Soil Respiration Unit Soil Science Objectives O Define

Soil Respiration Unit: Soil Science

Objectives O Define: soil respiration and soil microbes O Explain the role of soil respiration in determining soil O O O 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

Soil Respiration 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).

Soil Respiration 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. O Soil microbes are responsible for soil respiration and may important soil processes. (bacteria, fungi, protozoa, algae) O One heaping table spoon of soil can contain over 9 billion microbes.

Soil Respiration Plants Water + Carbon Dioxide Sun Soil Food + Oxygen

Definitions 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 nitratenitrogen 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.

Definitions 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.

Factors Affecting Bulk Density: Climate O Cannot be changed O Affects temperature, moisture and indirectly affects biological activity

Factors Affecting Bulk Density: Biological Activity O Biological activity O Varies with the seasons and times of day

Factors Affecting Bulk Density: Soil Moisture 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 O 60% pore space saturation (field capacity) is ideal for respiration O Dry soils have low respiration rates because of less support for biological activities

Factors Affecting Bulk Density: Soil Organic Matter O Amount and quality of soil organic matter O Affects microbe activity

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

Managing Soil Respiration O Soil Respiration Management Practices O 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 O Use no-till practices. O Tilling practices decrease decomposition and accrual of organic matter O Minimize equipment use in fields O Minimize farm equipment use in general when soils are wet O Use designated locations for equipment traffic

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

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