## 3 Results and Discussion
### Effect of Treated Sludge on Yield, Composition and Nutrient Uptake by White Clover
As far as the alkaline soil treatments are concerned, the highest total and aboveground biomass yields were observed in the bentonite- and biochar-treated sludge treatments (AlBc, AlB), which were also similar to the yields of the air-dried sludge (AID) and the inorganic fertilization treatments (Figure 1b). Aboveground biomass yields significantly increased by 153, 147, 116, 114 and 107% in AlBc, AlB, AlIF, AlD and AlIFX treatments, respectively, compared to the control. According to root biomass yields, treatments followed the order AlB > AlBc > AlD > AIL > AIIF > AIC > AIV > AIFX. The nitrogen, P, K, Ca and Mg contents of white clover plants grown in alkaline soil treatments were within the common range [19; 47] and the respective concentrations were 26.6-42.8, 1.7-2.2, 27.6-37.7, 14.3-42.1 and 3.2-52 g kg\({}^{-1}\). Plant uptake of macronutrients followed the same pattern as biomass yield and the poor effect of treatments with lined and vermiculite-treated sludge (AIL, AlV) on white clover yield was accompanied by reduced N, P and K uptake (Figure 2b). Figure 1: Aboveground and total dry biomass yield of white clover plants, grown in (**a**) acid soil treatments and (**b**) alkaline soil treatments. Treatment of the acid and alkaline soil, respectively, with: AcB and AlB: bentonite-treated sludge; AcV and AlV: vermiculite-treated sludge; AcB and AlBc: biochar-treated sludge; AcL and AIL: lined sludge; AcD and AID: air-dried sludge; AcLF and AIIF: N-P-K inorganic fertilization; AcIFX and AlIFX: P-K inorganic fertilization; AcC and AIC: control. Different letters, within each soil and property, indicate significant differences among means, using the LSD test, at \(p\leq 0.05\). Soil pH increments promoted the availability and, consequently, the plant uptake of Cu, Zn and B in the acid soil treatments with bentonite- or vermiculite-treated or untreated sludge, compared to the control and also to the inorganic fertilization treatments (Figure 3a). Conversely, plant uptake of almost all micronutrients after the treatment with the lined sludge (AcL) was similar to or lower than the control, probably because of the strongly alkaline reaction of the specific treatment. It was observed that Zn uptake was depressed in the treatment with the biochar-treated sludge (AcBc) (Figure 3a); although no effect of the particular treatment on soil-available Zn was observed. Concentrations of Cu, Zn, Fe, Mn and B in white clover plants grown in acid soil treatments were either within usual ranges or excessive [19; 47] and ranged between 11.3 and 42.4, 18.5 and 53.5, 341 and 1376, 179 and 1326 and 54.1 and 69.7 mg kg\({}^{-1}\), respectively. Concentrations of Ni, Cd, Pb and Hg were not detectable in all of the treatments of both soils. In agreement with these findings, increased metal uptake has been reported for white clover plants grown in sewage sludge-amended soils with a pH of 5.1 [15]. In all alkaline soil treatments, micronutrient uptake occurred at levels several times lower than acid soil treatments, probably because the pH remained close to the initial strongly alkaline value in all cases (Figure 3b and compared with Figure 3a). However, Zn uptake increased in all treatments with sludge  
Figure 2: Uptake of macronutrients by white clover plants, grown in (**a**) acid soil treatments and (**b**) alkaline soil treatments. Treatment of the acid and alkaline soil, respectively, with: AcB and AlB: bentonite-treated sludge; AcV and AlV: vermiculite-treated sludge; AcBc and AlBc: biochar-treated sludge; AcL and AIL: lined sludge; AcD and AID: air-dried sludge; AcIF and AIIF: N-P-K inorganic fertilization; AcIFX and AIIFX: P-K inorganic fertilization; AcC and AIC: control. Different letters, within each soil and property, indicate significant differences among means, using the LSD test, at \(p\leq 0.05\). in comparison to the control and inorganically-fertilized treatments (Figure 3b), despite the strongly alkaline pH.