Chemically Precipitated Struvite Dissolution Dynamics Over Time in Various Soil Textures

Abstract - Phosphorus (P) is a fundamental nutrient in agricultural production and is one of three major components in common fertilizers. The majority of fertilizer-P sources are derived from phosphorus rock (PR), which has finite abundance, thus a sustainable source of P is imperative for future agricultural productivity. A potential sustainable P source may be the recovery of the mineral struvite (MgNH4PO4 ·6H2O) from wastewater treatment plant effluent, but struvite behavior in soils of varying texture are not well characterized. The objective of this study was to assess the dissolution dynamics of a commercially available, wastewater-recovered struvite product over time in a plant-less, moist-soil incubation experiment with multiple soil textures. Chemically precipitated struvite (Crystal Green; CG) from municipal wastewater in pelletized and finely ground forms were added to soil cups at a rate of 24.5 kg P ha-1 containing soils of varying texture (i.e., loam, silty clay loam, and two different silt loams) from agricultural field sites in Arkansas. Soil cups were destructively sampled five times over a 6-month period to examine the change in water-soluble (WS) and weak-acid-extractable (WAE) P, K, Ca, Mg, and Fe concentrations from their initial concentration. After 0.5 months, both WS-P and WAE-P concentrations increased (P < 0.05) more from initial concentrations of the finely ground CG in all soils, which averaged 76.2 and 158 mg kg-1, respectively, than in the pelletized CG treatment, which averaged 14.0 and 12.2 mg kg-1, respectively, across all soils. Over the course of the 6-month incubation, WS- and WAE-P concentrations generally increased over time in the pelletized and decreased over time in the finely ground treatment, confirming the slow-release property of pelletized CG that has been previously reported. Results of this study provide valuable insight regarding struvite-P behavior in various soils and provide further supporting evidence for the utilization of struvite as a potential alternative, sustainable fertilizer-P source.

摘要 - 磷（P）是农业生产的核心营养元素，亦是常见肥料的三大主要组成成分之一。绝大多数肥料磷源均源自磷矿石（phosphorus rock, PR），而磷矿石储量有限，因此可持续磷源对未来农业生产力至关重要。从污水处理厂出水回收矿物鸟粪石（struvite, MgNH₄PO₄·6H₂O）是潜在的可持续磷源，但不同质地土壤中鸟粪石的行为特征尚未得到充分表征。本研究旨在通过多质地土壤无植株湿润土壤培养试验，评估市售污水处理回收鸟粪石产品随时间推移的溶解动力学过程。研究中将市政污水化学沉淀制备的颗粒状与细磨型鸟粪石产品（Crystal Green, CG）以24.5 kg P ha⁻¹的施用量，添加到取自阿肯色州农田的四种不同质地土壤（即壤土、粉砂质黏壤土以及两种不同的粉砂壤土）的土壤杯中。在6个月的培养周期内分5次进行破坏性取样，以测定水溶性（water-soluble, WS）与弱酸提取态（weak-acid-extractable, WAE）磷、钾、钙、镁、铁的浓度相对于初始浓度的变化。培养0.5个月后，所有土壤中细磨CG处理的水溶性磷（WS-P）与弱酸提取态磷（WAE-P）浓度较初始值的增幅（分别平均为76.2 mg kg⁻¹与158 mg kg⁻¹）均显著高于颗粒状CG处理（分别平均为14.0 mg kg⁻¹与12.2 mg kg⁻¹，P < 0.05）。在6个月的培养过程中，颗粒状CG处理的WS-P与WAE-P浓度总体随时间升高，而细磨处理则随时间降低，这证实了此前报道的颗粒状CG的缓释特性。本研究结果为阐明不同质地土壤中鸟粪石磷的行为特征提供了宝贵见解，并为鸟粪石作为可持续替代肥料磷源的应用提供了进一步的佐证。