QUESTION 1

1. Define the following terms (3mks).

Answer:

1. i) Organic farming

Is a form of agriculture that relies on activities such as crop rotation, green manuring,

composting and biological pest control but avoid the use of manufactured inorganic substances.

1. ii) Weathering

Is the breakdown of rock materials into small particles and eventually into soil (1mk)

 

1. State any three factors that determine soil colour (3mks)

Answer:

1. i) Humus content
2. ii) Level of the hydration of the soil

iii) Chemical nature of the compounds in the soil

(Each 1mk, maximum 3 points)

 

1. Briefly describe the mechanical analysis of particle texture group by the method of dispersion in water.(5mks)

Answer:

 

– A sample of soil with as little as amount of organic matter as possible is put in a glass of cylinder.

-Add water to the soil almost to the brim and shake vigorously

-Let the cylinder stand for several minutes. It is observed that the particles of the soil will arrange themselves according to their sizes along the height of the cylinder.

-The biggest particles will settle at the bottom and the smallest at the top.

-Measure the height of each column using a ruler. The height will be used to calculate the proportion of each type of particles in the soil sample.

(Each point 1mk, maximum 5 points)

 

1. Outline four importance of soil water to plant growth (4mks)

Answer:

-Acts as a solvent of plant nutrients

-Helps to maintain soil turgidity and hence plant support

-Required in such processes such as photosynthesis and germination

-Creates a good medium for microbial activities

-Helps in control of soil air

-Helps in control of soil temperature

-Helps to cool the plants through the process of evapotranspiration

(Each point 1mk, maximum 4 points)

 

QUESTION 2

1. Differentiate between physical and chemical weathering. For each state one agent involved in the process (4mks).

Answer:

-Physical weathering is the breakdown of rock materials into small fragments without any chemical change.

-Chemical weathering is the decomposition of rock into other mineral matter by chemical agents

-Examples of chemical agents  are water, carbon dioxide, weak acid and oxygen.

(Each point 1mk, maximum 4 points).

 

1. State 3 characteristics of horizon ‘B’ of a soil profile

Answer:

-Is a layer of maximum accumulation (illuviation) of leached minerals.

-It is poorly aerated.

-Has little or no organic matter

(Each point 1mk, maximum 3points)

 

1. Differentiate between soil texture and soil structure (2mk)

Answer:

-Soil texture is the relative proportion of sand, silt and clay in the soil

-Soil structure is the arrangement of soil particles in aggregates of varying consistence

(Each point 1mk, maximum 2 points)

 

1. State the four major soil textural classes (4mks)

Answer:

-Sand

-Silt

-Clay

-Loam

(Each point 1mk, maximum 4 points)

 

1. Outline any two ways of improving soil structure (2mks)

Answer:

-Addition of organic matter to the soil

-Liming of the soil

-Growing of legumes and grasses

-Mulching

-Draining of the soil

-Minimum tillage

-Working on the soil at the right moisture content

(Each point 1mk, any 2 points)

 

QUESTION 3

1. State three factors that influence soil temperature (3mks)

Answer:

-Solar radiation

-Atmospheric temperature

-Soil colour

(Each point 1mk, maximum 3 points)

 

1. List four components of soil air (2mks)

Answer:

-Oxygen

-Carbon dioxide

-Nitrogen

-rare gases

(Each 1/2mk, maximum 4 points)

 

 

 

1. Briefly explain three ways through which soil organisms are beneficial (6mks)

Answer:

-Increase soil fertility and productivity.

The organisms especially the micro-organisms facilitate the decomposition of organic matter. This releases mineral nutrients into the soil. Furthermore, there is production of humus which improves soil structure.

 

-Nitrogen fixation

Some micro-organisms help in the fixing of atmospheric nitrogen into a form readily available to plants.

 

-Decomposition of residues

The decomposition of toxic residues of organic compounds used in agriculture is carried out by micro-organisms

 

 

1. Explain two importance of soil air (4mks)

 

Answer:

-Soil air contains oxygen.

Oxygen is necessary for the respiration of the plant roots and that of aerobic micro-organisms.

-Soil air contains nitrogen.

The nitrogen is fixed into available forms by the help of bacteria hence improving soil fertility.

 

 

QUESTION 4

 

1. Explain how any three plant factors affect the rate of decomposition of organic matter (6mks).

 

Answer:

-Age of plants

Yong plants decompose faster than older plants

 

-Type of species of the plant

Some species of plants decompose faster than others

 

-Chemical composition

Some plants have chemicals that hinder the decomposition process

 

 

1. List four importance of humus (4mks)

 

Answer:

-Source of nutrients for plant growth

 

-Improvement of soil through binding of soil particles into aggregates

 

-Acts as a pH buffer

 

-Influences plant diseases e.g micro-organisms in humus course disease to plants.

 

-Conserve nitrogen in the soil through the adsorption process.

 

(Each point 1mk, maximum 4 points)

 

 

 

c)State four ways through which organic matter is lost from the soil (2mks)

 

Answer:

-Burning of vegetation

 

-Soil erosion

 

-Complete harvesting of crops

 

-deforestation

 

-Landslides

 

(Each 1/2mk, maximum 4 points)

 

 

 

1. Differentiate between alkaline and saline soils (3mks)

 

Answer:

-Alkaline soils are those whose soil water has a pH value of more than 7 (1mk)

 

-Saline soils are those that contain high levels of dissolved salts in the soil solution so as to affect the growth of most plants.

 

 

QUESTION 5

 

1. Briefly explain the relationship between percent base structure (PBS) and soil pH (3mks)

 

Answer:

-An increase in soil PBS results to an increase in soil pH (decrease in acidity)

 

-A decrease in PBS results to a decrease in soil pH.

 

-The pH decrease because the sites are occupied by the bases are taken up by hydrogen ions hence decreasing pH

 

 

1. Enumerate four effects of high acidity (low pH) in the soil (4mks)

 

Answer:

-Low pH results to reduced amount of calcium and magnesium available to the soil

 

-Low pH leads to high availability of Aluminium, Iron and other trace elements. This results to toxicity of the above elements.

-Low pH leads to fixing of phosphorous and potassium into insoluble forms hence lowering their availability.

 

-Low pH will affect growth of soil micro-organisms hence reducing their population.

 

 

 

 

 

1. Give five reasons why liming of soil is important (5mks)

 

Answer:

-To avoid toxicity of some elements

 

-To avoid deficiency of some elements

 

To add nutrients to the soil

 

-To create a conducive environment for soil micro-organisms

 

-To increase the percent base saturation of a soil

 

-To increase the cation exchange capacity of a soil

 

(Each 1mk, maximum 5 points)

 

 

1. List down the criteria used to determine whether an element is essential or not (3mks)

 

Answer:

-If the deficiency of an element causes a specific injury or growth abnormality then it is essential

 

-If the deficiency symptoms can be corrected by supplying that particular element and no other, then it is essential

 

-If the element is directly involved in metabolism in various plant species, then it is essential.

 

 

 

SS POOL 2

 

QUESTION 1

 

1. Define the following terms (4mks)

 

Answer:

1. i) Soil fertility (2mks)

Is the capacity of a soil to supply the required nutrients in the proper proportion for plant growth (1mk)

 

1. ii) Organic manure

Any substances organic in nature that when added to the soil they increase soil fertility

 

iii)Liming (1mk)

Is addition of compounds mainly of calcium and magnesium into the soil so as to correct unfavourable acidity conditions.

 

 

1. Using a diagram illustrate the organic matter cycle in a soil (5mks)

 

Answer:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Decomposition

 

 

 

1. Give three reasons why adding fertilizer to the soil is important in agriculture (3mks)

Answer:

-They supply required nutrients to plants

-Some add micro-organisms to the soil e.g organic manure

-They improve soil structure through formation of humus

-Some inorganic fertilizers aid in soil liming

-They improve water holding capacity of the soil e.g organic manure impart ‘spongy’ qualities to soil.

(each 1mk, maximum 3 points)

 

1. List the role played by phosphorous in plants (3mks)

Answer:

-Is a vital part of cell nucleus

-Essential for all cell division

-Involved in crop maturation

(Each 1mk, maximum 3 points)

 

QUESTION 2

1. Enumerate any three methods of inorganic fertilizer application (6mks)

Answer:

-Broadcasting

Fertilizer is spread uniformly over the field

 

-Top dressing

Fertilizer is applied on the soil surface after the crop has emerged and reached a certain stage

 

-Side dressing

Fertilizer placed along the side of the crop

 

-Band/row application

Applied in bands or row at a safe distance from the plant

 

-Drilling

Fertilizer applied together with the seeds during planting

 

-Folia spray

Fertilizer is mixed with water and then sprayed on crops.

 

-Drip application

Fertilizer is mixed with irrigation water used for drip irrigation.

 

(Stating 1mk, brief explanation 1mk, maximum 3 points)

 

 

 

1. List four differences between organic and inorganic fertilizers (4mks)

 

Answer:

-Inorganic fertilizers supply few elements while organic fertilizers supply several elements.

 

-Inorganic fertilizers are easy to handle and apply. Organic fertilizers are bulky and hence tedious in application.

 

-Inorganic fertilizers release elements fast. Organic fertilizers release elements slowly

 

-Inorganic fertilizers do not add organic matter to the soil. Organic fertilizers add organic matter to the soil.

 

-Inorganic fertilizers do not add beneficial micro-organisms to the soil. Organic fertilizers add beneficial micro-organisms.

 

-Inorganic fertilizers are expensive. Organic fertilizers are generally cheap.

 

-Inorganic fertilizers negatively affect the environment. Organic fertilizers modify the environment.

 

-The chemical composition of inorganic fertilizers is known. The composition of inorganic fertilizers is not known.

 

(Each 1mk, maximum 4 points)

 

 

 

1. Name four types of organic fertilizers (manures) (2mks)

 

Answer:

-Farmyard manure

 

-Compost manure

 

-Green manure

 

-Sewage sludge

 

-Mulches

 

(Each 1/2mk, maximum 4 points)

 

 

QUESTION 3

1. a) Explain three ways through which climatic factors assist in the process of weathering (6mks)

-Temperature

Variations cause expansion and contraction of rock materials hence breakages

 

-Wind

Removes any loose materials on rocks and carry them from one place to another.

 

-Water

Water in crevices solidifies and hence expands, exerting pressure which results to breakage of rocks.

Water absorbs rock materials hence softening it.

 

(Stating 1mk, Explanation 1mk, maximum 3 points)

 

 

b) Differentiate between a soil horizon and a soil profile (3mks)

 

-Soil horizon

Is a specific layer in the land area that is parallel to the soil surface and have physical properties different from other layers (2mks)

 

-Soil profile

Is sequence of arrangement of soil horizons (layer) from the top to the parent rock (1mk)

 

 

1. c) List four types of soil structures (2mks)

 

-Platty structures

 

-Blocky structures

 

-Prismatic structures

 

-Spheroidal structures (granular and crumb)

 

(Each 1/2mk, maximum 4 points)

 

 

1. d) Explain two importance of good soil structure (4mks)

 

1) Aeration

Good structure makes a soil well aerated

 

2) Water holding capacity

A good soil should have pore spaces for holding water.

 

3) Root penetration

A good structure should allow better root penetration

 

4) Seed emergence

A good structure should have pore spaces through which seeds emerge.

 

5) Ease of tillage

A good soil should have good workability i.e should not be too compact.

(Stating 1mk, explanation 1mk, maximum 2 points)

1. e) Name three soil management practices that enhance organic matter accumulation in the soil (3mks).

 

-Mulching

 

-Green manuring

 

-Application of fertilizer to promote growth of vegetation

 

-Minimum tillage

 

-Application of manures

 

-Incorporating crop and animal residues

 

(Each 1mk, maximum 3 points)

 

 

 

QUESTION 4

 

1. a) Differentiate between micro-pores and macro-pores (3mks)

 

Macro-pores

-Are found between peds

-Are usually filled with air and allow water to flow freely

 

Micro-pores

-Are found within the peds and hold capillary water.

 

 

1. b) Name any four factors that affect the rate of water infiltration into a soil (4mks)

 

i)Topography/slope

 

1. ii) Soil structure

 

1. ii) Impact of rainfall

 

1. iv) Organic matter content

 

1. v) Soil texture

 

1. vi) Cultivation practices

 

(each 1mk, maximum 4 points)

 

 

 

1. c) Explain the meaning of the following terms as used in soil water relations.

 

1. i) Field moisture capacity (FMC) (2mks)

-This is the point at which water in the macro-pores has drained down the soil.

-At the point the water in the soil is the one held in the micro-pores i.e capillary water.

 

1. ii) Permanent wilting point (PWP) (2mks)

-It is the point at which if water is continuously removed from, and not replaced, the plants wilt permanently

-Beyond this point no matter how much water is added to the soil, the plants will remain wilted.

 

 

1. d) List four types of soil water (4mks)

 

1. i) Capillary water

 

1. ii) Hygroscopic water

 

iii) Available water

 

1. iv) unavailable water

 

1. v) Superflow water

 

(Each 1mk, maximum 4 points)

 

 

QUESTION 5

 

1. a) Briefly explain how the following affect water holding capacity of a soil.

 

1. i) Organic matter (2mks)

-Organic matter breaks down to humus which will improve the structure of a soil and hence improved water holding capacity.

-Furthermore the humus formed will hold more water because of its ‘spongy’ nature.

 

1. ii) Soil texture (2mks)

-The finer the particles, the higher the water holding capacity of a soil and vise versa.

-This is because the small particles will provide a large surface area over which water will adhere.

 

 

b)List ways through which water is lost from the soil (2mks)                                                                                          

 

-Evapotranspiration

 

-Runoff

 

-Drainage to lower horizons

 

-Uptake and use by plants during photosynthesis.

 

-Surface evaporation.

 

(Each ½ mk, maximum 4 points)

 

 

1. c) List any six components of the soil organic matter (3mks)

 

Cellulose, hemicelluloses, lignin, fats, resins, sugars, starch, proteins, waxes, water, mineral elements.

 

(each ½ mk, maximum 6 points)

 

 

 

 

1. d) Briefly explain how the following causes an increase in soil acidity.

 

            1) Leaching/ water logging (2mks)

-Excess water drains down exchangeable bases to the lower horizons

-The sites vacated by the bases are occupied by hydrogen ions thus raising acidity.

 

            2) Cultivation/ growing of crops (2mks)

-Growing crops take up mostly cations (bases) e.g sodium, potassium etc ions

-The position of these ions are taken up by hydrogen hence increase in acidity.

 

 

1. e) Give four examples of liming materials (2mks)

 

Manures, fertilizers containing lime, limestone (CaCO₃), quick lime (CaO), slake lime, wood ash, basic slag, sugar, factory lime.

 

(Each ½ mk, maximum 4 points)

 

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