VARIABLE SORGHUM GROWTH IN ACID SOILS OF SUBHUMID WEST-AFRICA

A sequence of experiments was conducted to define soil chemical proper ties associated with poor early growth of sorghum [Sorghum bicolor (L. ) Moench] in selected Grossarenic and Plinthic Paleustalfs or Eutric N itosols (FAO Legend) of subhumid West Africa. Millet [Pennisetum ameri canum (L.) K. Schum] appears to be tolerant to the soil problem under study. This soil constraint appears to inhibit sorghum growth and yiel d 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 symptom s of poor growth nor significantly increased dry matter yield (DMY). H owever, application of P alone or any treatment combination containing P resulted in improved sorghum growth and yield. DMY was strongly cor related with Bray-1 P (r = 0.74*). Exchangeable soil Al had a signifi cant but negative impact on DMY (r = -0.42*). Amending the soil with Tilemsi rock phosphate (RP) or Diamou lime significantly increased exc hangeable soil Ca2+ and Mg2+. Each of these amendments significantly r educed the concentrations of exchangeable soil Al3+. Phosphorus defici ency 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 t hese soils. Aluminum toxicity is a secondary cause of this soil proble m. An application as low as 2.5 mg P kg-1 of soil not only prevented s ymptoms of poor early growth but produced a significant dry matter inc rease in the greenhouse. A Bray-1 P level of 11.60 mg P kg-1 of soil a ppears to be the critical P requirement for optimum sorghum growth in these Paleustalfs.