Exam 2 Flashcards
Which of the following forms of nitrogen CANNOT be taken up by the plant?
HMW dissolved organic nitrogen, N2, and NOx
Which of the following practices may cause a decline in SOM over time?
Ag activities: tillage (increases decompostition) and summer fallow (does not return plant matter to soil). As well, both increase erosion by breaking up soil structure and exposes SOM to wind/water.
Mineralization proceeds in the following 2 steps:
Organic to inorganic through aminization and ammonification (next step is nitrification)
Application of a crop residue with a C:N ratio of 60:1 will likely result in…
Nitrogen will be immobilized.
Processes that remove N from the soil system include:
Leaching of DON and NO3, denitrification to NO2, volatilization of NH4 to NH3 gas.
What increases ammonia volatilization losses?
Soils with a high pH (>9.3) and dry conditions/high temperatures (transfer of dissolved NH4 in soil solution to volatilization as NH3 gas)
Provide 2 reasons SOM is important for soil fertility
Supplies nutrients, formation of soil structure, improves water holding capacity, reduces erosion, supports microbes, buffer nutrients/pH/pollutants, stores carbon
Besides plant N uptake, 3 potential fates of ammonium in the N cycle are:
Volatilization, immobilization, and adsorption to clay
What two forms of sulfur are produced under anaerobic conditions?
Sulfur is primarily transformed into hydrogen sulfide (H₂S) and pyrite/iron sulfide (FeS₂).
Describe the nitrification process. List and briefly describe 3 factors that affect the nitrification process.
Starts with oxidation of ammonia to nitrite followed by oxidation of nitrite to nitrate by nitrifying bacteria. Affected by NH4 supply, pH levels, presence of O2, soil moisture and temp.
Describe how nitrogen is fixed biotically and abiotically:
Biotic: symbiotic and non-symbiotic fixation
Abiotic: Haber and lightening
What affects how much nitrogen is provided to subsequent crops?
The quantity of N2 fixed and the amount of residue returned. Can meet some needs of subsequent plants through mineralization of host residue.
Describe nitrogen losses and environmental consequences of losses?
Denitrification where nitrogen is lost as N2O as a gas (neg for GHG emissions), leaching of NO3 which causes groundwater pollution or eutrophication of nearby water bodies
What are the 4 Rs of nutrient management? Describe how they can be used to increase crop N uptake and reduce N losses.
Right source, rate, time, and place
- Fertilizers interact differently with other nutrients in soil, the right source can maximize these interactions (wrong source can impede efficiency).
- Application rate should match the requirements of the nutrient profile in the soil. Also consider soil/field variability.
- Timing can reduce nitrogen losses (leaching, denitrification, volatil) by increasing plant uptake.
- Placement of nutrients so that they are accessible to plants (reduces losses)
Ratio of SOM C to N
SOM is 50% organic carbon and 5% organic nitrogen
