Unit: Soil Science

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Define: soil respiration and soil microbes
Explain the role of soil respiration in determining soil health
Diagram the role of soil respiration in the cycle of life on earth
List and explain inherent factors that affect soil respiration
List and describe soil respiration management processes
Interpret management impacts on soil respiration and soil organic matter
Measure soil respiration and interpret data

O Soil respiration is a measure of the carbon dioxide released from the soil by microbes decomposing soil organic matter and from the respiration of plant roots.
O Soil respiration indicates soil health (soil organic matter content, soil organic matter decomposition and the level of microbial activity).

O Respiration rate can be based on the amount of soil organic matter present.
O Soil organic matter is a food source for microbes and when microbes are present and working, respiration is higher.
O When soil organic matter is absent or low, there is less decomposing activity.
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Soil microbes are responsible for soil respiration and may important soil processes. (bacteria, fungi, protozoa, algae)
One heaping table spoon of soil can contain over 9 billion microbes.

Water + Carbon Dioxide
Plants
Sun
Soil
Food + Oxygen

Ammonification: occurs in the nitrogen cycle when soil organisms decompose organic-nitrogen converting it to ammonia.
Available Water Holding Capacity: Soil moisture available for crop growth; also defined as the difference between field capacity and wilting point, typically shown in inches/foot.
Nitrification: Occurs in the nitrogen cycle when soil organisms convert ammonia and ammonium into nitrite and next to nitrate-nitrogen which is available to plants.
Bulk Density: Weight of dry soil per unit of volume, more compacted soil with less pore space will have a higher bulk density.

Denitrification: Conversion and loss of nitrate nitrogen as nitrogen gases when soil becomes saturated with water.
Respiration: Carbon dioxide release from soil from several sources
(decomposition of organic matter by soil microbes and respiration from roots).
Soil Porosity: Percent of total soil volume made up of pore space.
Soil Water Filled Pore Space: Percent of pore space filled with water.
Soil Water Content, Gravimetric: Weight of soil water per unit of dry soil weight.
Volumetric Water Content: Amount (weight or volume) of water in soil core by volume.

O Climate
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Cannot be changed
Affects temperature, moisture and indirectly affects biological activity

O Biological activity
O Varies with the seasons and times of day

O Soil moisture
O As moisture increases, respiration rates increase until the pores are overly saturated, resulting in lower oxygen content and lower soil organism respiration
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60% pore space saturation (field capacity) is ideal for respiration
Dry soils have low respiration rates because of less support for biological activities

O Amount and quality of soil organic matter
O Affects microbe activity

O Soil texture
O Clay – soil organic matter is “protected” from decomposition
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Sand – too little organic matter
Medium texture (silt and loam) – favorable for soil respiration

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Soil Respiration Management Practices
Leave crop residues on the soil surface.
O Residues with low C:N ratios decompose faster than those with high C:N ratios
O High residue crops + added Nitrogen = higher decomposition rates and accrual of organic matter
Use no-till practices.
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Tilling practices decrease decomposition and accrual of organic matter
Minimize equipment use in fields
Minimize farm equipment use in general when soils are wet
O Use designated locations for equipment traffic

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Use cover crops.
O Roots provide respiration
Add organic matter.
O Nourishes microbes
Irrigate dry soil.
O Added water boosts the quality of the environment for microbes and therefore boosts soil respiration
Drain wet soil.
O Too much water prevents microbes from being productive

Management Practice Application
Solid manure or organic material application
High residue crops or cover crops used in rotation with high C:N ratio
Tillage such as annual disking, plowing, etc.
Crop residue management
Nitrogen fertilizer or manure application
Vehicle or farm equipment traffic
Provide additional carbon and nitrogen source for microbes to breakdown and increase biomass production.
High C:N ratio crops and added nitrogen increase decomposition and accrual of soil organic matter.
Stirs the soil providing a temporary increase in oxygen for microbes to break down carbon sources.
Leave residue on the surface increasing ground cover to protect the soil.
Short Term Impacts
Increased respiration when manure begins to breakdown and increased biomass production.
Long Term Impacts
Positive impact on soil structure, fertility and soil organic matter content.
High C:N ratio crop residue tie up nitrogen temporarily in order to break down residue, increased soil moisture, decreased erosion.
Positive impact on long term soil quality, fertility and soil organic matter content.
Provides a flush of nitrogen, other nutrients and carbon dioxide release immediately after tillage.
Increases erosion rates, decomposition rate of residue, and other carbon sources.
Increased crop residue cover can tie up nitrogen temporarily in order to break down residue, increased soil moisture, decreased erosion and cooler soil temperatures.
Declines in soil organic matter, soil quality, soil fertility.
Positive impact on long term soil quality, fertility and soil organic matter content.
Provides nitrogen (energy) source for microbes to break down high C:N ratio residue quicker.
Temporary increase in respiration due to increased rate of breakdown of organic materials.
Compacts soil decreasing pore space, water movement, oxygen for microbes and nitrogen loss from denitrification.
Decreases respiration, yields, water infiltration and increases runoff.
When managed correctly has an overall positive impact on soil organic matter and soil quality by increasing production levels and residue amounts.
Production declines, increased soil erosion and runoff, decreased soil quality, compacted soils and reduced microbial activity.