Grondversuring en bekalking van Oos-Vrystaatse gronde onder droëlandkoring

English: The value of liming of agricultural land has been demonstrated all over the world during the past century. Therefore liming as an agro-economical practice has been adopted widely by farmers with a beneficial impact on sustainable crop production for future generations. However, soil acidity is still a common yield limiting factor for a variety of crops in the Free State, Mpumalanga, KwaZulu-Natal and parts of the Western Cape. Due to above mentioned reasons incubation and field experiments were conducted over several years to quantify the following after liming of various Eastern Free State soils. Firstly, the changes in soil acidity parameters and secondly, the growth and development of wheat cultivars that differ in tolerance to aluminium (AI). Over time liming increased the pH(KCI) and decreased the percentage acid saturation (%AS) significantly in the top- (0-200mm) and subsoil (200-400mm) of all the localities. In the topsoils a good correlation was obtained between pH(KCI) and %AS. An increase in pH(KCI) of 0.1 will more or less be concomitant with a decrease of 5.5 in %AS. The amount of lime needed to raise the pH(KCI) or to lower the %AS up to a specific level, differed between the localities because of buffer capacity. Since pH(KCI) showed a better correlation with lime than %AS, it was decide to use pH(KCI) as parameter to develop a model with which the lime requirement of a soil can be calculated: Y=8.3240X1-O.0459X2-1.0370, where Y=lime requirement (ton ha"), X1=~pH(KCI and X2=clay content (%) At all localities the good AI-tolerant cultivar gave significant higher yields than the medium and poor AI-tolerant cultivars. When no lime was applied on the unlimed soils the good AI-tolerant cultivar produced economical yields, which was not the case with the medium and paar AI-tolerant cultivars. The medium and poor Al-tolerant cultivars responded therefore very well to liming with yield increases up to 90%. The good, medium and poor Al-tolerant cultivars showed a yield decrease of 15% at an %AS of 30, 10 and 8, respectively. Considering that %AS correlated better with yield than pH(KCI), liming to the required %AS of a cultivar is a possibility. Differences in AI-tolerance between cultivars resulted in that the optimum economic lime levels differ between cultivars. The optimum lime level of the cultivar with good AI-tolerance was the lowest, followed by the medium and paar AI-tolerant cultivars. Liming of acid soil has become an expensive practice for farmers, which led to the adoption of planting AI-tolerant cultivars to bridge the soil acidity problem. During this process soils has slowly started to deteriorate with an accompanying lost of yield and income per hectare. The results of this study clearly indicate the economical value of liming acid soils for wheat production.