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The rising cost of lime, traditionally used to address soil acidity and its detrimental effects on soil fertility, has prompted the exploration of organic by-products as more affordable alternatives for mitigating soil acidity, particularly for low-income farmers. Therefore, the objective of this study was to investigate effects of filter cake (FC) and bagasse ash (BA) application on soil acidity under greenhouse condition. The experiment was laid out in a completely randomised design with four replications. The FC and BA were investigated separately each with six levels (0, 20, 40, 60, 80, and 100) t/ha-1. The acidic soil was collected from Imdibir area at a depth of 0-20 cm, air dried, ground and passed through 4 mm sieve. Each pot was received 4 kg of soil with respective treatment material after they were well homogenised. The laboratory analysis revealed that the soil had an initial pH of 5.1, while filter cake and bagasse ash had pH values of 8.0 and 10.2, respectively. Application of FC increased soil pH from 5.1 to 7.3, along with improvements in organic matter, nitrogen, phosphorus, sulphur, potassium, calcium, magnesium, and cation exchange capacity. Similarly, BA application raised pH from 5.1 to 7.4 and enhanced organic matter, nitrogen, phosphorus, sulphur, potassium, calcium, magnesium, and cation exchange capacity. The maximum effects for both FC and BA occurred at the highest application rate (100 t/ha-1), while iron and manganese content increased with BA application but decreased as rates increased, and copper and zinc levels were positively affected by both FC and BA applications. Overall, both FC and BA applications significantly improved soil pH and nutrient content. The findings of this study can provide practical and cost-effective solutions for improving soil fertility and crop production [ABSTRACT FROM AUTHOR]

Peat soils are frequently analysed using the same standard methods and extractants as for mineral soils, despite the distinctive nature of organic soils. The extractants used are well-suited for peat soils of near-neutral pH but it is still unclear whether they are suitable for acidic tropical peat soils. The study reported here compared the effectiveness of three standard reagents in extracting potassium, calcium, and magnesium from tropical peat of different degrees of decomposition, collected from three field locations in peninsular Malaysia. Three basic cations (K+, Ca2+ and Mg2+) were extracted using Mehlich 1, NH4OAc (ammonium acetate) buffered at pH 7 and NH4OAc at pH 4. The results showed that raising the pH of the extractant reduced the amounts of K+, Ca2+ and Mg2+ extracted. The average amounts extracted by Mehlich 1 and NH4OAc at pH 4 were frequently significantly higher than the amounts extracted by NH4OAc at pH 7, in most of the peat types sampled regardless of location. Compared with the extraction using NH4OAc at pH 7, the extractions with Mehlich 1 and NH4OAc at pH 4 are likely to provide closer estimations of these basic cations, because the pH of the extractants reflects the true pH of tropical peat soils.

Peat soils are frequently analysed using the same standard methods and extractants as for mineral soils, despite the distinctive nature of organic soils. The extractants used are well-suited for peat soils of near-neutral pH but it is still unclear whether they are suitable for acidic tropical peat soils. The study reported here compared the effectiveness of three standard reagents in extracting potassium, calcium, and magnesium from tropical peat of different degrees of decomposition, collected from three field locations in peninsular Malaysia. Three basic cations (K+, Ca2+ and Mg2+) were extracted using Mehlich 1, NH4OAc (ammonium acetate) buffered at pH 7 and NH4OAc at pH 4. The results showed that raising the pH of the extractant reduced the amounts of K+, Ca2+ and Mg2+ extracted. The average amounts extracted by Mehlich 1 and NH4OAc at pH 4 were frequently significantly higher than the amounts extracted by NH4OAc at pH 7, in most of the peat types sampled regardless of location. Compared with the extraction using NH4OAc at pH 7, the extractions with Mehlich 1 and NH4OAc at pH 4 are likely to provide closer estimations of these basic cations, because the pH of the extractants reflects the true pH of tropical peat soils. [ABSTRACT FROM AUTHOR]

Compostos orgânicos hidrossolúveis de resíduos vegetais depositados na superfície do solo podem melhorar a fertilidade do subsolo, pela neutralização da acidez e transporte de Ca e Mg. Com o objetivo de avaliar o efeito dos compostos orgânicos hidrossolúveis de materiais vegetais nos atributos químicos de um Latossolo Vermelho distroférrico, foi desenvolvido um experimento no Instituto Agronômico do Paraná (IAPAR), Londrina, com amostras de solo acondicionadas em colunas nas quais se aplicaram os tratamentos: água destilada, calcário incorporado na camada 0-5 cm de profundidade, calcário e percolação com extratos de nabo forrageiro, aveia preta, palha de trigo, milho e soja. No extrato percolado, foram determinados os teores de ligantes orgânicos hidrossolúveis (LOH) por potenciometria com eletrodo seletivo de Cu2+; ácidos orgânicos tituláveis (AOT) por titulação ácido-base e ânions orgânicos (AO) pela soma de bases. As concentrações de AO e AOT variaram de 7,0 a 32,0 mmol L-1 e de LOH de 0,60 a 2,23 mmol L-1. Todos os extratos vegetais aumentaram o pH, os teores de Ca, Mg e K trocável e diminuíram a acidez potencial e o Al trocável até 15 cm de profundidade, enquanto o efeito da calagem sem extrato foi observado somente até 10 cm de profundidade. A concentração de compostos orgânicos solúveis oriundos dos materiais vegetais correlacionou-se com o pH, Al trocável, H+Al e V % do solo na camada de 0-20 cm, confirmando a participação destes na melhoria dos atributos químicos do solo e ação da calagem superficial quando o material vegetal está presente.The water-soluble organic compounds of plant residues released on the soil surface can improve the subsoil fertility, due to the neutralization of acidity and Ca and Mg transport. An experiment was conducted at the Instituto Agronomico do Parana (IAPAR), Londrina, to evaluate the effect of water-soluble organic compounds of plant extracts on the chemical characteristics of a dark Red Latosol (Typic Haplortox), on soil samples in columns. The treatments consisted of: distilled water, lime incorporated in the 0-5 cm soil layer, lime and percolation of the following plant extracts: oilseed radish, black oat and wheat, maize and soybean straw. The following properties were determined in the plant extracts: the water-soluble organic ligand (WSOL) by potentiometry with selective Cu2+ electrode; titration of organic anions (TOA) and organic anions (OA) by base addition. The OA and TOA concentrations varied from 7.0 to 32.0 mmol L-1 and WSOL from 0.60 to 2.23 mmol L-1. All plant extracts increased pH and exchangeable Ca, Mg and K and decreased the potential acidity and exchangeable Al down to a soil depth of 15 cm, while the effect of lime without plant extract was only observed down to 10 cm. The soluble organic compound concentrations of the plant residues were correlated with pH, Al3+, H+Al and soil base saturation in the 0-20 cm layer, confirming the role of these organic compounds to improve the chemical characteristics of an acid soil as well as the action of the surface-applied lime.

Soil acidification in managed ecosystems such as agricultural lands principally results from the increased releasing of protons (H+) from the transformation reactions of carbon (C), nitrogen (N) and sulphur (S) containing compounds. The incorporation of liming materials can neutralize the protons released, hence reducing soil acidity and its adverse impacts to the soil environment, food security, and human health. Biochar derived from organic residues is becoming a source of carbon input to soil and provides multifunctional values. Biochar can be alkaline in nature, with the level of alkalinity dependent upon the feedstock and processing conditions. This review covers the fundamental aspects of soil acidification and of the use of biochar to address constraints related to acidic soil. Biochar is increasingly considered as an effective soil amendment for reducing soil acidity owing to its liming potential, thereby enhancing soil fertility and productivity in acid soils. The ameliorant effect on acid soils is mainly because of the dissolution of carbonates, (hydro)-oxides of the ash fraction of biochar and potential use by microorganisms. [Display omitted] • In managed ecosystem, soil acidification results mainly from the carbon and nutrient cycling. • Acidification is a major soil constraint impacting soil health and heavy metal toxicity. • The level of alkalinity in biochar depends on the feedstock and processing conditions. • Biochar liming value is derived from carbonates, and hydro-oxides of the ash fraction. • Biochar ameliorates acid soils by suppling base cations and reducing aluminium toxicity. [ABSTRACT FROM AUTHOR]