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LC Ag Science practice questions

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Question 1Scientific practices and experimental skills in agricultural science

A researcher wants to compare the mean fleece weight of two sheep breeds while removing the effect of age. Which statistical procedure is most appropriate?

  1. Simple linear regression of fleece weight on breed only
  2. A paired t-test between the two breed groups
  3. A chi-square test of independence on breed and fleece weight
  4. Analysis of covariance with age as a covariate Correct answer.

Explanation

Analysis of covariance adjusts the comparison of group means for a continuous covariate such as age, which is exactly the situation described. It partitions variation due to the covariate before testing the breed effect, giving a more precise and unbiased comparison.

Question 2Scientific practices and experimental skills in agricultural science

In a pasture trial, plots are arranged so that each treatment appears once in every block of four adjacent plots. What design is being used?

  1. Split-plot design
  2. Completely randomised design
  3. Systematic sampling design
  4. Randomised complete block design Correct answer.

Explanation

A randomised complete block design places every treatment exactly once within each block, and randomisation occurs within blocks. Blocking on adjacent plots controls spatial variation such as soil fertility gradients.

Question 3Scientific practices and experimental skills in agricultural science

A trial reports a treatment difference with a 95% confidence interval that excludes zero. What is the most defensible interpretation?

  1. The result proves the treatment works in all farm systems
  2. The treatment has no effect because the interval is narrow
  3. The sample size was too small to detect a difference
  4. There is evidence of a real treatment effect at the 5% significance level Correct answer.

Explanation

A 95% confidence interval that excludes zero is equivalent to rejecting the null hypothesis of no effect at the 5% level. It indicates a statistically detectable difference, though not necessarily a large or widely applicable one.

Question 4Scientific practices and experimental skills in agricultural science

Which measure of central tendency is most appropriate for describing the number of stillborn piglets per litter, a skewed count variable?

  1. Range
  2. Median Correct answer.
  3. Mean
  4. Standard deviation

Explanation

Count data with a skewed distribution are better summarised by the median because it is resistant to extreme values. The mean can be pulled upward by a few large litters, misrepresenting the typical litter.

Question 5Scientific practices and experimental skills in agricultural science

An agronomist measures soil nitrate at five depths in the same core. Which analysis respects the structure of these data?

  1. Repeated-measures or mixed-model analysis accounting for core Correct answer.
  2. Simple correlation between depth and nitrate ignoring core
  3. One-way ANOVA treating depth as independent groups
  4. Chi-square goodness-of-fit test on depth categories

Explanation

Measurements taken at multiple depths within one core are not independent, so the core must be modelled as a random or repeated factor. A mixed or repeated-measures model accounts for this correlation structure.

Question 6Scientific practices and experimental skills in agricultural science

A researcher wants to test whether a new fungicide reduces disease severity compared with an untreated control, with no interest in other treatments. Which is the most suitable analysis?

  1. Multiple regression with five predictors
  2. Three-way factorial ANOVA
  3. Cluster analysis of disease scores
  4. Two-sample comparison of mean severity scores Correct answer.

Explanation

With only two groups and a continuous response, a two-sample comparison such as an independent t-test or its nonparametric equivalent is appropriate. More complex models add no value when only one contrast is of interest.

Question 7Scientific practices and experimental skills in agricultural science

A field trial is replicated across three farms to represent a range of soil types. Which term best describes farms in this design?

  1. Fixed factor
  2. Nuisance covariate
  3. Random factor Correct answer.
  4. Blocking variable with no inference

Explanation

When sites are chosen to represent a broader population of environments, site is modelled as a random factor so results can be generalised beyond the sampled farms. This distinguishes it from a fixed factor whose specific levels are of direct interest.

Question 8Scientific practices and experimental skills in agricultural science

Which action best reduces the risk of measurement bias when assessing lameness scores in a trial?

  1. Using a single scoring occasion
  2. Informing the scorer which treatment each animal received
  3. Having the same observer score all animals Correct answer.
  4. Scoring animals in treatment order

Explanation

Keeping the same observer across all animals reduces between-observer variability, and where possible the observer should also be blinded to treatment. Consistency in scoring is central to reducing measurement bias.

Question 9Scientific practices and experimental skills in agricultural science

A trial reports a coefficient of variation of 22% for grain yield. What does this value indicate?

  1. The probability of a false positive is 22%
  2. The trial had 22% more plots than required
  3. The treatment means differ by 22%
  4. The standard deviation is 22% of the mean yield Correct answer.

Explanation

The coefficient of variation expresses the standard deviation as a percentage of the mean, allowing comparison of variability across trials with different mean yields. A value of 22% reflects the relative dispersion of the data.

Question 10Scientific practices and experimental skills in agricultural science

A researcher wants to estimate the average milk yield of a herd of 400 cows by sampling 40 animals. Which sampling method gives every cow an equal chance of selection?

  1. Choosing cows from one paddock only
  2. Simple random sampling from a numbered list Correct answer.
  3. Selecting cows with the highest previous yield
  4. Selecting the first 40 cows entering the shed

Explanation

Simple random sampling from a complete numbered list gives every animal an equal and independent chance of selection, which supports unbiased estimation. Other convenience or purposive methods introduce selection bias.

Question 11Scientific practices and experimental skills in agricultural science

Two treatments are compared on the same set of 12 ewes, with measurements taken before and after treatment. Which test is most appropriate for the mean change?

  1. Independent two-sample t-test
  2. Chi-square test
  3. Paired t-test Correct answer.
  4. One-way ANOVA with 12 groups

Explanation

When the same animals are measured twice, the observations are matched, so a paired t-test analyses the within-animal differences. This removes between-animal variation and increases power.

Question 12Scientific practices and experimental skills in agricultural science

A study finds a strong positive correlation between fertiliser applied and crop yield. Which conclusion is valid?

  1. No other factor can influence yield
  2. Higher fertiliser rates are associated with higher yields in these data Correct answer.
  3. Yield determines the amount of fertiliser applied
  4. Fertiliser application caused the yield increase

Explanation

Correlation quantifies the strength and direction of association but does not establish causation. Confounding factors such as soil fertility or rainfall could drive both variables, so only an association can be claimed.

Question 13Scientific practices and experimental skills in agricultural science

A researcher records the number of aphids per plant on a logarithmic scale before analysis. What is the main purpose of this transformation?

  1. To eliminate the need for randomisation
  2. To stabilise variance and approximate normality for count data Correct answer.
  3. To convert the response into a categorical variable
  4. To increase the number of replicates

Explanation

Log transformation compresses the influence of large counts, stabilising variance and making the distribution more symmetric, which better meets ANOVA assumptions. It does not alter replication or randomisation.

Question 14Scientific practices and experimental skills in agricultural science

A trial compares four fertiliser rates and finds a significant overall F-test. What should the researcher do next?

  1. Perform a post-hoc multiple comparison to identify which rates differ Correct answer.
  2. Repeat the trial until the result is non-significant
  3. Report only the overall mean
  4. Conclude all four rates differ from each other

Explanation

A significant overall F-test indicates that at least one treatment mean differs, but not which pairs differ. Post-hoc procedures with appropriate error control identify specific differences among the rates.

Question 15Scientific practices and experimental skills in agricultural science

Which practice most directly improves the external validity of an agricultural field trial?

  1. Reducing the number of replicates
  2. Testing treatments across a representative range of environments Correct answer.
  3. Increasing the number of measurements per plot
  4. Using a single highly controlled glasshouse

Explanation

External validity concerns whether results generalise beyond the study conditions, which is enhanced by testing across representative environments. This captures the range of soils, climates, and management systems to which findings should apply.

Question 16Scientific practices and experimental skills in agricultural science

A scientist wants to detect a 5% yield difference with 80% power at the 5% significance level. Which information is essential before the trial begins?

  1. The colour of plot markers
  2. The final treatment means
  3. The expected variability of yield in the trial Correct answer.
  4. The number of post-hoc tests

Explanation

Power analysis requires an estimate of variability, the effect size to detect, the significance level, and desired power to calculate the required replication. Expected variability is essential because it determines how many replicates are needed.

Question 17Scientific practices and experimental skills in agricultural science

Which statement correctly distinguishes accuracy from precision in a soil moisture sensor?

  1. Both terms describe the spread of repeated readings
  2. Precision requires a calibration curve whereas accuracy does not
  3. Accuracy is closeness to the true value; precision is consistency among repeated readings Correct answer.
  4. Accuracy is consistency among readings; precision is closeness to the true value

Explanation

Accuracy reflects how close a measurement is to the true value, while precision reflects how closely repeated measurements agree with each other. A sensor can be precise but inaccurate if it is systematically biased.

Question 18Scientific practices and experimental skills in agricultural science

A researcher records the proportion of germinated seeds from four seed lots, each sown in 10 trays. Which model is most appropriate for these data?

  1. Linear regression of proportion on tray number
  2. Principal component analysis of germination
  3. Paired t-test between seed lots
  4. Binomial generalised linear model with logit link Correct answer.

Explanation

Proportions based on a known number of trials per unit are appropriately modelled with a binomial generalised linear model, often using a logit link. This respects the bounded nature and variance structure of proportion data.

Question 19Scientific practices and experimental skills in agricultural science

In a split-plot field experiment, why are main-plot effects usually tested against a different error term from subplot effects?

  1. Because main plots are never replicated
  2. Because subplot data are always categorical
  3. Because subplots are measured only once
  4. Because main plots are larger and their randomisation is coarser Correct answer.

Explanation

Main plots are large and their randomisation units are whole plots, so the appropriate error term reflects whole-plot variation. Subplot effects are tested against the finer residual variation within main plots, which is why two error strata are used.

Question 20Scientific practices and experimental skills in agricultural science

Which action best supports reproducibility of a laboratory analysis for soil organic carbon?

  1. Reporting only the final mean value
  2. Recording the exact protocol, reagents, and calibration standards used Correct answer.
  3. Using a different analyst for every sample without records
  4. Changing the method between batches

Explanation

Reproducibility requires documenting the method in sufficient detail that another analyst can repeat it, including reagents, standards, and procedures. Transparent records are essential for verifying and repeating results.

Question 21Soils: formation, classification, physical, chemical and biological properties

In a soil profile, which horizon is typically the surface layer richest in accumulated organic matter?

  1. C horizon
  2. B horizon
  3. O/A horizon Correct answer.
  4. R horizon

Explanation

The uppermost horizons (O and A) receive litter fall and root inputs, so organic matter concentrates there and gives the dark colour of topsoil. Underlying horizons receive only material leached or translocated downward.

Question 22Soils: formation, classification, physical, chemical and biological properties

Which soil texture class generally has the greatest plant-available water-holding capacity?

  1. Silt loam Correct answer.
  2. Gravelly sandy loam
  3. Loamy sand
  4. Coarse sand

Explanation

Available water is held in the micropores that silt and clay create, so a medium-textured silt loam stores more plant-available water than coarse sandy textures. Sands drain rapidly and retain little water in the root zone.

Question 23Soils: formation, classification, physical, chemical and biological properties

A soil sample has a bulk density of 1.3 g/cm3 and a particle density of 2.6 g/cm3. What is its total porosity?

  1. 50 percent Correct answer.
  2. 65 percent
  3. 30 percent
  4. 80 percent

Explanation

Porosity equals one minus the ratio of bulk density to particle density, so 1 minus 1.3/2.6 equals 0.5, or 50 percent. This calculation assumes the standard particle density of about 2.6 g/cm3 for mineral soil.

Question 24Soils: formation, classification, physical, chemical and biological properties

Which soil-forming factor is described by the influence of climate on the rate of weathering and organic matter accumulation?

  1. Parent material
  2. Climate Correct answer.
  3. Time
  4. Topography

Explanation

Climate, especially temperature and precipitation, controls weathering intensity, leaching and biological production, so it drives the direction of soil development. The other factors modify or set limits on this process.

Question 25Soils: formation, classification, physical, chemical and biological properties

A soil has a pH of 5.0. Which statement best describes its likely condition?

  1. It is saline with high sodium adsorption.
  2. It is neutral and ideal for most crops.
  3. It is moderately acidic with increased aluminium solubility. Correct answer.
  4. It is strongly alkaline and dominated by carbonate.

Explanation

A pH of 5.0 is moderately acidic, and below about pH 5.5 exchangeable aluminium becomes soluble and can restrict root growth. Carbonate dominance occurs at high pH, and salinity is a separate measurement.

Question 26Soils: formation, classification, physical, chemical and biological properties

Which process most directly describes cation exchange in soil?

  1. Anions are held tightly by positive charges on organic matter
  2. Water molecules bind to clay and prevent ion movement
  3. Negatively charged clay surfaces release adsorbed cations into solution in exchange for others Correct answer.
  4. Microbes convert nitrate into ammonium

Explanation

Clay and humus carry net negative charge, so they adsorb cations that can be replaced by other cations from the soil solution. This exchange governs nutrient retention and buffering of pH.

Question 27Soils: formation, classification, physical, chemical and biological properties

A soil test reports a cation exchange capacity of 25 cmol(+)/kg and 80 percent base saturation. Which interpretation is most appropriate?

  1. The soil is sodic and requires gypsum application.
  2. The soil is highly acidic and needs heavy liming.
  3. The soil is well supplied with basic cations and is likely near neutral pH. Correct answer.
  4. The soil has very low nutrient retention and will leach readily.

Explanation

High base saturation means most exchange sites are occupied by calcium, magnesium, potassium and sodium rather than hydrogen and aluminium, which corresponds to a higher pH and good nutrient supply. A CEC of 25 cmol(+)/kg is moderately high, so nutrient retention is not poor.

Question 28Soils: formation, classification, physical, chemical and biological properties

Which group of soil organisms is most important for decomposing complex organic residues such as cellulose and lignin?

  1. Bacteria
  2. Fungi Correct answer.
  3. Nematodes
  4. Earthworms

Explanation

Fungi produce extracellular enzymes that break down complex polymers such as cellulose and lignin, which many bacteria cannot degrade efficiently. They dominate decomposition of woody and fibrous residues.

Question 29Soils: formation, classification, physical, chemical and biological properties

Which soil structure type is typically associated with good aeration and drainage in a well-managed agricultural topsoil?

  1. Platy
  2. Columnar
  3. Granular Correct answer.
  4. Massive

Explanation

Granular structure consists of small, rounded aggregates that create interconnected pores for air and water movement. It is characteristic of productive surface soils.

Question 30Soils: formation, classification, physical, chemical and biological properties

A farmer repeatedly cultivates a fine sandy loam when wet, and the surface becomes compacted and crusted. Which explanation best accounts for this?

  1. Earthworm activity increases and seals the surface
  2. Aggregates are destroyed by mechanical impact and dispersion, blocking pores Correct answer.
  3. Clay content rises through weathering during tillage
  4. Organic matter increases rapidly and binds the surface

Explanation

Wet tillage breaks aggregates and causes dispersion, so fine particles block pores and form a crust on drying. This reduces infiltration and can restrict seedling emergence.

Question 31Soils: formation, classification, physical, chemical and biological properties

Which soil order is characterised by soils that have formed in volcanic ash and have high water-holding capacity and variable charge?

  1. Histosols
  2. Andisols Correct answer.
  3. Gelisols
  4. Aridisols

Explanation

Andisols develop from volcanic ash and are dominated by short-range-order minerals with variable charge and high water retention. This distinguishes them from dry, organic or permafrost-affected soils.

Question 32Soils: formation, classification, physical, chemical and biological properties

In a soil classification key, a diagnostic subsurface horizon of clay accumulation is best described as which horizon?

  1. Argillic horizon Correct answer.
  2. Albic horizon
  3. Mollic epipedon
  4. Cambic horizon

Explanation

An argillic horizon is a subsurface layer with significant illuvial accumulation of clay. The name derives from the Latin for clay and is used as a diagnostic feature in classification.

Question 33Soils: formation, classification, physical, chemical and biological properties

Which property of a soil is most directly reduced by the addition of organic matter?

  1. Cation exchange capacity
  2. Bulk density Correct answer.
  3. Base saturation
  4. Particle density

Explanation

Organic matter lowers bulk density by increasing porosity and creating less dense aggregates. Particle density is largely fixed by mineral composition and changes little.

Question 34Soils: formation, classification, physical, chemical and biological properties

A soil has an exchangeable sodium percentage of 18 and a high pH with dispersed clay. Which amendment is most appropriate?

  1. Ammonium sulfate
  2. Limestone
  3. Gypsum Correct answer.
  4. Elemental sulfur

Explanation

Gypsum supplies calcium that displaces sodium from exchange sites, and the sodium can then be leached with water. This improves flocculation and structure in sodic soils.

Question 35Soils: formation, classification, physical, chemical and biological properties

Which statement correctly distinguishes soil texture from soil structure?

  1. Texture describes colour; structure describes the proportion of sand and clay
  2. Texture and structure both describe only the mineral composition of the soil
  3. Texture is the arrangement of aggregates; structure is the proportion of mineral particles
  4. Texture is the proportion of sand, silt and clay; structure is the arrangement of particles into aggregates Correct answer.

Explanation

Texture refers to the relative proportions of sand, silt and clay, which are fixed by the mineral fraction. Structure refers to how those particles are grouped into aggregates and is modifiable by management.

Question 36Soils: formation, classification, physical, chemical and biological properties

Which mechanism best explains why ammonium fertiliser acidifies soil over time?

  1. Nitrate is adsorbed onto negative sites
  2. Ammonium increases soil pH directly
  3. Ammonium reacts with clay to form carbonate
  4. Ammonium is taken up by plants and releases hydrogen ions Correct answer.

Explanation

When plants and microbes take up ammonium, they excrete hydrogen ions to maintain charge balance, and nitrification also releases hydrogen ions, lowering pH. This is why ammonium-based fertilisers are acidifying.

Question 37Soils: formation, classification, physical, chemical and biological properties

Which soil water term describes water held so tightly by soil particles that plants cannot extract it?

  1. Saturation
  2. Permanent wilting point Correct answer.
  3. Field capacity
  4. Gravitational water

Explanation

At permanent wilting point, water is held at high tension in very fine pores and by adsorption, so plant roots cannot extract enough to avoid wilting. The difference between field capacity and wilting point is plant-available water.

Question 38Soils: formation, classification, physical, chemical and biological properties

A soil is described as having a high buffering capacity for pH. Which property most directly explains this?

  1. Low organic matter and low surface area
  2. High cation exchange capacity and clay content Correct answer.
  3. High sand content and large pores
  4. High gravel content and rapid drainage

Explanation

Buffering arises from exchange sites and mineral surfaces that release or adsorb hydrogen and aluminium ions as pH changes. High CEC and clay content therefore resist rapid pH shifts.

Question 39Soils: formation, classification, physical, chemical and biological properties

Which biological process converts ammonium to nitrate in aerobic soil?

  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification Correct answer.
  4. Denitrification

Explanation

Nitrification is the two-step microbial oxidation of ammonium to nitrite and then nitrate, carried out by specialised bacteria and archaea under aerobic conditions. It supplies nitrate for plant uptake but leaves the nitrogen vulnerable to leaching.

Question 40Soils: formation, classification, physical, chemical and biological properties

A soil survey describes a soil formed on limestone with a high base saturation, high pH and little clay illuviation. Which parent material effect is most evident?

  1. The soil is dominated by organic peat accumulation
  2. The soil has been strongly affected by permafrost
  3. The soil has formed from granite under heavy leaching
  4. The calcareous parent material has limited acidification and weathering Correct answer.

Explanation

Calcareous parent material buffers pH and slows acidification, so base saturation stays high and clay translocation is limited. The soil reflects the chemistry of the underlying limestone rather than strong leaching.

Question 41Soils: formation, classification, physical, chemical and biological properties

Which practice most directly improves soil aggregate stability on a degraded cropland soil?

  1. Applying high rates of sodium-based fertiliser
  2. Removing crop residues and burning stubble
  3. Increasing cultivation frequency and bare fallowing
  4. Adding organic amendments and reducing tillage Correct answer.

Explanation

Organic matter acts as a binding agent that holds particles into stable aggregates, and reduced tillage preserves the hyphae and polysaccharides that bind them. Together these practices restore structure.

Question 42Soils: formation, classification, physical, chemical and biological properties

Which statement about soil organic carbon is most accurate?

  1. It consists mainly of fresh plant litter that persists unchanged for centuries
  2. It is highest in coarse sandy soils with low clay content
  3. It is largely derived from plant and microbial residues and is stabilised by association with minerals Correct answer.
  4. It is unaffected by temperature and moisture

Explanation

Soil organic carbon originates from plant, root and microbial inputs and is stabilised through association with clay and iron minerals and by aggregation. This mineral association slows decomposition.

Question 43Soils: formation, classification, physical, chemical and biological properties

A soil has a high clay content and a high plasticity index. Which engineering or agronomic implication is most likely?

  1. Poor drainage and susceptibility to compaction when wet Correct answer.
  2. Low cation exchange capacity
  3. High susceptibility to wind erosion
  4. Rapid infiltration and low water retention

Explanation

High-clay, plastic soils have small pores and swell when wet, so drainage is slow and the soil is easily compacted if worked moist. These properties also make them prone to structural damage.

Question 44Soils: formation, classification, physical, chemical and biological properties

Which factor most strongly limits biological activity in a cold, waterlogged peat soil?

  1. Low water-holding capacity
  2. Low oxygen availability and low temperature Correct answer.
  3. High pH and free carbonate
  4. Excess available phosphorus

Explanation

Waterlogging removes oxygen and slows aerobic decomposition, while low temperature further reduces microbial activity. Together these conditions allow organic matter to accumulate as peat.

Question 45Soils: formation, classification, physical, chemical and biological properties

Which statement best explains why a fine-textured soil holds more water at field capacity than a coarse-textured soil?

  1. Clay particles repel water and prevent drainage
  2. Coarse particles have higher surface area and adsorb more water
  3. Fine-textured soils have larger pores that trap water
  4. Smaller pores create greater capillary and adsorptive forces that retain water Correct answer.

Explanation

Fine-textured soils contain more micropores, and narrow pores exert stronger capillary and adsorptive forces that hold water against drainage. Coarse soils have large pores that drain readily.

Question 46Soils: formation, classification, physical, chemical and biological properties

Which primary mineral is most resistant to chemical weathering in warm, humid soils, and therefore tends to concentrate in the sand fraction as other minerals break down?

  1. Quartz Correct answer.
  2. Olivine
  3. Calcite
  4. Biotite mica

Explanation

Quartz is a framework silicate with strong silicon-oxygen bonds and no cleavage planes that admit water easily, so it dissolves very slowly even under intense leaching. Calcite, biotite and olivine all weather comparatively rapidly, so quartz persists and accumulates as the residual sand in strongly weathered profiles.

Question 47Soils: formation, classification, physical, chemical and biological properties

In a soil profile, which horizon is defined by the accumulation of illuvial organic matter and, commonly, iron and aluminium oxides leached from overlying layers?

  1. A C horizon of weathered parent material
  2. An O horizon of fresh litter
  3. A B horizon enriched by illuviation Correct answer.
  4. An E horizon depleted of clay and iron

Explanation

The B horizon is the zone of illuviation, where materials translocated downward from above are deposited, including organic matter, clay, and iron or aluminium oxides. An E horizon is the complementary zone of eluviation or loss, which is the opposite process.

Question 48Soils: formation, classification, physical, chemical and biological properties

A clay loam has a bulk density of 1.35 g/cm3 and a particle density of 2.65 g/cm3. Which total porosity does this correspond to?

  1. About 49 percent Correct answer.
  2. About 65 percent
  3. About 35 percent
  4. About 51 percent

Explanation

Total porosity equals one minus the ratio of bulk density to particle density, so 1 minus (1.35 divided by 2.65) gives about 0.49, or roughly 49 percent. This reflects the pore space not occupied by solid particles.

Question 49Soils: formation, classification, physical, chemical and biological properties

Why does adding lime raise the pH of an acidic soil far less than a simple neutralisation calculation would predict when the soil has a high cation exchange capacity and high reserve acidity?

  1. Exchangeable aluminium and hydrogen on the colloid surfaces must be neutralised before pH rises appreciably Correct answer.
  2. Lime is insoluble in soil water and reacts only with the solid mineral fraction
  3. Carbonates are rapidly leached from the surface before they can react
  4. The cation exchange capacity falls sharply as pH increases, consuming the added base

Explanation

Soils carry reserve or exchangeable acidity held on clay and organic colloids; added base must neutralise this pool, including exchangeable aluminium, before the soil solution pH shifts substantially. This is why high-buffering soils require much larger lime applications to achieve a target pH.

Question 50Soils: formation, classification, physical, chemical and biological properties

A soil has a high proportion of smectite-type 2:1 clay and is irrigated with water low in electrolytes. Which combination of behaviour is most consistent with this mineralogy?

  1. Low shrink-swell potential and stable aggregation under irrigation
  2. High shrink-swell potential and susceptibility to dispersion and crusting Correct answer.
  3. Low cation exchange capacity and weak retention of applied potassium
  4. High hydraulic conductivity maintained after wetting and drying cycles

Explanation

Smectite has a large internal surface and expanding interlayers, giving strong swelling on wetting and shrinkage with cracking on drying. When the soil solution is dilute, the diffuse double layer expands and aggregates disperse, promoting surface sealing and crusting.