Mobility of heavy metals in sandy soil after application of composts produced from maize straw, sewage sludge and biochar: Discussion of Gondek et al. (2018).

Gondek et al. (2018) investigate the mobility of heavy metals in sandy soil after application of composts produced from maize straw, sewage sludge and biochar. The authors made a little attention to role of the soil properties and soil condition on the metals chemical behavior. In different section of the paper, the authors reported that the content of the metals extracted with water or 1 M NHNO was changed compared to the control treatment affected by the mentioned biosolids. Nowadays, different researches have shown that the trace metals nature have an important role in determining their fate in presence of different treatments. In addition to, organic compounds entered to the soil due to biosolids applications have a duplicate role in trace metals mobility. Therefore, it is needed this facts are considered to interpret the measurements in the original paper. Also, whenever effects of different materials are studied on the metals mobility, the metals status in the plant tissues presents valuable information to the scientists and readers for carefully interpreting the measurements, which it is ignored by the authors.