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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL RESOURCE EVALUATION OF MANAGEMENT SYSTEMS TO ENHANCE AGROECOSYSTEM SUSTAINABILITY

Location: Northern Great Plains Research Laboratory

Title: Microbial Engineering to Enhance Your Bottom Line

Author
item Nichols, Kristine

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 18, 2008
Publication Date: November 19, 2008
Citation: Nichols, K.A. 2008. Microbial Engineering to Enhance Your Bottom Line. Meeting Proceedings.

Interpretive Summary: The soil foodweb is a network of organisms where food in the form of biomolecules from one organism or the bodies of organisms is food for another organism. The foodweb starts with the carbon in leaves, shoots, roots, and root exudates. Each organism in the foodweb is trying to ensure its own survival by obtaining the most food at the least cost. This cost:benefit ratio requires organisms to manipulate or engineer their growing environment to position themselves close to their food source, their payment source, or both. The formation and stabilization of soil aggregates (i.e. soil pellets larger than 0.25 mm) is an example of a community of different microscopic organisms engineering their environment to increase their access to food and support greater growth on a macroscopic scale. The arbuscular mycorrhizal (AM) fungi which link soil/aggregate and plant together have bodies consisting primarily of microscopic threadlike strands that explore the soil/aggregates and grow into roots. These fine threads have a much greater surface area than roots and will contact more soil and absorb more nutrients from the soil than roots can. In addition, the hyphae form a ‘sticky-string bag’ in the soil which acts like a frame or net to collect partially decomposed leaves, shoots, and roots (i.e. particulate organic matter, POM) and primary particles (i.e. sand, silt, and clay) to begin aggregate formation. AM fungi also assist in making aggregates water stable. Water-stability means that the aggregate does not rupture following a precipitation event. Aggregates serve as miniature microbial towns which provide protection against predators, floods, and toxic chemicals and easy access to food sources, such as POM or other microbes. When the microbes in these towns consume their food, some of the excess nitrogen, phosphorus, and other nutrients are released in a plant-available form. The AM fungi transport these plant-available nutrients back to the roots as currency to pay for food (i.e. carbon) from the plant which the AM fungi use to make more hyphae. Soil aggregates improve water infiltration rates, water-holding capacity, aeration, root growth, nutrient cycling and resistance to water and wind erosion. To enhance microbial growth and improve soil quality, management systems need to incorporate reduced tillage, increase the quality and quantity of food entering the soil foodweb from the plant, and reduce synthetic fertilizer inputs.

Technical Abstract: The outer skin of Earth’s land masses is a thin veneer of living material (i.e. soil) which acts as a life-support system for all terrestrial life and is the most complex environment on earth with the greatest diversity of species. The billions of organisms in every handful of soil live in an interconnected foodweb, where every organism is both predator and prey. This combination of macroscopic – earthworms, insects, animals, and plants – and microscopic – bacteria, fungi, nematodes, micro-arthropods – organisms engineer an amazingly robust system to help agriculture meet the challenges of today and tomorrow. These challenges include rising fuel and input costs; increasing urbanization, global population, and pressures to be more environmentally sustainable; and decreasing water resources. Microbial growth assists macroscopic organisms in meeting these challenges by forming soil aggregates. In the soil matrix, the spatial distribution of soil aggregates creates large pores or channels which allow for more efficient air and water flow. Poor land management is the single greatest threat to microbial growth. The loss of plant cover and diversity, tillage, and high fertility inputs mechanically shear aggregates; expose buried organic matter, hyphal networks, and soil aggregates to rapid decomposition; and reduce the quantity and quality of food delivered to the soil foodweb. Reversing soil destruction is possible by changing land management to enhance microbial growth which improves plant productivity and the ability to produce more with fewer inputs to improve the economic bottom line.

Last Modified: 9/20/2014
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