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Influence of long-term wheat residue management on soil
fertility indicators of an Avalon soil at Bethlehem
P.F. Loke 1 , E. Kotzé 2 , C.C. du Preez 3
1. Department of Soil, Crop and Climate Sciences, University of the Free State, P.O. Box 339, Bloemfontein,
Republic of South Africa, lokepf@yahoo.com
2. 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
3. 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
Awareness of the environmental aspects of soil quality and crop production has been increasing in recent years,
which has led to renewed interest in crop residues as a source of soil organic matter (SOM) and nutrients. Some
residue management practices have been examined since 1979 in a long-term wheat trial at the ARC-Small Grain
Institute near Bethlehem on an Avalon soil. This trial provides thus an excellent opportunity to evaluate the longterm
effects of residue management on some soil fertility indicators and hence wheat response. The treatments that
were applied are: straw disposal (burned and unburned), tillage (ploughing, stubble mulch and no-tillage) and weed
control (chemical and mechanical). Soil samples were collected every 10 years at depth intervals of 0-50, 50-100,
100-150, 150-250, 250-350 and 350-450 mm, and analysed for various soil fertility indicators. In 1999 tillage
influenced SOM more than straw burning or weeding method, particularly in the upper 100 mm soil. No- and
mulch tillage, especially when combined with chemical weeding increased SOM more than when ploughing was
combined with mechanical weeding. Soil acidification was suppressed by burning and a combination of mulch or
no-tillage with chemical weeding. P, K, Cu, Fe, Mn and Zn were higher in the burned plots than in unburned. This
was also true for no- and mulch tillage in the upper 150 mm soil compared to ploughing. Grain yield did not
correspond with the higher organic matter and pH resulting from mulch and no-tillage. This could be attributed to
low availability of nutrients in the upper 150 mm soil. The 30 year measurements confirm to a large extent the
results of 1999.
KEYWORDS: nutrients, organic matter, soil acidity, straw disposal, tillage
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