Write short notes on the following: (a) soil pH; (b) soil texture; (c) soil organisms; (d) soil profile.
Explanation
(a) Soil pH: (i) Is the concentration of hydrogen ions (H-) in the soil. (ii) determines the acidity, alkalinity or neutrality of the soil (iii) dictates crops grown/distribution. (iv) crops thrive well within pH range of 5.5 - 7.5 (v) It influences availability of nutrients for plant growth. (vi) influences the types and number of organisms in the soil
(b) Soil Texture (i) refers to the relative proportion of different sizes of mineral particles in the soil. (ii) This includes sand, silt and clay (iii) it determines the degree of coarseness or fineness of a soil sample/or soil consistency. (iv) the proportion of the different fractions determines the type of the soil. (v) coarse sand: 2.0 - 0.2mm, fine sand : 0.2 - 0.02mm, silt: 0.02 - 0.002mm, clay: less than (vi) soil texture tends to be the most consistent physical property (vii) determines the types of crops to be grown.
(c) Soil Organisms: (i) include micro and macro soil-living organisms, (micro cannot be seen with naked eyes, while macro can be seen (ii) soil organisms are involved in the decomposition of dead organic matter in the soil. iii are bacteria, fungi and algae. (iv) assist in other chemical changes as in the carbon and nitrogen cycles. (v) Also helps in burrowing, which paves way for aeration and movement of water in the soil. (vi) earthworms, termites, ants and others others are also important in the decomposition of plant residues in the soil. (vii) some bacteria fix atmospheric nitrogen while living in a host plant, usually a leguminous plant, e.g. Rhizobium inhabiting the root nodules (viii) some soil micro-organisms help improve soil structure. (ix) some soil micro-organisms can be harmful/destructive. (x ) some soil micro-organisms produce acidic materials which help to break down rocks.
(d) Soil Profile: Vertical section of the soil from the surface into the underlying unweathered materials. - The different soil colour and texture between each layer of soil are recognised and referred to as horizons. - The A - Horizon (or Top Soil) is made up of partly decayed plant and animal materials and humus. This portion is dark in colour. - The B-Horizon or Sub-soil contains mineral elements and clay. The colour is greyish or brown. - The C-Horizon or Weathered Parent Material is made up of materials produced from the parent rock. It has high clay materials. - The last layer, called D - Horizon or Bed rock is unweathered rock.