tilling, and applying nitrogen (table 1). Certain management practices can induce a temporary increase in soil respiration and can have a negative impact on SOM content. Table 1.—Interpreting management impacts on soil respiration and soil organic matter (SOM) Management practice Application Short-term impacts Long-term impacts Application of solid manure or organic material Apply at proper agronomic rate. Provides carbon and nitrogen to microbes, increasing their activity. Increased respiration when manure begins to break down; increased biomass/forage production. Improved soil structure; increased fertility and SOM content. Use of crops or cover crops in rotation Crops that have a high ratio of carbon to nitrogen (C:N) produce a high amount of biomass. Leave residue on soil surface to increase SOM. Temporary fixation of nitrogen during residue breakdown; increased soil moisture; decreased erosion. Improved soil quality; increased fertility and SOM content. Tillage, such as annual disking or plowing Mixes the soil, resulting in a temporary increase in oxygen and contact of residue to soil, allowing microbes to break down carbon sources. Released nitrogen and other nutrients and CO2; increased potential for erosion; increased rate of decomposition of residue and other carbon sources. Decreased SOM content, soil quality, and soil fertility; reduced diversity of soil (increased bacteria); damaged soil structure. Table 1.—Continued Management practice Application Short-term impacts Long-term impacts Use of crop residue Leave residue on the surface, increasing ground cover, to protect the soil. Nitrogen temporarily tied up during breakdown of residue; increased soil moisture; decreased risk of erosion; lowered soil temperature. Increased soil quality, fertility, and SOM. Application of nitrogen Provides nitrogen (energy), which allows microbes to break down Temporary increased respiration due to increased If properly managed, increased SOM and soil quality; increased
(0 to 1.0) (1.0 to 2.5) Green (2.5 to 3.5) (3.5 to 4.0) Yellow (4 to 5) Soil respiration activity* Very low Moderately low Medium Ideal Unusually high Dry, sandy soils that have little or no organic matter Soils with marginal biological activity and organic matter Soils that have a moderately balanced condition and to which organic matter has been added Soils with sufficient organic matter content and populations of active Soils with excessive organic matter content **Approximate level of CO2 – respiration <300 mg soil/week 300 to 500 mg CO2-C/kg soil/week 500 to 1000 mg CO2-C/kg soil/week 1,000 to 2,000 mg CO2-C/kg soil/week >2,000 mg soil/week <9.5 lbs 3 in/day 9.5 to 16 lbs in/day 16 to 32 lbs in/day 32 to 64 lbs in/day >64 lbs in/day Approximate quantity of nitrogen (N) release per year (normal climatic conditions) <10 lbs/acre 10 to 20 lbs/acre 20 to 40 lbs/acre 40 to 80 lbs/acre 80 to >160 lbs/acre * Under optimum soil temperature and moisture conditions. ** Doran, J., and W. Brinton. 2001. Soil quality correlation of basal respiration and N mineralization over time using intact 3-inch field soil cores under optimal temperature and moisture in the lab. U.S. Department of Agriculture, Agricultural Research Service. More accurate estimates of yearly potential mineralizable nitrogen (PMN) release with optimal re-wetting of air-dry soils can be made using the Solvita® soil CO2 burst test and calculator.