DOI: https://doi.org/10.36347/sajb.2026.v14i04.001

Pages: 264-270

This study was carried out in Côte d'Ivoire, where acid rice soils are characterized by chronic phosphorus (P) deficiency and low chemical fertility that constrain productivity. The use of Morocco rock phosphate (RP) as an alternative amendment to triple superphosphate (TSP), represents a promising option; however, its medium-term effects on soil chemical properties across contrasting rice-growing ecologies remain insufficiently documented. The present study assessed the residual effects of six PR/TSP combinations (ranging from 100% RP to 100% TSP at a total application rate of 300 kg ha⁻¹) on soil chemical properties after two successive cropping cycles in lowland (hydromorphic sandy soils, pH 5.6) and upland (argilo-sandy Ferralsols, pH 5.2) ecologies in the Man zone, Côte d'Ivoire. A randomized complete block design with four replicates and eight treatments was used. Before establishment, both soils showed degraded chemical characteristics: very low available phosphorus (P intial: 5 mg kg⁻¹ in upland, 2.1 mg kg⁻¹ in lowland), low CEC (8.5 and 3.4 cmol⁺ kg⁻¹ respectively) and low organic carbon. After two cycles, results show that phosphate amendment significantly increased total nitrogen, available phosphorus, organic matter and cation exchange capacity (CEC) in both ecologies. In lowland, CEC reached 116.75 cmol⁺ kg⁻¹ under T0 at the second cycle, and organic matter increased strongly (up to 92,269 mg kg⁻¹ under T6). Treatment T3 (80% PR + 20% TSP) showed the highest available P content in lowland (14 mg kg⁻¹) and upland (2 mg kg⁻¹). The C/N ratio revealed rapid mineralization under T4 in lowland (C/N = 6.4 at cycle 2), while the upland showed normal to slow mineralization (C/N between 11 and 13). Lowland ecology responds more strongly to phosphate amendment, due to more intense biological activity and favorable redox conditions. These results confirm the importance of differentiated phosphate fertilization management according to rice ecologies.