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Phosphorus (P) leaching from agricultural soils is a serious environmental concern. Application of aluminium water treatment residuals (Al-WTR5) at a rate of 20 Mg ha-1 to clay soils from central Sweden significantly increased mean topsoil P sorption index (PSI) from 4.6 to 5.5 imol kg-1 soil. Mean degree of P saturation in ammonium lactate extract (DPS-AL) significantly decreased from 17 to 13%, as did plant-available P (P-AL). Concentrations of dissolved reactive P (DRP) decreased by 10-85% in leaching water with Al-WTR treatments after exposure of topsoil lysimeters to simulated rain. Soil aggregate stability (AgS) for 15 test soils rarely improved. Three soils (clay loam, silty loam and loam sand) were tested in greenhouse pot experiments. Aluminium-WTR application of 15 or 30 ton ha-1 to loam sand and a clay loam with P-AL values of 80-100mg kg-1 soil significantly increased growth of Italian ryegrass when fertilised with P but did not significantly affect growth of spring barley on any soil. Al-WVR should only be applied to soils with high P fertility where improved crop production is not required. [ABSTRACT FROM AUTHOR]

Abstract: Concentrations of dissolved reactive phosphorus (CDRP) and particle-bound phosphorus (CPP) were investigated in soil columns taken from different parts of three selected agricultural fields. The columns (mini-lysimeters 20cm in diameter, 20cm high) were exposed to on average 64±6mm of simulated rainfall. Total phosphorus concentrations (CTP) in water percolating from the lysimeters were similar to the CTP observed in drainage water leaving the fields, but the CDRP/CTP ratio was significantly (p <0.001) higher in the percolate. The high CDRP (up to 0.4mgL−1) measured in the percolate may have partly derived from decomposition of accumulated senescing vegetation and litter material, since CDRP in percolating water was related to total organic carbon concentration (TOC) in the shallow topsoil (0–5cm) and to phosphorus concentration in soil extract of ammonium lactate (P-AL) from the same soil layer. Another easily identified factor clearly related to CDRP in percolate from the lysimeters was the degree of phosphorus saturation (DPS) in the same soil P-AL extract. The factors giving best prediction of CPP and leaching were the amount of percolate passing through the soil columns and total phosphorus concentration in the topsoil determined after oxidation with nitric acid (TP-HNO3). One field under grass ley, including the slope and depression close to the field outlet, comprised 24% of total field area. In the other two fields these areas (11 and 17% of total area respectively) were under long-term permanent green fallow as an internal buffer zone (IBZ). The lysimeter studies indicated that these areas had a higher risk of DRP losses than the rest of the fields. In addition, the P content of the particles in water from the depression was unusually high. Aggregate stability, measured indirectly as readily dispersible clay and expressed as nephelometric turbidity units (NTU), was significantly stronger at the lowest point of one IBZ (27–35NTU) than in stubbled parts of the same field (62NTU), and the turbidity of water percolating through the topsoil was lower (5–27NTU). [Copyright &y& Elsevier]

Abstract: Phosphorus (P) binding to minerals and ion exchange capacity in different clay fractions were examined for a non-calcareous soil in southwest Sweden. The soil had received pig slurry during three decades, 2 kg lower than the recent maximum load of 22 kg P ha−1 year−1 as regulated by livestock density legislation. The topsoil was found to contain 33% clay by weight. Illite was the predominant clay mineral and constituted 13% of total soil. Vermiculite (10%), K-feldspar (14%) and plagioclase (21%) also constituted significant proportions of the mineralogical matrix. Within the most fine-grained clay fraction, 50% of which was less than 0.1 μm in particle size, illite and vermiculite dominated totally, 50 and 23% respectively. In fine-grained (FG), most fine-grained (MFG) and colloidal fractions, there were strong relationships (Pearson correlation coefficient 0.98–1.00) between calcium (Ca) and P. There was a low molar ratio Ca:P in added manure and the presence of Ca–P complexes in the fine soil fractions was indicated. In contrast, in the coarse soil fraction (>2 μm), there was a clear relationship (Pearson coefficient 0.97) between P and iron oxide (Fe2O3) and between P and aluminium oxide (Al2O3) throughout the soil profile. Thus even for non-calcareous soils, formation of Ca–P complexes should be taken into account with regards to losses of colloidal P to drainage water. [Copyright &y& Elsevier]