Soil Management Practice Questions

Correct answer: B. Less pore space, which can restrict roots and air and water flow

Bulk density is found by dividing a soil's dry weight by its volume, so it rises as traffic squeezes out pore space. High bulk density is a standard indicator of compaction and low porosity, conditions that can restrict root growth and slow the movement of air and water. Loose, organic-rich soils have lower bulk density, and trampling packs particles together without changing the soil's texture.

• A: Loose, organic-rich soils have lower bulk density, not higher.
• C: Foot traffic does not change soil texture; it packs the existing particles closer together.
• D: Traffic raises bulk density by packing the soil, which NRCS treats as a sign of compaction and impaired function, not of a livelier soil.

Source: Soil Quality Indicators: Bulk Density, USDA Natural Resources Conservation Service

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Correct answer: D. A clay loam rich in organic matter

CEC is a soil's capacity to hold positively charged nutrients such as calcium, magnesium and potassium on negatively charged surfaces, and those surfaces are mainly clay minerals and organic matter. CEC therefore rises with clay and organic matter content, so a clay loam rich in organic matter ranks highest. A silt loam is in the middle, and sands or gravelly soils have the lowest CEC.

• A: Sand grains carry little charge, so a sand low in organic matter has a very low CEC.
• B: Gravel and sand add almost no exchange sites.
• C: Silt loams have a moderate CEC, lower than a clay loam rich in organic matter.

Source: Calculating Cation Exchange Capacity, Base Saturation, and Calcium Saturation (ANR-81), Ohio State University Extension (CFAES)

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Correct answer: A. Burrows and casts add pores and stable aggregates, improving aeration and infiltration

Earthworms burrow and mix the soil, and the binding agents and casts they produce form new pores and stable aggregates, which improves tilth, aeration, infiltration and drainage. Roots often follow their burrows to nutrients in the casts. Nitrogen-fixing nodules are formed by bacteria, mycorrhizae are fungi, and earthworms feed on residues and soil rather than on living roots.

• B: Nitrogen-fixing nodules are formed by bacteria, not earthworms.
• C: Mycorrhizae are root–fungus partnerships; earthworms are not involved.
• D: Earthworms feed on organic residues and soil, not on living roots.

Source: Soil Quality Indicators: Earthworms, USDA Natural Resources Conservation Service

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Correct answer: A. Cement-based building debris mixed into the soil during construction

Urban soils often contain concrete, mortar and other cement-based materials left after construction, and these calcium carbonate-rich materials can raise soil pH well above that of nearby undisturbed soil. Acid rain and ammonium-based nitrogen fertilizers push pH down, not up, and decomposing leaf litter is not a usual cause of strongly alkaline soil.

• B: Acid rain would lower soil pH, not raise it.
• C: Nitrogen fertilizers tend to acidify soil over time.
• D: Decomposing leaf litter does not typically make a soil strongly alkaline.

Sources: Basics of Urban Soil Health (Technical Note No. 470-02, January 2024), USDA Natural Resources Conservation Service ; Soil pH and the Home Landscape or Garden (SL 256/SS480), UF/IFAS Extension

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Correct answer: B. Field capacity

Field capacity is the water a soil still holds after being saturated and then left to drain freely, usually over one to two days, once gravity has emptied the largest pores. Available water capacity is a different idea: the water held between field capacity and the permanent wilting point, the moisture level at which plants wilt and do not recover.

• A: At saturation all pores are filled; that is the starting point before free drainage.
• C: The permanent wilting point is the much drier level at which plants wilt and cannot recover.
• D: Available water capacity is the range between field capacity and the wilting point, not the water left after drainage.

Source: Soil Quality Indicators: Available Water Capacity, USDA Natural Resources Conservation Service

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Correct answer: D. The site is poorly drained; improve drainage or choose wet-tolerant species

In this perk test the hole is filled, allowed to drain, and refilled before timing. About 2 inches per hour is ideal and 1 to 3 inches per hour is acceptable, while a rate well below 1 inch per hour means the site is poorly drained, so drainage must be improved or species that tolerate waterlogged soil chosen. Three inches per hour is the top of the acceptable range, not a ceiling below which every rate passes.

• A: 1 to 3 inches per hour is the acceptable range; rates well below 1 inch per hour indicate poor drainage.
• B: Slow drainage means water lingers, the opposite of excessive drainage.
• C: Refilling the hole after the first fill drains is part of the method.

Sources: Soil Percolation: A Key to Survival of Landscape Plants (ID-237), University of Kentucky Cooperative Extension Service ; Soil Percolation: A Key to Survival of Landscape Plants (ID-237), University of Kentucky Cooperative Extension Service

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Correct answer: B. Soak deeply and infrequently, out past the drip line

Established trees should be watered deeply and infrequently: wet the soil to a depth of about 12 to 18 inches over the area from near the trunk out to a little past the drip line, then let the upper soil dry before watering again. UNL notes that most tree roots sit in the upper 18 inches of soil and can reach outward at least as far as the tree is tall, so water placed at the trunk or far below the roots is largely wasted. Light, frequent watering keeps a shallow layer saturated and ranks among the most common reasons trees die.

• A: Daily light watering keeps a shallow layer saturated and wets only a small area near the trunk.
• C: Most absorbing roots are in the upper soil and spread far from the trunk, so deep injection at the trunk misses them.
• D: Brief, frequent sprinkling wets only the surface and does not reach most of the tree's roots.

Sources: Efficient and Effective Tree Watering, University of Nebraska–Lincoln, UNL Water ; Efficient and Effective Tree Watering, University of Nebraska–Lincoln, UNL Water ; Efficient and Effective Tree Watering, University of Nebraska–Lincoln, UNL Water

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Correct answer: C. They release N gradually, so burn and leaching are less likely

Slow-release sources such as sulfur-coated urea, IBDU and resin-coated prills supply nitrogen gradually through the season, so the risk of burning roots is very low and less nitrogen is lost to leaching and runoff. Soluble sources such as urea and ammonium nitrate are the ones that green plants up quickly, but they do not stay in the soil for long and can burn plants if overapplied. Slow release describes how nitrogen is released, not how much the product contains.

• A: Slow release refers to how nitrogen is released, not to a higher nitrogen content.
• B: Quick green-up is a feature of soluble, fast-release nitrogen.
• D: Slow-release nitrogen is not a treatment for iron chlorosis.

Sources: Fertilizing Trees and Shrubs [fact sheet], University of New Hampshire Cooperative Extension ; Fertilizing Trees & Shrubs (HGIC 1000), Clemson Cooperative Extension, Home & Garden Information Center

Report a problem with this question · ID soil-022

Correct answer: A. Elemental sulfur

Elemental sulfur lowers soil pH because soil bacteria convert it to sulfuric acid, which neutralizes alkalinity; the effect is temporary and limited to the treated soil, and it cannot lower the pH permanently in soils that formed from limestone. Gypsum is the trap: it is a sulfate, but calcium sulfate does not acidify soil. Limestone and wood ash both raise pH.

• B: Gypsum (calcium sulfate) does not acidify soil.
• C: Limestone is a liming material that raises pH.
• D: Wood ash raises soil pH, and does so faster than limestone.

Sources: Soil pH and the Home Landscape or Garden (SL 256/SS480), UF/IFAS Extension ; Soil pH and the Home Landscape or Garden (SL 256/SS480), UF/IFAS Extension ; Fertilizing Trees and Shrubs [fact sheet], University of New Hampshire Cooperative Extension

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Correct answer: D. Surface chips won't starve the tree; reduced nitrogen is limited to the mulch-soil boundary

Studies show that woody mulch left on the soil surface increases nutrient levels in the soil and in plant foliage over time, and mulched plants do not develop nitrogen deficiency. WSU notes that the nitrogen shortage is confined to the boundary between mulch and soil, where it probably keeps weed seeds from germinating. Problems arise when wood is worked into the soil as an amendment, which should not be done, and fresh chips are actually recommended because they keep nutrients that composting would lose.

• A: Nitrogen depletion is limited to the mulch–soil boundary, not the whole root zone.
• B: Fresh chips are recommended because composting loses some of their nutrients.
• C: Wood mulch should not be incorporated into soil as an amendment.

Sources: Using Arborist Wood Chips as Landscape Mulch (FS160E), Washington State University Extension ; Using Arborist Wood Chips as Landscape Mulch (FS160E), Washington State University Extension ; Using Arborist Wood Chips as Landscape Mulch (FS160E), Washington State University Extension

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