Abstract
Potassium (K) is a macronutrient required by plants for energy production, enzyme activation, formation of cell wall, production of protein, and photosynthesis. However, K in the soil solution is leached from the rhizosphere before it interacts with soil colloids because of the abundance of kaolinite clay minerals in mineral acid soils such as Ultisols and Oxisols. These soils are highly weathered, low in organic matter, low in pH, but high aluminium (Al), and iron (Fe) ions. As a result, K becomes unavailable for plants, and this affects crop production and farmers’ profitability. This problem has steered the attention to the application of amendments to minimise K loss. Animal manures, plant residues, and composts applications are some of the corrective measures taken to improve the K availability in tropical acid soils. However, there is dearth of information on co-application of charcoal and wood ash as soil amendments to improve the K availability and the changes they cause to the dynamic equilibrium of K in mineral acid soils. Hence, this review discusses the dynamics, availability of K, and proposed mechanisms involved when charcoal and wood ash are used to amend tropical acid soils. The optimisation and understanding of the role of charcoal and wood ash co-application as soil amendments have potential benefits to improve the K availability and physicochemical properties of mineral acid soils.
Highlights
The efficacy of chemical potassic fertilizers in nourishing plant needs are often compromised because most of the nutrients from fertilizers are commonly lost via leaching
Weathered soils are high in Al3+ and Fe2+ because of their low pH [1,2]. These ions are adsorbed onto the soil exchange complexes through replacement of H+. This cation exchange causes the release of H+ ions into the soil solution
The leaching of soil solution K can increase the release of K from soil minerals [109], but the induction of this replenishment mechanism depends on the soil pH, movement of K in soils, soil cation exchange capacity (CEC), liming, and rate of K uptake by plants and microbes [35,87]
Summary
The efficacy of chemical potassic fertilizers in nourishing plant needs are often compromised because most of the nutrients from fertilizers are commonly lost via leaching. There is evidence on organic amendments’ capability in increasing the nutrient availability [9,10,11,12], there is dearth of information on improving the K availability of mineral tropical acid soils using charcoal and wood ash. It is hypothesised that the combined use of potassic fertilizers, charcoal, and wood ash in tropical acid soils could improve the K availability because of their acid, Al3+, and Fe2+ neutralizing effects. The objectives of this review were to (i) discuss the dynamics and availability of K in tropical acid soils and (ii) propose possible mechanisms involved when charcoal and wood ash used to amend potassic fertilisers in tropical mineral acid soils
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