploughing, stubble mulch and no
tillage) x two methods of weed control (mechanical and chemical). Soil samples were collected at various depth
intervals every 10 years since the trial has commenced in 1979, and various fertility indicators were then analyzed
and compared. Organic C and total N were used as indices of organic matter. The different tillage practices had a
larger effect on organic matter than either straw burning or weeding method, especially in the upper 100 mm soil.
No tillage and to a lesser extent mulch tillage, especially when combined with chemical weeding were more
beneficial to soil organic matter than when ploughing was combined with mechanical weeding. The combination
of no tillage and chemical weeding is therefore recommended to maintain and even increase the organic matter
content of this Plinthosol when cropped annually with wheat. The response of soil enzymes to organic matter
changes as a result of residue management is being investigated now.
KEYWORDS: organic matter, plant nutrients, straw disposal, tillage practices, weed control methods.
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