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

Abstract

The relative agronomic effectiveness (KAE) of phosphatc rwh II'KI and its SO 5% partially acidulatct forni (PAPR) tless soluble P sources) rclative to singlc supcrphospliate (SSP) and diamnionium phosphate (DAI') (soluble sources) was studied in a two year field trial with mni7c in an acid Ultisol in the forest zone of southeastern Nigeria.All the P sources incrcascd top growth. grain. wid stover yields over the control. The KAE of PR relative to SSP was lower in the first yeiir (25 and 38 4 for dry niatter (DM) and grain yicld (GY) respcciivcly) compand io the second (64 and SX ' 6 for DM and GY rcspcctivcly). 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 aid PAPK relative to DAP followed the same trend.The responx curves of DM. and GY to rates of applied IJ showed thui lower grain yields were produced in the first compared 10 the sccond y a r . l h c soluble and Ic olublc sources built itp the Bray I cxtrdctable P lo levcls adcquatc for maizc production in ihe agriwcological zone.