Grade 10 Agriculture – Properties of soil Quiz
1. Which soil particle is the largest in size?
Sand particles are the largest among the soil separates; silt and clay are much smaller, while loam is a mixture of particle sizes.
2. What soil property is described by the arrangement of soil particles into aggregates?
Soil structure refers to how individual particles bind together into aggregates (crumbs, blocks), affecting aeration and root growth.
3. Which soil colour often indicates high organic matter content in Kenyan topsoils?
Dark brown or black soils commonly contain more organic matter, which improves fertility and water retention in topsoil layers.
4. What does soil pH measure?
Soil pH shows how acidic or alkaline the soil is, which affects nutrient availability and suitability for crops like maize or tea.
5. Which soil type holds water well but drains slowly and can become waterlogged?
Clay has very fine particles and small pores, leading to high water-holding capacity but poor drainage and risk of waterlogging.
6. What is the term for the amount of pore space in soil that can hold air and water?
Porosity refers to the proportion of soil volume made up of pores that store air and water, important for root respiration and water movement.
7. Which practice increases organic matter content in Kenyan soils?
Applying compost or farmyard manure adds organic matter and nutrients, improving soil structure and fertility.
8. What does cation exchange capacity (CEC) indicate about a soil?
CEC measures how well soil particles (especially clay and organic matter) hold positively charged nutrient ions like calcium and potassium for plant use.
9. Which soil horizon is richest in organic matter and important for crop production?
The A horizon or topsoil contains most organic matter and nutrients and is where plant roots grow, making it crucial for crops.
10. What is soil tilth?
Tilth describes how workable the soil is and whether it has good crumb structure, aeration, and moisture for seed germination and roots.
11. Which test would a farmer use to estimate soil texture by feel in the field?
The ribbon test involves rolling moistened soil between fingers to form a ribbon and helps identify proportions of sand, silt, and clay by feel.
12. Which soil condition is most likely to cause poor root growth due to lack of oxygen?
Compaction reduces pore space and air supply to roots, limiting oxygen and leading to poor root development and crop yield.
13. What does bulk density of soil measure?
Bulk density is weight per unit volume and helps indicate compaction; high bulk density means fewer pores for roots and water.
14. Which soil property influences how quickly water moves down through the soil profile?
Permeability describes how easily water and air pass through the soil's pore spaces; sandy soils are highly permeable, clays are less so.
15. Which soil particle contributes most to nutrient holding capacity and CEC?
Clay particles have large surface area and negative charges that hold cations, increasing the soil's nutrient retention (CEC).
16. What is field capacity in relation to soil moisture?
Field capacity is the moisture remaining after gravity drainage; it represents the water plants can extract before soil becomes drier.
17. Which practice reduces soil erosion on Kenyan sloping farms?
Cover crops and contour farming slow runoff and hold soil in place, reducing erosion on slopes common in Kenya's highlands.
18. Which soil texture is best described as medium textured with a balance of sand, silt and clay, and generally good for crops?
Loam contains balanced proportions of sand, silt, and clay, offering good fertility, drainage, and workability for many crops.
19. Which factor most directly affects soil temperature near the surface?
Darker soils and those with more organic matter absorb and retain heat differently, affecting surface soil temperature important for seed germination.
20. What is soil salinity and why is it a problem for crops like maize?
Saline soils contain soluble salts that make it harder for plants to absorb water, causing stunted growth and lower yields.
21. Which soil layer contains partially decomposed organic material and is often dark and thin?
The O horizon is rich in organic residues (leaves, humus) and is often dark; on many farmed fields this layer is thin or mixed into the topsoil.
22. What effect does increasing organic matter have on sandy soils?
Adding organic matter to sandy soils helps bind particles, increase moisture and nutrient-holding capacity, and improve tilth.
23. Which measurement indicates the lowest water content at which a plant can no longer extract water and wilts permanently without recovery?
Permanent wilting point is the soil moisture level at which plants cannot recover turgor and continue to grow, important for irrigation planning.
24. Which soil condition encourages beneficial organisms like earthworms and improves root growth?
Healthy soils with good aeration and organic matter support earthworms and microbes that improve nutrient cycling and root development.
25. What is capillarity in soil science?
Capillarity is the upward movement of water through small pores by capillary action, which can supply moisture to plant roots above the water table.
26. Which property of soil is determined by the relative amounts of sand, silt and clay?
Soil texture is defined by the proportions of sand, silt and clay particles and affects water retention, drainage and root growth.
27. Which soil type is generally best for growing maize in Kenya because it holds moisture yet drains well?
Loam combines good water-holding capacity and drainage, providing a favourable seedbed and root environment for maize.
28. What is a common effect of very acidic soils (pH below about 5.5) on plant nutrients?
In strongly acidic soils aluminium can become soluble and toxic to roots, while phosphorus often binds to iron and aluminium and becomes less available to plants.
29. If a soil is dark brown or black, what does this most often indicate for Kenyan farm soils?
Dark colours in topsoil usually result from accumulated organic matter (humus), which improves fertility and moisture retention.
30. What does the term 'soil structure' mean?
Soil structure refers to how primary particles (sand, silt, clay) are grouped into peds or aggregates, affecting aeration, water movement and root penetration.
31. Which management practice is most likely to increase soil porosity on a smallholder farm?
Organic matter helps bind particles into stable aggregates and increases pore space, improving porosity for air and water movement.
32. Which soil texture allows water to drain fastest after heavy rains?
Sandy soils have large pores that let water move quickly, so they drain faster than silts, clays or loams.
33. What is meant by the term 'tilth' of soil?
Tilth describes physical conditions (structure, moisture, friability) that make soil suitable for planting and rooting.
34. Which is a major consequence of soil erosion on Kenyan farms?
Erosion removes the nutrient-rich topsoil (A horizon), reducing soil depth, fertility and the capacity to support crops.
35. What does cation exchange capacity (CEC) tell a farmer about their soil?
CEC measures the soil's ability to retain positively charged nutrient ions and make them available to plants; higher CEC often means better nutrient-holding capacity.
36. If a smallholder farmer wants to raise the pH of an acidic field, what is the recommended amendment?
Lime (calcium carbonate) neutralises excess acidity, raising pH and improving nutrient availability; fertiliser or salt will not correct low pH.
37. What characterises saline soils that reduce crop germination and growth?
Saline soils contain soluble salts that create osmotic stress for seeds and plants, reducing water uptake and causing poor germination and stunted growth.
38. Which soil layer typically contains the most plant-available nutrients and organic matter?
Topsoil accumulates organic matter, roots and microorganisms and is the zone where most nutrient cycling and plant uptake occur.
39. What does a high bulk density indicate about a soil?
High bulk density means more mass per unit volume (less pore space), which restricts root growth, water infiltration and aeration.
40. Which soil organism is particularly important for improving soil structure by making channels and mixing organic matter?
Earthworms burrow, create channels for air and water, and mix organic residues into soil, enhancing structure and fertility.
41. What does soil permeability refer to?
Permeability describes how quickly water can move down through soil pores; it's different from total water-holding capacity.
42. Which description fits loam soil?
Loam contains a mix of particle sizes that gives good structure, fertility, drainage and water retention—ideal for many crops.
43. What visible symptom is commonly caused by high soil salinity in crop plants?
Salinity causes osmotic stress and ion toxicity, often seen as leaf margin or tip burn, yellowing and reduced growth and yield.
44. Which farming practice helps reduce soil erosion on steep slopes in Kenya?
Contour methods and terraces slow water runoff, reduce soil loss and allow more water infiltration compared with ploughing up and down slopes.
45. Why is organic matter important for crop production on small farms?
Organic matter increases moisture retention, provides nutrients as it decomposes and helps form aggregates that improve aeration and root growth.
46. Which soil particle size is the smallest?
Clay particles are much smaller (<0.002 mm) than silt and sand, giving clay its high surface area and different physical behaviour.
47. How does soil compaction generally affect plant root growth?
Compaction reduces pore space and increases resistance to root growth, causing shallower roots and less oxygen for roots and microbes.
48. Which simple on-farm method is commonly used to check soil acidity if lab tests are not available?
Portable pH kits or meters give a practical measure of soil acidity in the field; colour or taste are unreliable and unsafe indicators.
49. If soil is very sticky and can be moulded when wet, which property does this indicate?
Clay particles cause soil to be sticky and plastic when wet because of their small size and surface forces binding particles together.
50. What is the main benefit of applying well-rotted compost to farm soils?
Compost adds humus and nutrients, enhances aggregation and water retention and supports beneficial soil organisms, improving overall soil fertility.