A simplified risk assessment for losses of dissolved reactive phosphorus through drainage pipes from agricultural soils |
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| Authors: | B Ulén |
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| Institution: | 1. Department of Soil Sciences, Division of Water Quality Management , Swedish University of Agricultural Sciences , Uppsala, Sweden barbro.ulen@mv.slu.se |
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| Abstract: | Abstract Soil tests with extractions are commonly used for risk assessments of phosphorus (P) leaching. Procedures for routine analysis of crop-available soil P by extraction with acid ammonium lactate (P-AL) have been used for nearly 50 years in Sweden, Norway and several East European countries. Aluminium and iron (Al-AL and Fe-AL) were determined in the same extract for 40 well known clayey, loamy or sandy soils from the Swedish long-term studies. Average outcome was 16.8 and 6.0% for the two elements related to extraction with chelating ammonium oxalate (Al-AO and Fe-AO) and concentrations had a correlation coefficient of 0.947 and 0.891, respectively, when the two extraction agents were compared. On average, P-AL determination using inductive coupled plasma (ICP) resulted in 19% higher soil P concentrations compared to analysis using a colorimetric method based on non-calcareous and calcareous soils from the southern counties in the Swedish soil survey, represented mainly by sandy loam soils. Degree of P saturation on a molar basis in the AL extract (DPS-AL) was determined for 22 Nordic observation fields with drained clayey, loamy and sandy soils. Results were used together with long-term flow-weighed concentration of dissolved reactive P (DRP) concentration in drainage water. These parameters were correlated (r=0.918, p=0.000) and could be fitted to a linear regression model (R2=84.3). In addition, two fields with unusually high DPS-AL values could clearly be identified as those with lowest P sorption index and highest DRP concentrations in drainage water. This demonstrates DPS-AL to have the potential as an environmental risk indicator for Swedish acid soils. A set of 230 non-calcareous soils in the southern counties of Sweden from the Swedish soil survey indicated that 3% of the soils had a high DPS-AL in the topsoil or subsoil, from which high DPS leaching probably occurs. |
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| Keywords: | Drainage water P concentration Soil degree of P saturation |
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