(a) What is soil consistency?
(b) Explain how each of the following soil properties influences crop growth:
(i) soil texture; [2 marks]
(ii) soil pH. [4 marks]
(c) (i) List four methods by which soil fertility could be maintained. [2 marks]
(ii) Explain two ways in which each of the methods listed in 3(c)(i) contributes
to the maintenance of soil fertility. [8 marks]
Explanation
(a) Meaning of soil consistency
Soil consistency is the resistance of soil to pressure and other physical manipulation
(b) Explanation on how soil properties influence crop growth
(i) Soil texture
-Determines water holding capacity of soils
-Influences air movement in the soil
- Affects root penetration
-Affects soil workability
-Has direct effect on soil drainage/infiltration
-Affects the retention of plant nutrients
(ii) Soil PH
-Generally, extreme pH values affect the activities of soil micro-organisms
-Affects the availability of plant nutrients
- Affects the solubility of certain elements which may be toxic to crops at high concentration
-Crops perform poorly outside their required pH range
-Controls cation exchange capacity (C.E.C.) of the soil
(c)(i) Methods by which soil fertility could be maintained
-Fallowing (as in land rotation)
-Alley cropping
-Crop rotation
-Mixed cropping
-Mixed farming
-Cover cropping
-Application of organic/inorganic fertilizers
- Liming
(ii) Ways in which each of the methods contributes to the maintenance of soil fertility
-Fallowing (as in land rotation)
-Deep rooted plants extract leached nutrients which will eventually be returned to the top soil
-Dead plants decompose and add humus to the soil
-Activities of soil micro and macro-organisms add organic matter to the soil under the fallow system
- Dead plants add nutrients to the soil
Alley cropping
- Through nitrogen fixation by the leguminous plants
- Litter from the trees decompose and add humus to the soil
- Litter from trees decompose to release nutrients to soil
-Litter acts as mulch to control erosion
Crop Rotation
-Crops that feed deep in the soil extract plant nutrients from below leaving nutrients in the upper layer for the surface feeders to us
-Legumes incorporated in the rotation can replenish the land
- Constant vegetation cover checks soil erosion
Liming
- Addition of lime provides basic cations e.g. Calcium and Magnesium
- Liming raises soil pH making nutrients like phosphorus more available
- Liming increases the cation exchange capacity of soils
Mixed cropping
- If leguminous plants are included, nitrogen will be added to the so and this improves soil fertility
- Crops with different rooting systems will extract nutrients from different depths of soil
Mixed farming
- Animal droppings add nutrients to the soil
- Animal droppings increase the cation exchange capacity of the soil
- The microbes in the droppings assist in the decomposition of plant remains falling on the soil
Cover crops
-Protects the soil against erosion
- Fixes atmospheric nitrogen into the soil when leguminous crops are used
-Dead leaves of plants are decomposed to increase soil fertility
-Creates conducive environment for increased microbial activities
Application of organic? inorganic fertilizers
- Increases cation exchange capacity of the soil when organic manure is applied
-Adds nutrients to the soil
-Raises soil pH when lime is applied
-Lowers the soil pH when acidulants are added e.g. pyrite. gypsum