AGRONOMIC EVALUATION OF FERTILIZER PRODUCTS DERIVED FROM SUKULU HILLSPHOSPHATE ROCK

Partial acidulation of phosphate rock (PR) or compaction of PR with so luble P fertilizers can improve the usefulness of unreactive PR for us e as P fertilizer. A greenhouse study was conducted to evaluate noncon ventional phosphate fertilizers derived from a low reactive Sukulu Hil ls PR from Uganda. Raw PR (which contained 341.0 g kg(-1) Fe2O3), bene ficiated or concentrate PR, partially acidulated PR (PAPR) and PR comp acted with triple superphosphate (TSP) were evaluated. Compacted mater ials had a P ratio of PR:TSP = 50:50. PAPR materials were made by 50% acidulation with H2SO4 TSP was used as a reference fertilizer. Fertili zers were applied to an acidic (pH = 5.4) Hiwassee loam (clayey, kaoli nitic, thermic Rhodic Kanhapludults) at rates of 0, 50, 100, 200, 300 and 400 mg P kg(-1) soil. Two successive corn (Zea mays L.) crops were grown for 6 weeks. Compacted concentrate PR + TSP and raw PR + TSP we re 94.4 and 89.7% as effective as TSP, respectively, in increasing dry -matter yields for the first corn crop. PAPR from the concentrate was 54.8% as effective as TSP. Raw PR, concentrate PR and the PAPR from th e raw PR were ineffective in increasing dry-matter yields. The same tr ends were obtained when P uptake was used to compare effectiveness. In effectiveness of the raw PR and its corresponding PAPR was attributed to a high Fe2O3 content in the raw PR. Bray I and Pi paper were found to be nearly equally suitable at estimating available P in the soils t reated with responsive fertilizer materials. Mehlich 1 overestimated a vailable P in soil treated with raw PR, concentrate PR or the PAPR fro m the raw PR.