Soil Fertility Quiz #10

Which of the following best describes why nutrient uptake timing is important relative to plant growth?

Nutrients must be available before the period of rapid growth to meet peak plant demand.

What process causes seedling injury when soluble fertilizer salts are placed in direct contact with the seed?

Plasmolysis

Which fertilizer listed below has the highest salt index?

Potassium chloride (0-0-60) — 116.2

Which of the following fertilizer placement methods places nutrients 2 inches to the side and 2 inches below the seed?

2×2 placement

Which of the following organic nutrient sources would release nitrogen most slowly over time?

Compost

What is the most important reason to inject or immediately incorporate liquid manure rather than leaving it on the soil surface?

Ammonium nitrogen in liquid manure is volatile and lost rapidly as ammonia gas when surface-applied.

Which factor most directly explains why organic nitrogen availability from manure is described as having a first-year availability that is less than total N?

A portion of manure N exists in organic forms that must be mineralized by soil microorganisms before plants can use it.

Which cover crop type is most appropriate for scavenging residual nitrogen after a manure application?

Grasses, because they have high nitrogen demand and efficient uptake

Why is sidedress application of immobile nutrients such as phosphorus and potassium generally NOT recommended for row crops?

Most row crops have already met their P and K demand by the time sidedress applications can be made.

A no-till corn producer in a humid region applies broadcast urea at 120 lb N/acre each spring before planting. Yield response has been lower than expected compared to a neighboring producer who sidedresses anhydrous ammonia. Which combination of loss pathways most likely explains the lower nitrogen recovery with the broadcast urea program?

Volatilization and immobilization, because surface residue creates conditions favorable for both NH₃ loss and microbial N tie-up

A producer has applied liquid swine manure at a nitrogen-based rate for eight consecutive years on the same fields near the confinement facility. Which long-term consequence is most likely to have developed in those fields compared to fields receiving no manure?

Phosphorus has accumulated well above crop removal rates, increasing the risk of nutrient runoff and water quality impairment.

Subsurface band-applied phosphorus consistently produces greater early-season growth responses in wheat than broadcast P at equivalent rates, particularly under no-till conditions. Which combination of mechanisms most fully explains this advantage?

Subsurface placement reduces fertilizer–soil contact, limiting P fixation, while simultaneously positioning P within the developing root zone where diffusion distances are short.

Increasing soil bulk density from 1.3 to 1.6 g/cm³ reduced total root length by approximately 75%. How does this degree of root restriction interact with fertilizer placement decisions to affect crop nitrogen recovery?

Severe root restriction limits the soil volume explored by roots, reducing the likelihood that roots will intersect fertilizer bands and diminishing the advantage of precision placement over broadcast application.

A cereal rye cover crop is terminated at heading stage rather than at the recommended early boot stage before corn planting. What nutrient cycling consequence is most likely to result from this late termination?

The mature rye residue will have a high C:N ratio, promoting microbial nitrogen immobilization that temporarily reduces plant-available nitrogen for the following corn crop.

A producer wants to apply a blended 7-21-7 starter fertilizer at 150 lb/acre to corn. The combined N + K₂O from this rate is 21 lb/acre. Based on this, which placement method would be required to apply this rate safely?

In a 2×2 band, because the combined N + K₂O of 21 lb/acre exceeds the safe limit for in-furrow and within-1-inch placement

A producer is evaluating whether to apply anhydrous ammonia via subsurface injection or surface broadcast urea for a split-applied nitrogen program in a high-surface-residue corn system. Beyond differences in cost and equipment, what are the two most agronomically significant factors that favor the subsurface injection approach?

Subsurface placement bypasses surface residue that promotes both immobilization of broadcast N and ammonia volatilization from urea hydrolysis, improving overall nitrogen recovery by the crop.

In comparing no-till and conventional tillage systems, no-till tends to produce shallower root systems in some soils despite better moisture retention. Which interacting set of factors most completely explains this apparent paradox?

No-till soils warm more slowly in spring and may have higher surface bulk density, limiting early root penetration depth even while retaining more moisture.

A producer transitioning from conventional tillage to no-till notices that starter fertilizer responses to phosphorus seem stronger in the first few years after the transition. Which explanation best accounts for this pattern?

No-till systems maintain cooler, wetter soils that reduce early-season P diffusion and root elongation, increasing the benefit of having P concentrated near the seed.

Nitrification essentially stops in a waterlogged field during a wet spring. Which condition is most directly responsible for this inhibition?

Oxygen depletion prevents aerobic nitrifying bacteria from functioning

Approximately how many pounds of nitrogen are mineralized per 1% of soil organic matter?

20 lbs N