Liming and Lime-Phosphorus-Zinc Interactions in Two Nigerian Ultisols: II. Effects on Maize Root and Shoot Growth

Two greenhouse experiments, the first a complete factorial comprising six rates of lime, four of phosphorus (P) and three of zinc (Zn) on two kaolinitic Ultisols, and the second involving factorial combinations of lime at four levels or gypsum at two chemically equivalent levels with three levels of P on one Ultisol, examined lime-nutrient interactions in the growth of maize (Zea mays L.) shoots and roots in relation to interactions in nutrient availability in the soil. Strong, highly significant interactions in maize growth were observed on both soils. The lime-P interaction was positive and occurred only at lime rates less than equivalent to the KCl-exchangeable Al content. Both total P uptake and root surface area per unit length increased substantially with liming to pH 5.5, but P uptake per unit root surface area was not altered. Total P uptake was linearly correlated with root surface area at each level of applied P and with the product of root surface area and available P, suggesting that the lime-P interaction was due primarily to the effect of lime on improving root exploitation of available P in the soil. The third-order lime × P × Zn interaction was observed at high lime rates in the pH range of 6 to 7. Overliming depressed yields only where Zn was not applied; shoot yields were closely related to Zn activities in soil solution. total P uptake was not reduced by liming soils to neutrality but total Zn uptake was linearly correlated with the product of Zn activity (controlled by soil pH) and root weight (influenced by P nutrition). Aluminum toxicity was shown to be the primary growth-limiting factor for maize grown in the two Ultisols under greenhouse conditions. Plants did not respond to gypsum treatments even though tissue concentrations and gross uptake rates of Ca were raised to levels comparable to equivalent lime treatments. Maize shoot yields were closely related to exchangeable Al saturation and total Al concentration in soil solution and declined at levels in excess of 28% and 4 µg/ml, respectively. Maximum shoot yields occurred at comparatively low rates of lime sufficient to raise soil pH to about 5.0 in the fertilized soils.