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Research article2016Peer reviewed

Use of a flashiness index to predict phosphorus losses from subsurface drains on a Swedish farm with clay soil

Ulen, Barbro; Stenberg, Maria; Wesström, Ingrid

Abstract

Risk assessment for elevated leaching losses of phosphorus (P) from agricultural land is commonly based on indices, since such losses are highly episodic and difficult to predict. Here a flashiness index (FI) representing changes in daily water flow from drainage systems was estimated from measured discharge (agrohydrological years 2004-2013) after reconstruction of subsurface drainage systems in 16 fields on a former swine farm. The fields were analysed for ammonium lactate-extractable soil P (P-AL), clay, carbon and other soil parameters in 2004. Transport of total P (TP), dissolved reactive P (DRP) and unreactive P (UP) was estimated from concentrations in composite water samples taken flow-proportionally up to 20 times per year. On average, 2.20 kg TP ha(-1) yr(-1) was leached, with 27% in DRP form, from the entire farm. Fir was significantly negatively correlated (Pearson correlation coefficient p < 0.05) to mean yearly discharge from each field. Stepwise regression demonstrated that FI index was the most important single explanatory parameter for flow-proportional yearly mean concentration of unreactive P losses (UP) from each field, with a coefficient of determination (r(2)) of 0.67. The corresponding concentration of dissolved reactive P (DRP) was significantly positively correlated (p = 0.015) to soil P-AL and FI. A regression model for TP leaching losses based on FI, P-AL and yearly discharge (03 from 11 of the fields over nine years (r(2) = 0.67, p = 0.002) was validated against TP leaching from the remaining five fields (32% of farm area). Root mean square error (RMSE) was 0.43, which represented 20% of measured leaching (mean 2.14 kg TP ha(-1) yr(-1)). For individual years, RMSE for different fields was 37-80% of measured TP leaching (0.8-3.7 kg TP ha(-1) yr(-1)). The Fl index could, be used together with soil P test to predict P leaching from individual fields of a drained farm. (C) 2016 Elsevier B.V. All rights reserved.

Keywords

Phosphorus soil status; Richards-Baker flashiness index; Subsurface drains

Published in

Journal of Hydrology
2016, Volume: 533, pages: 581-590