Soil Properties and Testing Flashcards

When taking a composite soil sample from a 10-acre field, the standard recommendation is to collect at least:

Answer: 15–20 cores from random locations across the field

Collecting 15–20 random cores and mixing them into a composite sample provides a representative average of field variability.

Which of the following best describes 'apparent soil density' (bulk density)?

Answer: Mass of soil solids per unit volume of soil (including pores)

Bulk density is the dry mass of soil per unit total volume, including both solids and pore spaces.

Soil with a high sodium adsorption ratio (SAR) is considered 'sodic.' The primary agronomic problem with sodic soils is:

Answer: Dispersion of soil particles causing poor structure and permeability

High sodium causes clay particles to disperse, destroying soil aggregates and drastically reducing water infiltration.

For accurate nutrient recommendations, at what depth should samples typically be collected for routine agronomic crops?

Answer: 0–6 inches (or 0–8 inches depending on state)

Most state university recommendations for row crops are based on samples taken from the top 6–8 inches of soil.

Which laboratory measurement determines the soil's lime requirement more accurately than pH alone?

Answer: Buffer pH (e.g., SMP or Woodruff buffer)

Buffer pH tests measure soil buffering capacity so the lime requirement can be calibrated to the actual amount of acidity that must be neutralized.

Nitrate (NO₃⁻) moves through soil primarily by:

Answer: Mass flow with soil water (leaching)

Nitrate carries a negative charge and is not held by soil CEC sites, so it moves freely with soil water and is prone to leaching.

A soil test result shows 'low' sulfur (S). Which soil conditions most increase sulfur leaching risk?

Answer: Coarse-textured soils with high rainfall or irrigation

Sulfate (SO₄²⁻) leaches readily from sandy, low-organic-matter soils under high rainfall or irrigation conditions.