Page 25 - Curriculum Visions Dynamic Book. To close the book, close the tab.

Humus
Horizon, soil
A distinctive layer in a soil. It is
a word used by soil scientists. Gardeners use the words topsoil and subsoil to refer to A horizons and B horizons, respectively.
The rock or other material on which a soil forms is called the parent material and is designated as the C horizon.
 Horizon, soil – Soils are divided into layers called horizons. The main ones are A, B and C, sometimes subdivided to describe important features.
 Halite – Crystalline halite is called rock salt. is the most widespread form of iron
ore. (See also: Botryoidal.)
Halide minerals
A group of minerals – for example, halite (rock salt) – that contain a halogen element (elements similar to chlorine) bonded with another element. Many are evaporite minerals.
Halite
A mineral made of sodium chloride. It is normally called rock salt. It occurs in thick beds that represent former dry lake or lagoon beds. (See also: Chemical rock; Crystalline; Evaporite.)
Heavy soil
A soil that is difficult to cultivate because it is dominated by clays. Heavy soils are improved by treating them with manure and calcium. Both of these materials help the clay form clumps (see: Crumb structure; Flocculation) and so drain better. Heavy soils may also need to be drained.
Hexagonal
A crystal system in which the crystals have three axes all at 120° to one another and of equal length (see: Axis of symmetry). Beryl is a mineral of this system.
Topsoil (A horizon); mixture of
A organic and mineral matter. Main
zone of fibrous plant roots.
Subsoil (B horizon); little organic
B matter and mostly water-seeking
taproots.
Parent material (C horizon); mineral material from which the upper soil horizons form (may be solid rock or loose material such as alluvium).
C
Hornblende
A dark-green silicate mineral containing sodium, potassium, calcium, magnesium, iron and aluminium. Hornblende is a common mineral in rocks such as basalt and gabbro. (See also: Ferromagnesium mineral.)
Humus
Decomposed organic matter in a soil. Humus is vital for two reasons. Firstly, it contains large
amounts of nitrogen and potassium, which are essential nutrients for growing plants. Secondly, it contains threads of sticky substances that bind soil particles together and keep the fine clay particles from clogging up the soil or from being blown away in a strong wind. A soil should have
at least 1% humus to be fertile. (See also: Alfisol; Black soil; Chernozem; Compost; Crumb structure; Moder; Mor; Mulch.)
25