Unacidulated and partially acidulated Phosphate Rock as P sources in an acid Ultisol in the forest zone of southeastern Nigeria

Abstract

AbstractThe relative agronomic effectiveness (RAE) of phosphate rock (PR) and its 50% partially acidulatet form (PAPR) (less soluble P sources) relative to single superphosphate (SSP) and diammonium phosphate (DAP) (soluble sources) was studied in a two year field trial with maize in an acid Ultisol in the forest zone of southeastern Nigeria.All the P sources increased top growth, grain, and stover yields over the control. The RAE of PR relative to SSP was lower in the first year (25 and 38% for dry matter (DM) and grain yield (GY) respectively) compared to the second (64 and 58% for DM and GY respectively). Partial acidulation increased the yields by 17 and 7% for DM and GY, respectively, in the first year but not in the second. The RAE of PR and PAPR relative to DAP followed the same trend.The response curves of DM, and GY to rates of applied P showed that lower grain yields were produced in the first compared to the second year. The soluble and less soluble sources built up the Bray 1 extractable P to levels adequate for maize production in the agroecological zone.