Soil amendments play a critical role in improving soil health and supporting sustainable crop production, especially under declining soil fertility and climate-related stress. However, their impact varies because each amendment influences the soil through different biogeochemical processes rather than a single universal mechanism. This review synthesizes current knowledge on a wide range of soil amendments, including compost, biosolids, green and animal manure, biochar, hydrochar, bagasse, humic substances, algae extracts, chitosan, and newer engineered options such as metal–organic framework (MOF) composites, highlighting their underlying principles, modes of action, and contributions to soil function, crop productivity, and soil carbon dynamics. Across the literature, three main themes emerge: improvement of soil physicochemical properties, enhancement of nutrient cycling and nutrient-use efficiency, and reinforcement of plant resilience to biotic and abiotic stresses. Organic nutrient-based amendments mainly enrich the soil and build organic matter, influencing soil carbon inputs and short- to medium-term increases in soil organic carbon stocks. Biochar, hydrochar, and related materials act mainly as soil conditioners that improve structure, water retention, and soil function. Biostimulant-type amendments, such as algae extracts and chitosan, influence plant physiological responses and stress tolerance. Humic substances exhibit multifunctional effects at the soil–root interface, contributing to improved nutrient efficiency and, in some systems, enhanced carbon retention. The review highlights that no single amendment is universally superior, with outcomes governed by soil–crop context. Its novelty lies in its mechanism-based, cross-amendment synthesis that frames both yield and carbon outcomes as context-dependent rather than universally transferable. Within this framework, humic substances and carbon-rich materials show potential for climate-smart soil management, but long-term carbon sequestration effects remain uncertain and context-dependent.

The cation exchange capacity (CEC) of three benchmark soils in the rain forest region of Southwestern Nigeria, were measured by three standard CEC methods. Results obtained were compared with a view to selecting the best suited CEC method for the soils. The study sites were the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, and Itagunmodi settlement. Two representative soil profile pits each were established in soils developed in coarse-grained granite and gneiss, fine-grained biotite gneiss and schist, and the amphibolite. The three methods gave different CEC values in the order of CEC-pH 8.2 > CEC-pH 7 > ECEC. There was a significant correlation between soil organic matter (SOM) and the CEC obtained by each of the three methods (P ≤ 0.05), meanwhile, total clay showed no significant correlation. ECEC provided the best estimate of the CEC for the soils and adequate SOM management is crucial to enhance sustainable productivity of the soils.

Topography significantly influences soil development and characteristics within an uneven agricultural field. Therefore, a comprehensive understanding of soil attributes and processes through detailed pedological knowledge is crucial for effective soil management. This research was carried out in Wasinmi, southwestern Nigeria, to delineate and categorise the soils across different slopes for agricultural insights. Three soil profiles were excavated across the topographical sequence, specifically designated as upper, middle, and lower slope positions. The prevailing soil texture was sandy loam with a discernible trend of lighter soil colour as the slope descended and soil depth increased. The pH of the soil ranged from moderately acidic to slightly acidic. The saturated hydraulic conductivity and soil organic matter content were lowest on the lower slope. Available phosphorus distribution varied inconsistently with higher concentrations of heavy minerals observed at the upper slope. The study underscored the influential role of topography in soil property variations and the need for tailored management practices. The classification of the soils revealed Typic Plintustults in the upper and middle slope positions, while the soils in the lower slope were identified as Typic Kandiaquults. This study demonstrated that topography significantly influenced soil properties, thereby emphasising the need for informed practices to better support the long-term sustainability of land use and agricultural outputs in topographically diverse landscapes.

The study examined the composition and forms of iron and aluminium oxides in benchmark soils of central southwestern Nigeria. Soils developed from distinct parent rock types, including coarse-grained granite and gneiss, fine grained biotite gneiss and schist, and the amphibolite complex which correspond to the parent rocks of the soils of Iwo (Typic Paleustults), Egbeda (Rhodic Kandiustults) and Itagunmodi (Typic Haplustults) Associations, respectively, were selected for the study. Notably, these soils collectively encompass approximately 60% of the total land area in central southwestern Nigeria. The less than 2 mm soil fractions were pre-treated with hydrogen peroxide to remove soil organic matter. Thereafter, oxides of Fe and Al were extracted using three different extractants: dithionite-citrate-bicarbonate (DCB) mixtures, acidified ammonium oxalate and sodium pyrophosphate solution. The quantification of Fe and Al oxides contents in the respective extracts were carried out using Inductively Coupled Plasma – Atomic Emission Spectrometry. The research findings indicated that the DCB extractable forms of Fe and Al oxides were more abundant compared to other forms of these oxides, and a substantial portion of these oxides within the soils existed in crystalline form. Among the soil series studied, Itagunmodi series exhibited the highest amount of DCB- and oxalate extractable Fe oxides, while Iwo series had the highest content of Fe and Al oxides extracted by sodium pyrophosphate solution. Importantly, the presence of Fe oxides were found to negatively impact the reactivity of SOM in the soils.

This study investigated the contributions of soil organic matter (SOM), clay, and various forms of Fe and Al oxides to the cation exchange capacity (CEC) of highly weathered tropical soils in central southwestern Nigeria. Soils representing major types in the region—Typic Paleustults, Rhodic Kandiustults, and Typic Haplustults—were sampled by genetic horizon. SOM was removed using hydrogen peroxide, and parallel subsamples underwent selective extractions targeting crystalline (dithionite–citrate–bicarbonate), poorly crystalline (acid ammonium oxalate), and organically complexed (sodium pyrophosphate) Fe and Al oxides. Changes in CEC following each treatment were used to assess the functional roles of the removed components. SOM removal resulted in substantial reductions in CEC across all soils, accounting for 38%–47% of total CEC in surface horizons, confirming SOM as the dominant source of exchangeable charge. Removal of oxides produced variable responses depending on the form and soil depth. In many subsurface horizons, CEC increased, indicating that these oxides often mask clay exchange sites. Conversely, decreases in CEC observed in some surface horizons indicate that oxides can also contribute pH‐dependent charge or stabilize organic functional groups. Clay fractions exhibited modest intrinsic CEC, consistent with kaolinitic mineral dominance. These findings demonstrate that CEC in these highly weathered tropical soils is controlled primarily by SOM and the degree to which Fe and Al oxides regulate access to clay exchange sites. Enhancing organic matter and managing oxide‐induced masking are therefore key strategies for improving nutrient retention and soil fertility in tropical agroecosystems.