Page 92 - Plant-Based Remediation Processes

5 Impact of Metal/Metalloid-Contaminated Areas on Plant Growth 81

Fig. 5.1 Scheme of volume composition of mineral soil

(Mocek and Owczarzak 2011). Sources of organic colloids comprise substances
mainly of plant but partly also of animal origin that find their way to soil and there
they undergo mineralisation (about 70–80 %) and humification (about 20–30 %)
processes. Mineralisation involves the breakdown of organic matter into simple
mineral compounds such as CO 2 ,H 2 O, and NH 3 . Humification, on the other hand,
is a process of transformation of organic residues in soil resulting in soil humus
(Bednarek et al. 2004). Humus can be defined as a complex and relatively stable
mixture of brown or dark-brown colloid substances (organic and organic-mineral)
developed as a result of degradation of primary tissues, mainly of plant origin, and
synthesis by various soil organisms (Brady 1990; Prusinkiewicz 1999).
Solid phase chemical composition exerts a decisive role regarding soil nutrient
availability and not, as often wrongly claimed in the literature, soil fertility. Soil
fertility is a much wider concept because it emphasises soil capability to meet
edaphic requirements of various plants within the framework of possibilities
created by the remaining site conditions (Prusinkiewicz 1999). Therefore, it may
be concluded that fertile soil is a soil rich in nutrients (both macro- and
microelements) and characterised by stable (appropriate) air–water parameters. In
other words, every fertile soil must be rich in nutrients, but not every nutrient-rich
soil can be considered as fertile. Mineral constituents essential for plants can be