(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) 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
