Theory question 104
Soil Properties(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 = 74 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.
Show the model answer
(a)(i) Volume of air space = (50 + 50) − 74 = 26 cm³
(ii) Porosity = 26/50 × 100 = 52%
(b) Any three: pores hold air for root and microbe respiration; pores hold water; allows drainage and infiltration; allows root penetration; affects soil temperature
(c) Igneous (any four): formed from cooled magma; crystalline; hard and compact; no layers or fossils; e.g. granite, basalt
Sedimentary (any four): formed from deposited particles; in layers (stratified); may contain fossils; usually softer; e.g. sandstone, shale, limestone
Show the subtraction and the percentage working.