Plant Root System Contributions to Soil Carbon in Tilled Soils and Marginal Soils with Water Barriers.

Continuous supplies of plant-available water are often interrupted by anthropogenic modifications of the soil. Historically, soil tillage was a technological breakthrough for developing a good seedbed and to control weeds, plant diseases and insect pests. It was not until heavy and powerful equipment began to pull larger tillage tools across the landscape, did excessive tillage begin to become a menace to sustainable agricultural production. Irrigation of highly permeable soils has also become a liability to groundwater quality. Past research of subsurface water retention technology (SWRT) greatly reduced deep leaching resulting in water savings from 20 to 60% with yield increases from 50 to 400%. More recently, contoured engineered polyethylene membranes have been developed to extend the duration of plant-available water following rainfall and supplemental irrigation events. Contemporary modifications of SWRT maximize water retention in sandy soils without risking extended soil flooding. Additions of anaerobic mesosites within highly permeable soils add to the diversity among microbial communities of the soil rhizosphere. These diverse microbial communities are major contributors to improved aggregate stability, bioremediation of toxins and soil quality. Additional plant root exudates generated by more robust plants add to soil organic matter and modify soil greenhouse gases. Combinations of numerous abiotic factors, ie., gaseous composition, pH, microsite development through wetting/drying and freezing/thawing cycles, establish powerful synergistic biogeochemical interfaces which promote C sequestration and improved structure and function of the soil matrix. A recent review of soil biogeochemical interfaces by Totsche, et al (2010) emphasize the new challenges available in soil science as water holding capacities are engineered for the most hospitable water environment of plant rhizospheres. Current research emphasis is to install the best-engineered designs of water retention membranes into highly porous soils with the goal of improving the availability of water and nutrients for plant growth, controlling soil oxygen diffusion rates, modifying microbial communities which reduce emissions of greenhouse gases, and promote the biodegradation of pathogens and endocrine disrupting compounds before they contaminate groundwater supplies.