*2.1. Material*

The MIBA used in this work originated from a full-scale WtE-incineration plant in southwestern Sweden. The waste, mainly municipal and industrial waste, was incinerated in four grate-fired furnaces with steam boilers that produced electricity and district heating. Bottom ash was collected from all lines, mixed, and stored in large piles that were naturally weathered, i.e., not sheltered against wind or water, for at least 6 months. After 1–3 months in storage, metal pieces (>~2 mm) were mechanically removed using mobile sorting equipment with magnets and eddy current magnets. Sub-samples from the MIBA were collected and mixed to form one sample of about 600 kg, which was used for the cultivation tests.

For the control cultivation, where sunflowers and rapeseed were cultivated under normal circumstances, a commercial "lean planting soil" generated from the biological treatment of garden waste was used (Table 1) (Reference soil) [26]. To promote plant growth, and to study the effect of fertilizer on this growth, the reference cultivation boxes and half of the cultivation boxes containing MIBA were fertilized with YaraMila Promagna 11-5-18. This fertilizer is specially developed for plants with a high need for N, which is a shortage in MIBA [27].
