(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]
(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
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