(a)In an experiment on soil porosity, the following measurements were taken and recorded: Volume of dry soil = 50 cm³, Volume of water = 50 cm³, Total volume of soil and water = 75 cm³. Use the above information to (i) find the volume of air space in the soil sample. (ii) calculate the porosity of the soil sample. (b) Mention three reasons why soil porosity is important in agriculture. (c) State four characteristics of each of igneous and sedimentary rocks.
Explanation
(a)(i) Expected total volume of soil and water = 50cm³ + 50cm³ = 100cm³ Actual or given total volume of air and water = 74cm³ Difference in total volume = 100cm³ — 74cm³ The difference represents air space volume = 26cm³ (ii) Porosity of the soil sample = volume of air space in the soil divide volume of soil sample x 100% 26cm³/50cm³ x 100/1 = 260/5 = 52 % (b) Reasons why soil porosity is important in agriculture: It influences: (i) exchange of gases by the roots/soil aeration (ii) the water retention capacity of soil (iii) nutrient availability in soil (iv) the microbial activities in the soil (v) the pH level of soil (vi) and enhances root penetration in the soil. (c) Characteristics of: (i) Igneous rocks (a) glassy appearance (b) crystalline appearance (c) light and dark in colour (d) hard or very hard to touch (e) compact (ii) Sedimentary rocks: (a) appear in layers, sheets or strata (b) coarse textured (c) animal/plant remains may be present (fossils) (d) soft (e) reacts with weak acids e.g. dilute HCL, Carbonic acid does not dissolve in water.
