Critical pH and exchangeable Al of four acidic soils derived from different parent materials for maize crops

The purpose of this study is to determine the critical soil pH, exchangeable aluminum (Al), and Al saturation of the soils derived from different parent materials for maize. An Alfisol derived from loess deposit and three Ultisols derived from Quaternary red earth, granite, and Tertiary red sandstone were used for pot experiment in greenhouse. Ca(OH)(2) and Al-2(SO4)(3) were used to adjust soil pH to target values. The critical soil pH was obtained by two intersected linear lines of maize height, chlorophyll content, and yield of shoot and root dry matter changing with soil pH. In low soil pH, Al toxicity significantly decreased plant height, chlorophyll content, and shoot and root dry matter yields of maize crops. The critical values of soil pH, exchangeable Al, and Al saturation varied with soil types. Critical soil pH was 4.46, 4.73, 4.77, and 5.07 for the Alfisol derived from loess deposit and the Ultisol derived from Quaternary red earth, granite, and Tertiary red sandstone, respectively. Critical soil exchangeable Al was 2.74, 1.99, 1.93, and 1.04 cmol(c)kg(-1) for the corresponding soils, respectively. Critical Al saturation was 5.63, 12.51, 14.84, and 15.16% for the corresponding soils. Greater soil cation exchange capacity and exchangeable base cations led to lower critical soil pH and higher critical soil exchangeable Al and Al saturation for maize.