Soil Fertility and Analysis Flashcards
7 cards from real CCA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Soil Fertility and Analysis flashcards as text
Under which scenario is the potassium fertilizer recommendation most likely to be reduced or eliminated despite a medium soil test K level?
Answer: Fine-textured soils with very high CEC receiving regular manure or crop residue returns
On high-CEC fine-textured soils with regular manure or residue inputs, the K cycle is nearly closed and fertilizer K responses are rare even at medium test levels.
A grid soil sampling plan on a 10-acre grid collects one composite sample per 10 acres. What is the primary limitation of this approach compared to zone-based sampling?
Answer: It may mask within-grid nutrient variability, leading to over- or under-application in parts of each zone
A single composite per 10-acre grid averages out spatial variability within that area, potentially misrepresenting nutrient levels in high- or low-yielding sub-zones.
The Olsen sodium bicarbonate extraction method for phosphorus is preferred over Bray P-1 in soils where:
Answer: pH exceeds 7.0 and free carbonates are present
The alkaline Olsen method (0.5M NaHCO3, pH 8.5) is designed for calcareous and neutral-to-alkaline soils where acid-based extractants like Bray P-1 are neutralized by free lime.
Which nitrogen stabilizer technology works by inhibiting the soil enzyme urease, thereby slowing urea hydrolysis and reducing ammonia volatilization?
Answer: Urease inhibitors (e.g., NBPT)
NBPT (N-butyl thiophosphoric triamide) is a urease inhibitor that temporarily blocks the urease enzyme, delaying urea conversion to ammonium and reducing surface volatilization.
When tissue testing corn for nutrient sufficiency, which plant part and growth stage combination is considered the standard sampling protocol?
Answer: The ear leaf (leaf opposite and below the ear) at or near silking (VT–R1)
The ear leaf sampled at silking (VT–R1) is the universal standard for corn tissue testing because it reflects whole-plant nutrient status at peak demand.
Zinc deficiency in corn is most likely to occur under which field condition?
Answer: Cold, wet soils in early spring with high soil pH and low organic matter
Zinc availability decreases at high pH and in cold, wet conditions, and soils low in organic matter lack the chelating agents that keep Zn soluble — conditions common in early spring.
A CCA is advising on phosphorus management for a field adjacent to a lake. The most appropriate P index framework consideration in this context is:
Answer: Balancing agronomic P need against environmental P loss risk based on both soil P level and transport factors
Modern P index systems evaluate both the source component (soil test P level, fertilizer rate) and the transport component (slope, distance to water, runoff potential) to guide site-specific management that meets yield goals while protecting water quality.