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Soil Health-Aggregate Stability(West US)--Elbert County,Colorado,Western Part <br /> Soil Health - Aggregate Stability (West US) <br /> Definition of What is Estimated <br /> Aggregate stability is defined as the stability of macroaggregates(1-2 mm in <br /> size)against flowing water and is expressed as percent stable aggregates of the <br /> less than 2mm fraction. It is estimated from the organic matter content, total clay, <br /> and sodium adsorption ratio. Aggregate stability values are provided for horizons <br /> within the upper 6 inches, but not for sandy and organic surface layers. <br /> Significance <br /> Soil aggregate stability is an important soil property affecting soil health and crop <br /> production. It is important for stabilizing soil structure, increasing water infiltration, <br /> and reducing erosion. <br /> Soil aggregates are the smallest unit of soil structure. They are composed of <br /> decaying particulate organic matter, clay particles, microbial products, and fine <br /> roots.Aggregates are generally divided into macroaggregates (greater than 250 <br /> pm)and microaggregates (less than 250 pm). The size, strength, and stability of <br /> aggregates depend upon the stabilizing agents involved. They can be classified <br /> as temporary, transient, or persistent. Improved aggregate stability leads to <br /> increased water infiltration and storage in the profile, reduced erosion, and soil <br /> structure that is resistant to compaction. Increases in soil organic carbon <br /> improves aggregation and aggregate stability,which protect carbon compounds <br /> enmeshed in the aggregates from decomposition, leading to carbon <br /> sequestration. <br /> Factors Affecting Soil Aggregation and Aggregate Stability <br /> Inherent Factors-Microaggregation is generally considered to be an inherent <br /> property of the soil. Persistent binding agents include highly decomposed, high <br /> molecular weight organic materials(e.g., humic compounds), polymers, and <br /> polyvalent cations (e.g., calcium, aluminum, iron)that have a heterogeneous, <br /> non-specific structure. These agents are associated with microaggregation as <br /> well as soil organic carbon (SOC)sequestration. These persistent compounds <br /> are found in the interior of aggregates,forming organo-mineral complexes via the <br /> polyvalent cations. These agents are long-lasting, and the degree of aggregation <br /> formed by them is considered part of the inherent soil properties. Generally, <br /> management does not impact soil microaggregation. Soils naturally high in clay <br /> and polyvalent cations are likely to form more microaggregates. <br /> Dynamic Factors-Transient binding agents consist mainly of complex <br /> carbohydrates, or polysaccharides, and organic mucilages.As plant residues and <br /> compounds extruded by plant roots decompose, bacteria release mucilages that <br /> are complex carbon-rich carbohydrates. These carbohydrates serve as binding <br /> agents, or"glues,"to which clay particles can be adsorbed and bound together. <br /> The polysaccharides are non-humic compounds of high molecular weight and <br /> comprise about 20 to 25% of the soil humus. They are critical for binding <br /> microaggregates together, via polymer and polyvalent cation bridges,to form <br /> larger macroaggregates. Although binding with clay particles does provide some <br /> protection against decomposition,these binding agents generally decompose <br /> within a few weeks and need to be continually renewed through actively growing <br /> plants, decaying residues, or organic amendments. <br /> USDA Natural Resources Web Soil Survey 3/12/2018 <br /> AWN Conservation Service National Cooperative Soil Survey Page 1 of 4 <br />