Chapter 7

What is the role of soil organisms?

• Soil formation

  • mixers, creators of A horizon (humus)

  • modify soil to make it more favorable for their growth

  • Biological decomposition of rocks

What is mineralization in nutrient cycling?

What happens when more nitrogen is in the material being decomposed?

The more nitrogen in the material, the faster it will decompose

What happens to mineralization at different C:N ratios?

What is organic matter and what is it mostly made of?

What is humus and what is it mostly made of?

What factors affect soil organic matter and how does it affect it?

• Temperature- Cooler temperature limits humus degradation

• Moisture- Wetness inhibits humus breakdown

What are the largest carbon sinks?

• The deep ocean is the largest carbon sink

• Soil is the largest terrestrial carbon sink

What are the two types of decomposers in the soil? What can they do?

Synthesize and degrade humus

What types of plant residue exist and how does it affect decomposition?

• fresh, succulent: proteins, fats, waxes, high in nutrients (quick degradation)

• old, woody: cellulose, lignins, low in nutrients (slow degradation)

What environmental factors affect humus synthesis?

What are the characteristics and roles of microorganisms?

What are the characteristics of bacteria?

What are the characteristics of fungi?

What are the characteristics of actinomycetes?

What are the characteristics of protozoa?

What are the characteristics of algae?

What are the characteristics of myxomycetes?

What are the characteristics of mycorrhizae?

What is the biological soil crust made of?

• composed of fungi, lichens, cyanobacteria, bryophytes, and algae in varying proportions

What are the relationships between decomposition material, organisms, and nutrient composition?

What are management factors controlling organic matter?

What is productivity of soil?

• Capacity of land area to produce given crop at given level of management

What factors affect productivity?

• Slope Position- lower slopes tend to have more water, so there is more productivity

• Slope gradient/aspect- Steeper slopes tend to have shallow soils and they tend to be drier with high runoff

• Thickness of A- Deeper A= more humus and more rooting volume for water and nutrients

What is site index, and what affects site index?

• Site Index: Height of dominant trees of species at given age

• Site Index mostly related to thickness of A, capacity of plants to get water from B

What is cropland productivity, and what affects cropland productivity?

• Cropland Productivity- yield of given crop

• Yields often related to thickness of Ap, water-holding capacity of root zone

What are the relations between productivity and inputs?