Abstract

The subject of this chapter is soil chemistry. The chapter is entitled Processes and Factors Affecting Phosphorus (P) Adsorption in Soils. The chapter aims to give an overview of the major mechanisms responsible for phosphate sorption (i.e., adsorption and absorption of phosphate) in soils, particularly of acid soils. According to studies conducted by some soil scientists, the major soil factors affecting P sorption are time, soil pH, soil organic matter, and iron and aluminium oxides of soils. Studies conducted indicated that adsorption of the P increases as the P ages in the soil. Soil pH affects phosphate adsorption but the effect is limited for adsorption by soils in the pH range of 4–8. Organic matter may affect P adsorption in two ways: indirectly by inhibiting iron oxide crystallisation and directly by competing for adsorption sites. On per mole basis, oxalate extractable aluminium oxides adsorb nearly twice as much P as oxalate extractable iron oxides due to poorer crystallinity (higher specific area) of the aluminium oxides compared to the iron oxides and also to a higher charge of the former. The chapter also highlights the pedotransfer functions (PTFs) of Borggaard, which can be used to calculate for the P adsorption in highly weathered acid soils.

Highlights

  • With increasing demand of agricultural production and as the peak in global production will occur in the decades, phosphorus (P) is receiving more attention as a non-renewable resource [1, 2]

  • Phosphate saturation is the proportion of adsorption sites occupied by phosphate, which is normally taken as the ratio between adsorbed phosphate and the phosphate adsorption capacity (PAC) of the soil [13]

  • Borggaard [24] found that most Feox:Fedcb ratios were rather high in some Danish sandy soils, the correlation between Feox:Fedcb and organic matter was not significant which suggests that there is no inhibition of adsorption sites for phosphate

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Summary

Introduction

With increasing demand of agricultural production and as the peak in global production will occur in the decades, phosphorus (P) is receiving more attention as a non-renewable resource [1, 2]. In many agricultural systems in which the application of P to the soil is necessary to ensure plant productivity, the recovery of applied P by crop plants in a growing season is very low, because in the soil more than 80% of the P becomes immobile and unavailable for plant uptake because of adsorption, precipitation, or conversion to the organic form [3]. All of this means, that P can be a major limiting factor for plant growth. Phosphate saturation is the proportion of adsorption sites occupied by phosphate, which is normally taken as the ratio between adsorbed phosphate and the phosphate adsorption capacity (PAC) of the soil [13]

Specific adsorption of phosphorus by aluminium and iron oxides
Factors affecting phosphate adsorption in soils
Soil pH
Organic matter
Phosphate sorption as a function of the iron and aluminium oxides of soils
Adsorption isotherms
Phosphorus sorption isotherms and equations
Langmuir equation
Temkin equation
Pedotransfer functions (PTFs) for estimation of phosphate adsorption capacity
Predictability of the PTF of Borggaard et al
Findings
Conclusion

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