Abstract
Appropriate management of animal waste is essential for guaranteeing good water quality. A laboratory leaching study with intact soil columns was performed to investigate the risk of phosphorus (P) leaching from a clay loam and a loamy sand. The columns (0.2 m deep) were irrigated before and after application of pig slurry on the surface or after incorporation, or application of mineral P, each at a rate of 30 kg P ha-1. The two soils had different initial P contents (i.e. the ammonium lactate-extractable P was 65 and 142 mg kg-1 for the clay loam and loamy sand, respectively), but had similar P sorption characteristics (P sorption index 3.0) and degree of P saturation (17-21%). Concentrations of dissolved reactive P (DRP) and total P (TP) before P application were significantly higher in leachate from the loamy sand (TP 0.21 mg L-1) than from the clay loam (TP 0.13 mg L-1), but only increased significantly after P application to the clay loam. The highest concentrations were found when slurry was surface-applied (DRP 1.77 mg L-1), while incorporation decreased the DRP concentration by 64% in the clay loam. Thus moderate slurry application to a sandy soil with low P saturation did not pose a major risk of P leaching. However, application of P increased the risk of P leaching from the clay loam, irrespective of application method and despite low P saturation. The results show the importance of considering soil texture and structure in addition to soil chemical characteristics in risk assessments of P leaching. Structured soils such as the clay loam used in this study are high risk soils and application of P to bare soil during wet periods, e.g. in autumn or spring, should be followed by incorporation or avoided completely.
Highlights
Reduction of phosphorus (P) losses from arable land is of major concern within the work to reduce eutrophication of waters, as for example the Baltic Sea in northern Europe (Boesch et al 2006)
Concentrations and leaching of P under baseline conditions In general, the loamy sand had higher amounts of leachate and P leaching than the clay loam before P applications (Table 4)
dissolved reactive P (DRP) accounted for 67% of the concentrations of total P (TP) in leachate from the loamy sand, while only 38% from the clay loam
Summary
Reduction of phosphorus (P) losses from arable land is of major concern within the work to reduce eutrophication of waters, as for example the Baltic Sea in northern Europe (Boesch et al 2006). The processes behind P losses are complex and influenced by natural factors, such as soil properties, topography and weather conditions, as well as by different management practices in the field These practices include for example crops, cropping sequences, fertilizer applications (Sharpley et al 2004; Sims et al 1998) and soil tillage (Ulén et al 2010). Single applications of mineral or organic fertilizers may constitute a direct risk of P losses, especially if applied in large amounts and/or during conditions with risk of surface runoff or leaching This risk is mainly attributed to structured soils as clay and clay loams, where macropores may provide rapid transport of solutes and particles (Jarvis 2007). For coarse-textured soils without macropores, the direct risk of P leaching losses after application of P is generally low due to adsorption of P (van Es et al 2004; Glæsner et al 2011; Sørensen and Rubæk 2012)
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