Understanding phosphate sorption characteristics of mineral amendments in relation to stabilising high legacy P calcareous soil. (June 2020)

• Record Type: Journal Article
• Authors: Fan, Bingqian; Ding, Jiahui; Fenton, Owen; Daly, Karen; Chen, Qing
• Is Part Of: Environmental pollution. Volume 261(2020)
• Publication Date: 2020-06
• Subjects: Phosphorus legacy soil -- Alum -- Dolomite -- Stabilisation -- Sorption-desorption; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2020.114175
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: In China, excessive phosphorus (P) application in protected vegetable fields has led to high legacy P stores. Soil amendment with alum or dolomite is one of many best management practices (BMPs) used to reduce P losses in calcareous soils. However, both the kinetics and mechanisms of P sorption and soil available P in amended soils are understudied. Herein, both aspects were looked at under controlled conditions. Firstly, a sorption study which coupled P concentrations with poorly-crystalline Al hydroxides and dolomite was conducted. Results from this batch experiment showed that P sorption on poorly-crystalline Al hydroxides was homogenous and occurred mainly via displacement of inner-sphere hydroxyl (Al–OH) instead of the formation of AlPO4 . However, the amount of sorbed P reached maximum sorption of 73.1 mg g −1 and did not change with further increase in P concentration. It was observed that P adsorbed onto the dolomite surface at low P concentrations, whereas hydroxyl replacement and uneven cluster precipitation of Ca3 (PO4 )2 occurred at high P concentrations. A second 90 day incubation experiment investigated changes to soil available P and sorption-desorption across variable rates of amendments (0–50 g kg −1 ). Results showed that alum amendment at a rate of 50 g kg −1 decreased soil CaCl2 –P and Olsen-P concentrations by 91.9% and 57.8%, respectively. However, Olsen-P increased when the dolomite rates were <20 g kg −1 . Phosphorus sorption-desorption of the amended soil showed alum had higher P sorption efficiency than dolomite at low addition rates (<10 g kg −1 ). However, soil amended with high dolomite rates (>10 g kg −1 ) could sorb more P in comparison with alum when P concentrations were increased. The P status of the amended soil was closely connected to the P sorption mechanisms on mineral amendments, soil P concentrations and soil properties. Graphical abstract: Image 1 Highlights: P sorption on poorly-crystalline Al hydroxides was mainly through displacement of inner-sphere Al–OH groups. Higher alum rates and P concentrations contributed to the inner-sphere P sorption. Mg in dolomite inhibited the formation of hydroxylapatite (HAP) at higher P concentrations. Dolomite addition decreased soil CaCl2 –P, but increased Olsen-P. Abstract : In the present study, it was found that phosphate was mainly sorbed as inner-sphere complexes rather than a formation of AlPO4 on poorly-crystalline Al hydroxides at pH 6.5. When alum was added to soil, it was shown that higher rates of alum added and higher P concentrations facilitated easier formation of inner-sphere P sorption. In addition, it was found that Mg in dolomite inhibited the formation of hydroxylapatite (HAP) while it promoted the formation of amorphous calcium phosphate (ACP). In the soil treatments amended with dolomite, soil CaCl2 –P (an indicator of P loss risk) decreased due to the surface P sorption while soil Olsen-P (an indicator of plant available P) increased. The latter is attributed to the dual effect of the competition between –OH and P and the inhibition of Mg to form stable HAP on dolomite.