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Soil Health-Aggregate Stability(West US)--Elbert County,Colorado,Western Part <br /> Temporary binding agents consist of plant roots, especially fine roots and root <br /> hairs,fungal hyphae, and bacterial and algal cells. These agents develop along <br /> with plant roots,forming a network that entangles mineral particles,through <br /> adsorption,to form macroaggregates.As roots cease to grow,the amount of <br /> these temporary agents is reduced. Planting cover crops or perennial plants <br /> maintains living roots longer in the soil,thus maintaining and strengthening the <br /> aggregates. Tillage reduces the amount of roots and the microbial biomass, <br /> especially in the surface horizon. <br /> Consequences of Weak Aggregates <br /> The first step in erosion is the breakdown of surface aggregates.Aggregates at <br /> the soil surface are weakened if the binding agents degrade at rates exceeding <br /> replenishment rates.These aggregates can be broken apart by outside forces,of <br /> which raindrops, wind, and tillage are among the most important. Changes in soil <br /> chemistry, such as increased sodicity of the soil, can also contribute to aggregate <br /> breakdown. As aggregates are broken down, the component particles clog the <br /> surface pores and surface sealing and crusting follow. This process results in <br /> reduced water infiltration, ponding, increased runoff and erosion, and sediment <br /> transport on and off site. Its occurrence can be minimized by strengthening <br /> aggregates. <br /> Additionally, reducing the size and strength of the aggregates throughout the <br /> profile weakens soil structure so that it is more easily compacted by field <br /> operations, especially if the soil is too wet. Poor structure can lead to ponding <br /> after rainstorms,which can result in increased evaporation and less water in the <br /> profile that might otherwise have been available for crop growth. <br /> Maintaining and increasing aggregation and aggregate strength can be <br /> accomplished through the implementation of soil health management systems. <br /> These systems may include reduced tillage operations(or preferably no tillage <br /> operations) and the incorporation of cover crops or a cash crop(such as winter <br /> wheat) into the rotation. Having crops and cover crops with varied rooting <br /> structures improves soil structure, as does maintaining living roots in the soil as <br /> long as possible. Studies have shown that plants will push into the rhizosphere, <br /> via the root system, about 20%of the carbon dioxide is fixed through <br /> photosynthesis.Those carbon compounds can support the soil microbial <br /> population,which is critical to soil structure,water infiltration, and nutrient cycling. <br /> Any management system that leads to increased soil organic carbon is likely to <br /> improve aggregate stability. <br /> Measuring Aggregate Stability <br /> Aggregate stability is determined by a wet sieving technique preceded by <br /> vacuum saturation of the 1-2 mm size aggregates as described in USDA-ARS <br /> (1966). Stable aggregates are corrected for sand greater than 0.25 mm as <br /> follows:Aggregate stability(%)= ((wt. of stable aggregates and sand)—(wt. of <br /> sand))/((wt. of sample)—(wt. of sand)). <br /> References <br /> Blanco-Canqui, H., and R. Lai. 2004. Mechanisms of carbon sequestration in soil <br /> aggregates. Criti. Rev. Plant Sci. 23:481-504. doi: 10.1080/07352680490886842 <br /> Cambardella, C.A., and E.T. Elliott. 1993. Carbon and nitrogen distribution in <br /> aggregates from cultivated and native grassland soils. Soil Sci. Soc.Am. J. <br /> 57:1071-1076. doi: 10.2136/sssaj1993.03615995005700040032x <br /> l Bien Natural Resources Web Soil Survey 3/12/2018 <br /> Conservation Service National Cooperative Soil Survey Page 2 of 4 <br />