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Phosphorus-Quenching in Soils under Tropical Climates
Published in Mark Anglin Harris, Confronting Global Climate Change, 2019
In most soils, phosphorus solubility and availability occurs only within a narrow range of pH values. Thus at high or neutral pH, phosphate reacts with calcium to form minerals, such as apatite. Under acidic conditions, phosphorus may react with aluminum and iron to form minerals, such as strengite and variscite (USDA 2018). Whereas optimum pH for phosphorus availability is 6.5, additives can be used to keep the soil pH around that level. As each soil is different, measurements on random samples can reveal the general pH level of the soil.
Aluminum
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Global Resources and Universal Processes, 2020
Bernhard Wehr Johannes, Cardell Blamey Frederick Paxton, Martin Kopittke Peter, William Menzies Neal
The leading cause of poor fertility of acidic soils is Al toxicity (Asher, Grundon, and Menzies 2002, Horst, Wang, and Eticha 2010, Poschenrieder et al. 2008). Toxicity of Al in plants is mainly manifested by an inhibition of root growth, with Al3+ and Al13 considered the most toxic species (Kinraide 1991, 1997, Poschenrieder et al. 2008, Singh et al. 2017). The action of Al on plant cells is both in the apoplast (binding to cell wall components) (Kopittke et al. 2015) and in the cytoplasma (formation of reactive oxygen species and oxidative stress responses (Yamamoto et al. 2003, Singh et al. 2017)). The correlation between Al concentration and root grow inhibition is sometimes poor. This is due to the several Al-hydroxy species that coexist within a narrow pH band and cannot be investigated in isolation. Furthermore, the activities of individual species must be calculated from equilibrium data that may be uncertain (Boudot et al. 1996). The critical Al concentration at which root elongation is inhibited is as low as 0.1–0.5 mg/L (5–20 μM) in solutions of low ionic strength, representative of acid soils. Exact critical values depend on the plant species and the conditions in which the plants are grown. Generally, root hairs are more sensitive to Al toxicity than roots (Brady et al. 1993). Root growth inhibition results in short stubby roots and absence of root hairs, leading to poor water and nutrient utilization by plants. The main site affected by Al is near the elongation zone of roots (1–4 mm behind the root tip) (Blamey, Nishizawa, and Yoshimura 2004, Sivaguru and Horst 1998, Kopittke et al. 2015). The reaction of aluminum with phosphate anions in the soil may result in the precipitation of Al-phosphate minerals (e.g., variscite), lowering phosphorus availability to plants. This effect is accentuated by the lower phosphorus uptake capacity of Al-damaged roots.
Kinetics of the precipitation reaction between aluminium and contaminant orthophosphate ions
Published in Environmental Technology, 2023
Ivan Ricardo de Barros, Cristina Benincá, Everton Fernando Zanoelo
It is valuable to observe that in both the kinetic experiments considered, the pH rapidly dropped to approximately 2.5 in a similar fashion (Figures 6d and 7b). This confirms that in both these cases the consumptions of Al3+ and to form AlPO4(s) by reaction 8 in Table 4 caused the consumption of the other reactant aluminium species and orthophosphates in general (Figure 7(d)). Such a behaviour is explained by the hydrolysis reactions 1–7 in Table 4, which were also responsible for the removal of protons from water molecules and, consequently by the decrease in pH as time evolved. Such a variation of pH with time during which aluminium phosphate (indeed, AlPO4·2H2O(s) or variscite) precipitates has been documented in the literature [25].
Enrichment of primary macronutrients in biochar for sustainable agriculture: A review
Published in Critical Reviews in Environmental Science and Technology, 2022
Adnan Asad Karim, Manish Kumar, Ekta Singh, Aman Kumar, Sunil Kumar, Arati Ray, Nabin Kumar Dhal
Transformation of P in biochars derived from peanut husk, wheat and maize straw through slow pyrolysis (300–600 °C) was studied by Xu, Zhang, Shao, and Sun (2016). Water-soluble P forms are dominant in biochars produced at low temperature (up to 400 °C), which are transformed into more labile form (400 to 600 °C) and ultimately to stable form with increasing pyrolysis temperature (600 to 800 °C). During pyrolysis, above 200 °C organic P (ortho-monoester) fractions changed into inorganic forms (Ortho and Pyro-phosphate). Sodium pyro-phosphate (Na4P2O7) and monetite (CaHPO4) were major species present in biochars, whose proportions increased with pyrolysis temperature. The other stable minor forms of P in biochars as detected by Solid state 31P NMR are Crandallite (CaAl3(OH)5(PO4)2), Wavellite (Al3(OH)3(PO4)2·5H2O), Hydroxyapatite [Ca5(PO4)3OH], Sodium pyro-phosphates [Na2H2P2O7], Tri-sodium di-phosphate [Na3HP2O7], Senegalite [Al2(OH)3(PO4)·H2O], Variscite (AlPO4·2H2O), Di-calcium phosphate dihydrate (CaHPO4·2H2O).