Amelioration of Soil Acidity in Ferralsols of Central Uganda

Soil acidity is one of the major constraints limiting crop productivity in Central Uganda. Thus, the ideal soil pH for crop production ranges from 5.5 to 6.8, but in Central Uganda, crops are believed to be cultivated in soils with pH below these ranges. Given the adverse effects of soil acidity to agricultural production, appropriate measures such as the use of lime could be an option to improve the productive capacity. Henceforward, soils were sampled from farmers’ fields in Mpigi, Mubende and Wakiso Districts representing Central Uganda to evaluate rates of CaCO3 and corncob biochar in a greenhouse incubation study. Afterwards, 2 kg of soil was weighed, placed in a plastic container and thoroughly mixed with 0, 1, 3 and 5 g equivalent to 0, 1, 3 and 5 tons/ha CaCO3 and corncob biochar. Soils were arranged in a Complete Randomized Design (CRD) and moistened with 500 ml of water to bring it to about field capacity and pH determination done for a period of three (3) months until equilibration. The analysis of variance (ANOVA) showed significant effect (P<0.001) on soil pH when CaCO3 and corncob biochar were applied with the three districts recording a near neutral pH of 6.7.

After pH equilibration in the greenhouse, rates of CaCO3 and corncob biochar that raised the soil pH in each medium were used to calculate the lime rates i.e., 0, 120, 360 and 600 g applied in the fields. In a Complete Randomized Design (CRD) consisting of four replications, soybean varieties were applied as the main plots while rates of CaCO3 and corncob biochar were applied as the sub plots. The analysis of variance (ANOVA) showed that CaCO3 had significant effect (p<0.001) on soil pH with Mpigi recording the highest soil pH (6.7) followed by Mubende (pH 6.6). Rates of CaCO3 and corncob biochar also showed significant effect (p<0.001) on soybean grain yield compared to 0 g CaCO3 and corncob biochar. Application of 600 g of corncob biochar showed significant effect (p<0.001) on soil pH in the different study locations. Besides, increased in CaCO3 rate to 600 g recorded the highest (7137.5 kg ha-1) soybean grain yield in Wakiso District while 600 g of corncob biochar recorded the highest (5637.5 kg ha-1) soybean grain yield in Mpigi District thus signifying the potential effect of CaCO3 and corncob biochar in Acid Ferralsols.