Assessment of Soil Acidity Constraints on Soybean Production in Cross River State, South South Nigeria

This study assesses soil acidity constraints on soybean production in Cross River State, located in Nigeria's South South geopolitical zone. Soybean is an important legume and cash crop in Cross River State, but its production is severely limited by strongly acidic soils where aluminium toxicity reduces root growth, nodulation efficiency, and grain yield. Using a descriptive field design, soil samples were collected from 30 soybean-producing farms in Obubra, Etung, and Abi local government areas, and analysed for pH in water and CaCl2, exchangeable aluminium, active and exchangeable acidity, organic carbon, and total nitrogen. Simultaneously, root nodule counts, nodule weight, and soybean shoot dry weight were measured on plants at 45 days after planting on the same farms. Correlation and regression analyses were conducted to relate soil acidity parameters to nodulation and plant growth indicators. Findings revealed that 87 percent of sampled soils had pH below 5.0 and exchangeable aluminium above 1.0 cmolc/kg. Significant negative correlations were found between exchangeable aluminium and both nodule number (r = -0.79) and shoot dry weight (r = -0.82), confirming the central role of aluminium toxicity in limiting biological nitrogen fixation and crop performance. Aluminium-tolerant soybean varieties were available to fewer than 10 percent of surveyed farmers. The study recommends the use of aluminium-tolerant soybean varieties, liming at moderate rates, and inoculation with effective Bradyrhizobium strains as the most accessible integrated solutions for soybean acid soil constraints in Cross River State. Keywords: soil acidity, soybean, aluminium toxicity, Cross River State, nodulation.