Turnover and Losses of Phosphorus in Swedish Agricultural Soils: Long-Term Changes, Leaching Trends, and Mitigation Measures

Abstract

Transport of phosphorus (P) from agricultural fields to water bodies deteriorates water quality and causes eutrophication. To reduce P losses and optimize P use efficiency by crops, better knowledge is needed of P turnover in soil and the efficiency of best management practices (BMPs). In this review, we examined these issues using results from 10 Swedish long-term soil fertility trials and various studies on subsurface losses of P. The fertility trials are more than 50 years old and consist of two cropping systems with farmyard manure and mineral fertilizer. One major finding was that replacement of P removed by crops with fertilizer P was not sufficient to maintain soil P concentrations, determined with acid ammonium lactate extraction. The BMPs for reducing P leaching losses reviewed here included catch crops, constructed wetlands, structure liming of clay soils, and various manure application strategies. None of the eight catch crops tested reduced P leaching significantly, whereas total P loads were reduced by 36% by wetland installation, by 39 to 55% by structure liming (tested at two sites), and by 50% by incorporation of pig slurry into a clay soil instead of surface application. Trend analysis of P monitoring data since the 1980s for a number of small Swedish catchments in which various BMPs have been implemented showed no clear pattern, and both upward and downward trends were observed. However, other factors, such as weather conditions and soil type, have profound effects on P losses, which can mask the effects of BMPs.

Phosphorus Fate, Management, and Modeling in Artificially Drained Systems

“…Bergström et al (2015) in this issue provide an overview of Swedish research with more than 50 yr of field trial data and more than 25 yr small catchment data. At the catchment scale, soil properties and weather were found to have a greater influence on P loss to drainage waters than did placement of conservation practices.…”

“…In areas where P accumulates due to the concentration of livestock or high value-horticulture and/or vegetable production, accumulation of P in soils and sediments over the long term can create a source of P to drainage water that is extremely difficult to manage. Bergström et al (2015) review long-term soil fertility trials in Sweden, revealing strong positive relationships between soil P concentrations and dissolved P concentrations in leachate. Strategies are needed to draw down higher levels of soil P so that this legacy source of P to drainage water can be minimized.…”

“…Bergström et al (2015) reviewed Swedish studies evaluating best management practices (BMPs) to reduce P leaching losses including catch crops (i.e., cover crops), constructed wetlands, structure liming of clay soils, and manure management. At field and plot scales, the effects of BMPs on drainage P losses could be quite pronounced.…”

Quicklime application instantly increases soil aggregate stability

“…The application of limestone is a common agricultural management practice (VDLUFA, 2000), as considerable increases in crop yields have been reported (Haynes and Naidu, 1998). However, the application of quicklime has so far not become a standard procedure in agricultural soil management, although it has recently been mentioned as 'structural lime' together with slaked lime applied to diminish P leaching (Bergström et al, 2015;Ulén and Etana, 2014). So far, lime-treatment stabilisation studies using quicklime have focused on engineering geology and civil engineering to improve fine textured soil in terms of engineering properties for earthwork projects (Cuisinier et al, 2011;Hashemi et al, 2015;Metelková et al, 2012).…”

Spatially differentiated midpoint indicator for marine eutrophication of waterborne emissions in Sweden

“…Fixed removal rates are based on the assumption that the fate of P is directly correlated with fertiliser application and that it is equal for all soils and freshwater systems. In reality, P leaching and retention are highly variable and depend on factors such as soil properties, soil management and previous P loads (Bergström et al 2015). In contrast, the retention data for our transport factors are calibrated against field measurements (Brandt et al 2009), so it appears that Swedish conditions deviate from the generic removal rates assumed for EDIP 2003 CFs.…”