Concentration and offtake of trace elements and macronutrients in Italian ryegrass (Lolium multiflorum Lam.) and spring barley (Hordeum vulgare L.) grown on soils amended with water treatment residual sludge
Aluminium sulphate (Al2(SO4)3) is usually added during the drinking water treatment processin order to precipitate organic and inorganic material, resulting in aluminium-based drinkingwater treatment residual sludge (WTR). Since 2003 Swedish law no longer permits WTR tobe deposited in lakes, and there is an interest to explore the possibility to utilize WTR as soilamendment. The aim of this study was to examine the effects of WTR application on cropgrowth and concentrations of macronutrients and trace elements (including micronutrients andpotential toxic elements). A greenhouse pot experiment was conducted with three soils; a clayloam rich in phosphorous (P), a loamy sand rich in P, and a silty loam with a low soil Pconcentration, and two crop species Italian ryegrass (Lolium multiflorum Lam. cv. Fredrik)and spring barley (Hordeum vulgare L., cv. Barbro) mainly used as livestock feed. Addition ofWTR at a rate of 30 tons (t) ha-1 revealed significantly higher yields (6.3 t ha-1) of Italianryegrass harvested twice, compared with a control without WTR addition (4.1 t ha-1) for a clayloam. The corresponding value for a loamy sand was 7.0 t ha-1 with WTR compared with 4.1 tha-1 for the control. For the third soil studied, a silty loam, yield was only marginally higherwith WTR addition. Significantly higher yields were also found after application of 15 t ha-1WRT to these soils. .In contrast, spring barley showed no significant increase in yield afterWTR application on any of the three soil types. Concentrations of copper (Cu) weresignificantly higher in Italian ryegrass grown with WTR application (mean 9.3 mg kg-1)compared with the control (7.2 mg kg-1). Both Italian ryegrass and spring barley grown on aclay loam took up a significant amount of sulphur (S) from the WTR-amended soils comparedwith the same soil with no amendment. On a clay loam with high soil concentrations of Cu(25 mg kg-1), Cu offtake with Italian ryegrass was 0.049 kg ha-1. Molybdenum (Mo), and zinc(Zn) may have been limiting for the growth of Italian ryegrass and spring barley, since theirconcentrations in plants were significantly higher (28 mg kg-1 Mo and 32 mg kg-1 Zn) withoutWTR application than at the higher load (30 ton ha-1) of WTR applied (9 mg kg-1 Mo and 30mg kg-1 Zn). Concentrations of the trace elements Ni, Mo, Cu, Zn were below the limitconsidered toxic to ruminants. However, the latter has only been poorly investigated.Drinking water treatment residuals could be applied to soils like the clay loam and loamy sandstudied here as soil amendments when growing crops such as Italian ryegrass and springbarley. For the silty loam, no positive effects or negative effects were apparent.