Phosphorus is an important primary nutrient required by plants in large quantities. The various forms of P that plants can take up are the primary monobasic phosphate ion (H₂PO₄^-), secondary dibasic phosphate ion (HPO₄^2-) and phosphate ion (PO₄^3-). In tropical soils, phosphorus adsorption is a major process that controls its availability to crops. Soils with low phosphorus adsorption capacity are often unable to supply adequate phosphorus to the growing crops thereby affecting their yields. This paper reviews the phosphorus adsorption phenomenon in a tropical soil. The review showed that Langmuir isotherm, Freundlich isotherm, Brunauer-Emmett-Teller (BET) isotherm, Dubinin-Radushkevich, and Temkin isotherm are the mostly used isotherms models for describing phosphorus adsorption. From the review, soil acidity and alkalinity, soil temperature and the electrical potential of clay surface are the main factors influencing phosphorus adsorption. Also, precipitation was discovered to be the main mechanism of P adsorption in tropical soils. Fertilization practices such as the addition of organic manure, crop residues, rock phosphate, water-soluble P fertilizers and incorporation of phosphorus solubilizing organism are highly recommended to increase P solubility and availability in highly weathered soil.

Introduction: Biochar is one of the commonly used soil amendments for sustainable agriculture. The effect of biochar on crop yields depends on the quality of the biochar, which is influenced by feedstock type and pyrolysis conditions. Sole application of pineapple waste biochar and compost, and their combination has not been rigorously investigated. In this study, we investigated the effects of pineapple waste biochar and compost applied solely or in combination on growth and yield of pineapple on a coastal savanna Acrisol in Ghana.Methods: The split-plot design with three replications was used, with pineapple varieties as the main plot and fertilizer application rates as the sub-plots.Results and discussion: The results showed that sole application of biochar and compost or their combination as a soil amendment increased pineapple growth and yield as compared to the unamended soil. Biochar applied in combination with compost/or inorganic NPK (nitrogen, phosphorus, and potassium) fertilizer significantly increased plant height and the number of leaves of pineapple plant, which resulted in improved fruits yield of the three (sugar loaf, MD2 and smooth cayenne) pineapple varieties at maturity over control, sole application of biochar, compost and inorganic NPK fertilizer. The Smooth cayenne variety outperformed MD2 and Sugar loaf variety.Conclusion: In conclusion, the results revealed that biochar applied solely or in addition to compost or inorganic NPK fertilizer has the capability to enhance soil quality and improve pineapple yield. Application of biochar in combination with compost/or inorganic NPK improves pineapple growth and yield.

Potentially toxic metals in soils are a threat to food security and harmful to human because it enters the food chain through crop uptake. Hence, it is critical to know the levels of potentially toxic metals in soils due to agricultural land use patterns and how they can be removed from the soil. This review discussed the effect of different land-use patterns on heavy metal accumulation, their removal using biochar. A desktop review which employed PRISMA was used to put together information from peer-reviewed papers including journal articles, books, thesis and reports. It was shown that potentially toxic metals mainly found in the soil include; As, Cu, Cd, Zn, Cr, Co, Ni, Sb, Hg, Th, Pb, Si, and Se. The sources of these potentially toxic metals accumulation in soils were organic and inorganic fertilizer application, irrigation, pesticides and weedicides application and atmospheric deposition. However, different land-use patterns (greenhouse field, vegetable field soils, forest field, and maize field soil) had a significant accumulation of heavy metals (Cr, Ni, Cu, As, Cd, and Zn) due to increasing crop yield through the application of fertilizers and pesticides. Biochar was found to be effective in the removal of 18 to 40% of these potentially toxic metals from the soil. The mechanisms of removal were; precipitation, physical sorption, complexation, and ion exchange and electrostatic interaction. It can be concluded that biochar applied solely or in addition to compost has strong stability to remove heavy metals accumulated in soils due to land use patterns.