In the natural environment, soil pH has an enormous influence on soil biogeochemical processes. Soil pH is, therefore, described as the “master soil variable” that influences myriads of soil biological, chemical, and physical properties and processes that affect plant growth and biomass yield. This paper discusses how soil pH affects processes that are interlinked with the biological, geological, and chemical aspects of the soil environment as well as how these processes, through anthropogenic interventions, induce changes in soil pH. Unlike traditional discussions on the various causes of soil pH, particularly soil acidification, this paper focuses on relationships and effects as far as soil biogeochemistry is concerned. Firstly, the effects of soil pH on substance availability, mobility, and soil biological processes are discussed followed by the biogenic regulation of soil pH. It is concluded that soil pH can broadly be applied in two broad areas, i.e., nutrient cycling and plant nutrition and soil remediation (bioremediation and physicochemical remediation).

Yam is an important food and cash crop in West Africa (the yam belt) whose production is traditionally nonsedentary due to its substantial nutrient demand. Population growth, urbanization, and existing soil degradation have made nonsedentary farming virtually impossible. Despite the numerous research invested in yam production within and outside the yam belt, some gaps remain to be filled owing to changing climate events and global developments. Alarmingly, the yam belt is facing sharp yield declines despite increasing production areas. The key edaphic and ecological drivers of yam production in the global yam belt were reviewed. The implications for yam production were discussed along with prospects for future research, sustainable production, and soil management. The main findings are that (1) agroecological zone, postplanting cultural practices, and climate change and variability ecological drivers, while (2) tillage, soil type, texture, and fertility were the edaphic factors. The most critical among the drivers, principally, soil fertility, entails the biological and chemical through which nutrients are released lude, and physical soil fertility which enhances low bulk density, porosity, and water retention for free yam tuber expansion. Soil fertility was the most cited driver, which explains why yam is often the first crop in the cropland cultivation cycle in the yam belt. Data show that yam yields decline with time under native fertility and mineral fertilizer application due to the voracious nutrient extraction by tubers. Conversely, yields increase chronologically under organic fertilizer application due to the additive effects of the latter on soil properties. Thus, a yam fertilizer program to develop specific yam fertilizer formulations and the adoption of the Terra Preta Model are proposed to sustain future yam production.

Background: Application of biochar has been suggested as a carbon (C) management strategy to sequester C and enhance soil quality. An incubation study was carried out to investigate the interactive effect of biochar and cattle manure application on mineralization of carbon (C) in a tropical coastal savanna sandy soil. Methods: The soils were amended with three sole levels of cattle manure (0, 13 and 26 tons ha −1) or biochar (0, 20 and 40 tons ha −1) and four combined manure-biochar levels (20 or 40 tons ha −1 biochar plus 13 or 26 tons ha −1 manure) and CO 2 evolution was measured over 56 days incubation period. The soils were analyzed for mineral N (NH 4 +-N and NO 3 −-N) and water extractable organic C, and net N mineralization, and priming effect (PE) values calculated. Results: The cumulative C mineralized increased in the sole manure and biochar amended soils, resulting in 45-125% positive PE. However, co-application of biochar and manure decelerated decomposition of C, probably through adsorption of labile C and net N immobilization, subsequently leading up to negative 35% PE. Conclusions: The results suggest that co-application of biochar and cattle manure can potentially stabilize C in manure amended sandy soils, albeit with a temporary mineral N limitation to plants.

Understanding the dynamics of agricultural expansion, their drivers, and interactions is critical for biodiversity conservation, ecosystem-services provision, and the future sustainability of agricultural development in Sub-Saharan Africa (SSA). However, there is limited understanding of the drivers of agricultural expansion. A systematic review of the drivers of agricultural expansion was conducted from 1970 to 2020 using Web of Science, Elsevier Scopus and Google Scholar. Two researchers reviewed the papers separately based on inclusion and exclusion criteria. Fifteen papers were included in the final systematic review. The paper proposed expansion pathways in a conceptual framework and identified proximate and underlying drivers. Population dynamics and government policies were found to be key underlying drivers of agricultural expansion. The proximate drivers include economic opportunities such as agriculture mechanisation and cash crops production, and more troubling trends such as soil fertility decline and climate change and variability. This paper further explores the constraints that have been found to slow down agricultural expansion, including strong land institutions and good governance.

Background: Ample quantities of ashes generated from domestic biomass energy combustion in Ghanaian kitchens are currently disposed of despite their potential agricultural value. This study aimed to investigate the potential agricultural value of charcoal and firewood ashes in terms of differences in the chemical and mineralogical compositions, and to identify the suitability of aqua regia, H 2 SO 4 , vinegar and distilled water to extract plant nutrients (Ca, Mg, K, Na, and P). The chemical compositions were determined by atomic absorption spectrometry after extractions with aqua regia, H 2 SO 4 , vinegar and distilled water while mineralogy was determined by X-ray powder diffraction. Results: The charcoal ash had 0.2 units, 13 ds m −1 , and 7% higher (P < 0.05) pH, EC, and CCE, respectively, than the firewood ash, whereas the latter had 6, 17, 43, and 139 µg g −1 higher (P < 0.05) As, Cu, Mg, and Zn contents, respectively, and more minerals with 86% being Mg-rich. Calcite and calcium oxide were the dominant minerals occurring in both ashes followed by calcium manganate (CaMnO 3). Aqua regia and vinegar were suitable for Ca, acidic solutions for Mg, H 2 SO 4 and aqua regia for P with Na and K being virtually soluble in all solutions. Lead, Mn, Ni, and Zn had values in the order of hundreds. Conclusions: Although the ashes differ, they both contain trace elements whose bioavailability may differ and may not necessarily lead to plant uptake after field application. This offers an opportunity for further research into the threshold trace element contents of wood ash and their relationship with plant uptake in different soil pH and soil types.