manure application high C:N ratio residue quicker. Vehicle or farm equipment traffic Compacts soil decreasing pore space, water movement, oxygen for microbes and nitrogen loss from denitrification Management Practice Application Short Term Impacts Long Term Impacts Solid manure or organic material application Provide additional carbon and nitrogen source for microbes to breakdown and increase biomass production. Increased respiration when manure begins to breakdown and increased biomass production. Positive impact on soil structure, fertility and soil organic matter content. High residue crops or cover crops used in rotation with high C:N ratio High C:N ratio crops and added nitrogen increase decomposition and accrual of soil organic matter. 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. Tillage such as annual disking, plowing, etc. Stirs the soil providing a temporary increase in oxygen for microbes to break down carbon sources. 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. Declines in soil organic matter, soil quality, soil fertility. Crop residue management Leave residue on the surface increasing ground cover to protect the soil. Increased crop residue cover can tie up nitrogen temporarily in order to break down Positive impact on long term soil quality, fertility and soil organic matter content.
residue, increased soil moisture, decreased erosion and cooler soil temperatures. Nitrogen fertilizer or manure application 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. When managed correctly has an overall positive impact on soil organic matter and soil quality by increasing production levels and residue amounts. Vehicle or farm equipment traffic Compacts soil decreasing pore space, water movement, oxygen for microbes and nitrogen loss from denitrification. Decreases respiration, yields, water infiltration and increases runoff. Production declines, increased soil erosion and runoff, decreased soil quality, compacted soils and reduced microbial activity. Introduce each of the laboratory supplies to the students and review the laboratory processes and procedures with the class. See the guided notes lab for information. Students engage in the lab activity. Students record information and answer lab questions.
Table 2. Basic soil biological quality. Color/Colorimetric Number 0-1 Blue-Gray 1.0-2.5 Gray-Green 2.5-3.5 Green 3.5-4.0 Green-Yellow 4-5 Yellow Soil Respiration Activity Very Low Soil Activity Moderately Low Soil Activity Medium Soil Activity Ideal Soil Activity Unusually High Soil Activity Associated with dry sandy soils, and little or no organic matter Soil is marginal in terms of biological activity and organic matter Soil is in a moderately balanced condition and has been receiving organic matter additions Soil is well supplied with organic matter and has an active population of microorganisms High/Excessive organic matter additions *Approximate Level of CO2 - Respiration <300 mg CO2/kg soil/wk 300-500 mg CO2/kg soil/wk 500-1000 mg CO2/kg soil/wk 1000-2000 mg CO2/kg soil/wk >2000 mg CO2/kg soil/wk <9.5 lbs d 9.5-16 lbs 16-32 lbs 32-64 lbs >64 lbs d Approximate Quantity of Nitrogen (N) Release Per Year (Average Climate) <10 lbs/acre 10-20 lbs/acre 20-40 lbs/acre 40-80 lbs/acre 80->160 lbs/acre *Source: Doran, J. (2001) USDA-ARS Soil Quality Institute correlation of Solvita® and field soil respiration. Calculations based on a e-inch soil core (7.6 cm). Table 3. Soil respiration levels and interpretations. Sample Site Median 24-hr Soil or Start Time End Time Gel Color & Colorimetric Number Soil Activity Avg. Respiration Level lbs Quantity of N Released lbs/ac/yr