Soil fertility exam 3

What is the basic mass balance equation?

Inputs – Outputs = Change in Storage

What does it mean when a system is at "steady state"?

Inputs = Outputs; change in storage is 0

What is the formula for Mean Residence Time (MRT)?

MRT = Storage / Inputs (or Storage / Outputs)

What is the turnover rate in a box model?

Turnover rate = 1 / MRT

What does a box model ignore?

Internal processes within the system

What types of mass balance problems are commonly tested?

Simple mass balance, fertilizer rates, and total amount calculations

What type of system is a polluted ecosystem typically?

Not in steady state

What is ammonification?

Microbial transformation of organic N to NH₄⁺

What is nitrification?

Oxidation of NH₄⁺ to NO₃⁻ by chemoautotrophs

What is immobilization?

Uptake of inorganic N by microbes, converting it back to organic form

What is mineralization?

Transformation of organic nutrients into inorganic forms

Name at least 5 possible fates of NH₄⁺ in soil.

Microbial uptake, Plant uptake, Accumulation, Volatilization as NH₃, Oxidation to NO₃⁻, Stored on cation exchange sites, Fixation in clays, Incorporated into soil organic matter

Name at least 5 possible fates of NO₃⁻ in soil.

Microbial uptake, Plant uptake, Denitrification to gases, Leaching, Absorption on anion exchange sites, Storage in soil organic matter

What is net ammonification?

Change in NH₄⁺ pool size over time (NH₄ at time 2

What is net nitrification?

Change in NO₃⁻ pool size over time (NO₃ at time 2

Why does net nitrification increase at high N availability?

Chemoautotrophs face less competition, and immobilization decreases due to reduced microbial N demand

If litter C:N = 15, what do microbes do?

Mineralize nitrogen

If litter C:N = 30, what do microbes do?

Immobilize nitrogen from the soil

What is microbial growth efficiency in this context?

40% of carbon is used for growth; 60% is respired

How is the P cycle different from the N cycle?

P is not redox

What are the main forms of phosphorus in soil?

Primary (apatite), Secondary, Occluded, and Organic P

What affects phosphorus availability in soils?

Soil pH, parent material, pedogenesis, and ecosystem development

Why is phosphate not easily lost from soils?

It is the most preferred anion on positively charged soil surfaces

Before rock phosphate, what was a major source of phosphorus?

Guano (bird and bat excrement)

What is the concern with "Peak Phosphorus"?

The idea that global phosphorus resources may become depleted