Fertilizer Sources and Application Flashcards

Which fertilizer source provides the most readily plant-available form of phosphorus?

Answer: Monoammonium phosphate (MAP)

MAP is a highly water-soluble, processed phosphate fertilizer where phosphorus is immediately available to plants, unlike rock phosphate which requires acidic conditions to dissolve slowly.

Variable rate technology (VRT) in fertilizer application is primarily driven by:

Answer: Grid or zone soil sampling data linked to GPS-controlled spreader controllers

VRT systems use geo-referenced soil sampling data (grid or management zones) to create prescription maps that direct GPS-controlled applicators to vary rates across the field.

What is the main disadvantage of broadcast phosphorus application compared to banded placement?

Answer: Broadcast P is more susceptible to fixation because it contacts more soil and fixing sites

Broadcasting phosphorus over the entire field surface exposes it to more soil fixing sites (Fe, Al, Ca), reducing availability compared to concentrating P in a narrow band.

When a nitrification inhibitor such as DCD (dicyandiamide) is used with ammonium fertilizers, what is the primary benefit?

Answer: It slows conversion of ammonium to nitrate, reducing leaching and denitrification losses

DCD inhibits Nitrosomonas bacteria, slowing nitrification and keeping N in the ammonium form longer, which is less susceptible to leaching and denitrification.

Which statement best describes the concept of 'luxury consumption' in plant nutrition?

Answer: Plants take up nutrients beyond their growth requirement when soil supply is abundant, without yield benefit

Luxury consumption occurs when plants absorb nutrients in excess of the amount needed for maximum growth, storing them in tissue without additional yield gains.

What critical factor determines whether to apply nitrogen in the fall versus spring for winter wheat production?

Answer: Risk of nitrate leaching or denitrification over winter based on drainage class and temperature

Fall N application risks loss over winter via leaching on well-drained soils or denitrification on poorly-drained soils; spring application synchronizes N with active crop uptake.

Which of the following best describes the 'cation exchange capacity' (CEC) concept as it relates to fertilizer management?

Answer: CEC indicates a soil's capacity to hold positively charged nutrient ions, influencing fertilizer rate and frequency decisions

CEC quantifies the soil's ability to retain cations like K+, Ca2+, Mg2+, and NH4+; soils with higher CEC can hold more nutrients and are less prone to leaching losses, affecting fertilizer timing and rates.