Screening groundnut (Arachis hypogaea L.) genotypes for tolerance to soil acidity.
Shezi, Ntandoyenkosi Happiness.
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Groundnuts (Arachis hypogaea L.) are an important subsistence and cash crop for smallholder farmers in Southern Africa. They require well drained light textured soils. However, most light textured soils are acidic and inherently infertile, and therefore require supplementary nutrients and amelioration with lime. In addition to application of a basal fertilizer, groundnut production also requires Ca. This increases the inputs required to produce the crop, particularly for smallholder farmers. The study examined two options for smallholder farmers, outside the classical lime application, for ameliorating soil acidity, i.e., evaluating the response of different groundnut genotypes for tolerance to soil acidity and low-cost liming alternatives. Initially ten groundnuts genotypes were screened for tolerance to soil acidity. Following this, three genotypes classified as tolerant and susceptible were used to evaluate the effect of high acid saturation on germination, emergence and seedling establishment. Thereafter, selected cultivars were used to compare calcium silicate, as an alternative to dolomitic lime, for ameliorating soil acidity and supplying calcium to developing pods. All three studies were conducted under controlled conditions: 25 ± 5°C and 20 ± 3°C day/night temperatures, 65% RH. Results measured as plant height, leaf area, yield, concentration and uptake of selected macro-and micro-nutrients showed that different groundnut genotypes differed in their response to soil acidity. Genotypes like Billy, Selmani, Rambo and JL 24 had low Al uptake and high Ca and P uptake and were classified as tolerant to acidity. In addition, these genotypes also had a higher leaf area and high number of nodules compared with Anel, Harts, Sellie, RG 784 and Robbie. With the exception of JL 24 all other tolerant genotypes (Billy, Selmani and Rambo) were large seeded. In the early establishment stage especially, root development was susceptible to soil acidity, but Rambo appeared to perform better than Jasper and Harts. Calcium silicate reduced soil acid saturation and provided enough calcium for pod development, suggesting that it may be used as an additional source of calcium. Soil acidity increased grain protein concentration and reduced its oil content, however, amelioration with either lime source reversed this trend. Thus, growing groundnuts in acid soils has implications for the commercial value of the product in terms of oil or protein supply. Overall, the study suggests that a combination of application of a cheap liming source like calcium silicate and growing tolerant cultivars, like Rambo, Billy and JL 24 might provide a window of opportunity for smallholder farmers to produce groundnuts possibly with only a fraction of the costs associated with ameliorating soil acidity.