The domestic requirement for wheat in South Africa is approximately 2.8 million tons and annually the shortfall on local production is imported to meet the demand. During the past 25 years two distinct wheat marketing mechanisms characterised the wheat industry, impacting significantly on both research and industry. In 1996 the single channel marketing system through the Wheat Board made way for a liberal marketing environment in which market forces of supply and demand determine price. This refocused most research activities on factors to lower input costs and risks, while increasing the profitability of wheat production. Significant challenges were experienced with much stricter milling and baking quality requirements impacting on not only the development of adapted wheat cultivars for South African conditions, but also on fertiliser and cultivar recommendations, as well as production practices. Minimum tillage, preharvest sprouting, as well as the threat of Russian wheat aphid and stripe rust were some of the pertinent challenges faced during this time. Significant scientific breakthroughs of international importance were made with regard to the physiological and biochemical nature of insect resistance and plant defence as well as the transfer of resistance genes from alien species. This review provides an overview of the most pertinent wheat research undertaken from 1983 to 2008.

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Standard triaxial compression tests were carried out on an agricultural sandy loam soil to assess the effect of soil dry bulk density and moisture content on soil mechanical properties, namely, cohesion, internal friction angle, Young's modulus of elasticity and Poisson's ratio. Regression analyses were performed to establish mathematical relationships for simulating the variation in these mechanical properties as a function of dry bulk density and moisture content. These relationships were developed for six typical field moisture contents ranging from 3 to 22% d.b., and various dry bulk density levels ranging from 1Á15 to 1Á82 Mg m À3. Results showed that all mechanical properties increased with dry bulk density, except the internal friction angle that was an independent property. Cohesion, Young's modulus of elasticity and Poisson's ratio decreased with moisture content, except that the Poisson's ratio increased after the moisture content exceeded 17% d.b. However, the internal friction angle was also independent of moisture content. The regression equations developed to relate the soil cohesion, Young's modulus of elasticity and Poisson's ratio with moisture content and dry bulk density were quite simple, and had high determination coefficients ranging from 0Á92 to 0Á96. The regression equations indicated that the three mechanical properties varied linearly with moisture content and non-linearly with dry bulk density. Quadratic relationships were detected for the variations in properties studied and dry bulk density. These equations may be used for prediction of the variation in the mechanical properties (except internal friction angle) of sandy loam soils for any combination of moisture content and dry bulk density. Establishing these equations can be considered an advantage from an economical point of view because of avoiding the need of carrying out the costly triaxial compression test. #

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