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United States Department of Agriculture

Agricultural Research Service

Title: Glomalin - the Scummy Soil Builder

Author
item Nichols, Kristine

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2005
Publication Date: February 1, 2005
Citation: Nichols, K.A. 2005. Glomalin - The scummy soil builder. p. 5-9. IN: Kendall Heise (ed.) 27th Annual Zero Tillage and Winter Wheat Workshop. Proc. 1-2 Feb. Manitoba-North Dakota Zero-Tillage Farmers Association. Meeting Proceedings.

Interpretive Summary: Soil is a natural resource that increases the resiliency of production systems by improving nutrient cycling and water and air infiltration rates which increase production and reducing input costs. Billions of soil organisms - earthworms, insects, mites, bacteria, fungi, etc. - use organic matter and other carbon compounds to build soils. Soil organisms are related in a complex food web in converting organic matter into nutrients available to plants. Arbuscular mycorrhizal (AM) fungi are a group of soil organisms that are important in nutrient cycling and adding structure to soil. These organisms form a mutually beneficial relationship with most (about 80%) plants, including many crop plants. The body of AM fungi consists of hyphae or thread-like structures. These hyphae grow out of roots and several centimeters (or 1-2 inches) into the soil, or beyond nutrient depleted areas around plant roots, to deliver more nutrients to the root, especially immobile nutrients like phosphorus. In exchange for these nutrients, the plant provides the fungus with carbon in the form of simple sugars that the plant produces in abundance by photosynthesis. Numerous strands of AM hyphae form a net that entraps organic matter, clay, sand, silt, and other soil debris to form soil aggregates. Aggregates are glued together and 'protected' or stabilized by biomolecules, such as glomalin. Glomalin is produced by AM fungi to protect the hyphal 'pipeline' from nutrient loss. When released from hyphae, individual glomalin molecules will stick together to form a scum on the surface of the water. This scum will help to glue aggregates together while forming a protective PVC-like lattice on the surface of soil aggregates. Soil aggregates are important for many reasons including: 1. increasing the soil's stability against wind and water erosion, 2. maintaining soil pores, which provide air and water infiltration rates favorable for plant growth, 3. improving soil fertility by holding nutrients in protected micro-sites near the plant roots, and 4. increasing organic matter concentrations by protecting plant and root biomass from decomposition. Management practices, such as reduced or no tillage, continuous cropping, diverse rotations, reduced fertility inputs (especially P fertilizers), and minimum use of nonmycorrhizal crops such as canola, crambie, cabbage, broccoli, and cauliflower), increase aggregate stability and glomalin concentration.

Technical Abstract: Soils are a limited natural resource and are partially created by the activity of billions of organisms - earthworms, insects, mites, bacteria, fungi, etc. One important group of soil microorganisms are arbuscular mycorrhizal (AM) fungi. AM fungi form a mutually beneficial relationship with about 80% of vascular plants where fungal hyphae acquire nutrients from soil that are inaccessible to plant roots in exchange for photosynthetic carbon. Fungal hyphae form a net that entraps organic matter, clay, sand, silt, and other soil debris to form soil aggregates. These aggregates are glued together and stabilized by biomolecules, such as glomalin. Soil aggregation is important for: 1. increasing the soil's stability against erosion, 2. maintaining soil pores for air and water infiltration, 3. improving soil fertility, and 4. increasing organic matter concentrations. Reduced or no tillage, continuous cropping, diverse rotations, reduced fertility inputs (especially P fertilizers), and minimum use of nonmycorrhizal crops such as canola, crambie, cabbage, broccoli, and cauliflower) have positive impacts on the formation and stability of aggregates and increases in numbers of soil organisms and AM fungal hyphae concentrations.

Last Modified: 10/21/2014
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