Theory question 103
Soil Properties(a) State four characteristics of clay.
(b) Mention four effects of drought on plant growth and development.
(c) List two symptoms of phosphorus deficiency in crops.
(d) State three ways in which each of the following soil properties is important in crop production: (i) soil reaction; (ii) soil temperature.
Show the model answer
(a) Any four: very fine particles (below 0.002 mm); high water-holding capacity; poor drainage and aeration; sticky and plastic when wet, hard and cracked when dry; high nutrient and cation exchange capacity; heats and cools slowly.
(b) Any four: wilting; reduced leaf area and stunted growth; delayed flowering or flower/fruit drop; poor germination and crop establishment; reduced photosynthesis; low yield or death of plants.
(c) Any two: stunted growth; purple or reddish leaves; poor root development; delayed maturity; poor fruit and seed formation.
(d)(i) Soil reaction (pH): affects availability of nutrients; affects activity of soil micro-organisms; decides which crops grow well; very low pH makes some elements (Al, Mn) toxic.
(ii) Soil temperature: affects seed germination; affects root growth and nutrient uptake; affects activity of micro-organisms and decomposition; affects evaporation of soil water.
Part (d) needs three points for each of the two properties.