Variable sorghum growth in acid soils of subhumid West Africa

A sequence of experiments was conducted to define soil chemical properties associated with poor early growth of sorghum [Sorghum bicolor (L.) Moench] in selected Grossarenic and Plinthic Paleustalfs or Eutric Nitosols (FAO Legend) of subhumid West Africa. Millet [Pennisetum americanum (L.) K. Schum] appears to be tolerant to the soil problem under study. This soil constraint appears to inhibit sorghum growth and yield in all the soil positions of the toposequence of the Cinzana station (Mali), the toeslope excepted. Application of urea (100 mg N kg‐1 of soil) or liming followed by an N application neither prevented symptoms of poor growth nor significantly increased dry matter yield (DMY). However, application of P alone or any treatment combination containing P resulted in improved sorghum growth and yield. DMY was strongly correlated with Bray‐1 P (r = 0.74**). Exchangeable soil Al had a significant but negative impact on DMY (r = ‐0.42**). Amending the soil with Tilemsi rock phosphate (RP) or Diamou lime significantly increased exchangeable soil Ca 2+ and Mg 2+. Each of these amendments significantly reduced the concentrations of exchangeable soil Al3+. Phosphorus deficiency is one of the major factors limiting sorghum growth and yield in these Paleustalfs. The need for P is more critical than that of N in these soils. Aluminum toxicity is a secondary cause of this soil problem. An application as low as 2.5 mg P kg‐1 of soil not only prevented symptoms of poor early growth but produced a significant dry matter increase in the greenhouse. A Bray‐1 P level of 11.60 mg P kg‐1 of soil appears to be the critical P requirement for optimum sorghum growth in these Paleustalfs.