Effect of the form of agricultural lime on neutralizing soil acidity and soya beans (glycine max l.) yield on two Zambian alfisols

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Chiwele, Lewis
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Soil acidity is a common constraint to crop production in Zambia. Agricultural lime is applied in dry powder form to acid soils to neutralize acidity. New liming materials in aqueous suspension form have recently been introduced on the Zambian market and their effectiveness in neutralizing acidity has not been tested. A study was conducted to assess whether the form in which lime is applied to soil affects its effectiveness in neutralizing acidity and its effect on Soya bean yield. Two strongly acid Alfisols, Choma and Chakunkula Soil Series with pH values of 4.02 and 4.32; exchangeable Al3+ levels of 0.26 and 0.15 cmol (+)/kg and Al saturation levels of 19 % and 9.5 % , respectively were used as test soils. Four liming materials comprising 3 dry powder forms and one in aqueous suspension were acquired and their neutralizing values were determined. Aqueous suspensions were also made for each dry powder material, to give 4 aqueous samples and 3 dry powder samples for testing. Lime requirements of the two soils were calculated using the formular 2 x exch Al3+ as the lime requirement. The lime requirements were 850 and 500 kgCaCO3/ha for Choma and Chakunkula Soil Series, respectively. Three kilograms of disaggregated soil were mixed with the 7 lime materials corresponding to the lime requirement for each soil. They were kept moist in plastic pots at room temperature for 12 weeks. Soil pH and exchangeable acidity were measured weekly in the first 5 weeks and fortnightly thereafter. The effect of the form of liming material on Soya bean yield was determined in field trials on the two soils. A Randomized Complete Block Design with eight treatments which comprised of 7 lime materials and a control without lime. Powder lime was broadcast on each plot and incorporated into the soil using hand hoes. Aqueous suspensions were prepared by mixing the mass of dry lime required per plot with 8 litres of water and applying them onto the plots using watering cans. Soya bean, was planted in rows 45cm apart after applying Compound D fertilizer ( 10: 20:10) at a rate of 200 kg/ha. Upon maturity, the crop was harvested and the grain yield was measured and recorded. The results showed that lime in aqueous suspension was more effective in raising soil pH than lime in dry powder form on both soils. It took less time to raise the soil pH to 5.5 with lime in aqueous suspension than with lime in dry form on both soils. On Choma soil, lime in aqueous suspension was more effective than lime in powder form in reducing exchangeable acidity. No significant difference was observed in the effectiveness of the two forms of lime in reducing exchangeable acidity on Chakunkula soil series. No significant differences in Soya bean yield were observed between plots treated with lime in aqueous suspension and those with lime in dry powder form at both sites. A greater increase in Soya bean grain yield was observed in limed plots on Choma soil series which had an initial Al saturation of 19 % than on Chakunkula soils which had an initial Al saturation of 9.5 %. Yield increases of 43 % for lime in aqueous suspension and 27 % for lime in dry powder form were obtained on Choma Soil Series while increases of 4 % and 17 % were obtained on Chakunkula soil series. This study demonstrated potential advantages of applying agricultural lime in aqueous suspension compared to applying it in dry powder form but more investigations are needed. Key words: Liming, pH, Exchangeable acidity, Lime formulation, Soya beans, Yield
Soya beans , Lime formulation , Soil acidity