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2007 Soil and Water Conservation Society - Soil Quality Workshop

"Soil Quality: the Foundation for Natural Resource Quality"

SOIL QUALITY AND WATER QUALITY

Dorcas H. Franklin
USDA-ARS, Watkinsville, GA
dory.frankln@ars.usda.gov

With six billion people now on the earth we must sustain productivity to provide sustenance for human life, housing, and fuels while protecting the environment for future generations. There are concerns over the environmental sustainability of the intensification of agricultural production and the coinciding intensification of agricultural fertilization. These concerns include: reduced biodiversity, pollution of ground water and eutrophication of rivers and lakes, and impacts on atmospheric constituents. A better understanding of agricultural ecosystems and nutrient management is imperative. Soil quality has often been shown to be an indicator of sustained productivity of both crop and grass systems. However, less work has been done which describes soil quality as an indicator of water quality. Rather, indicators of good soil quality (soil organic matter, soil phosphorus and nitrogen, pH, infiltration, cation exchange capacity, etc…) are often corollary measures in studies which have been done to determine effective management practices for good water quality. This talk will focus on the importance of specific management practices which have been shown to improve soil quality measures or indicators and the impacts of those management practices on water conservation. In this presentation water conservation will be used as an umbrella-term which describes both the ability of a management system to capture and retain water within the soil profile and the surrounding landscape (water quantity) and to act as a filter and reservoir for chemical and physical constituents which would be better assimilated by terrestrial plants and organisms than in the surrounding aquatic systems (water quality).

Conservation tillage practices have been increasingly adopted because they have been shown to create fewer environmental hazards. In these studies, conservation tillage has been shown to reduce erosion, increase infiltration of rain water and improve nutrient retention, all of which have been shown to improve productivity. However conservation tillage alone may result in higher than expected pesticide and nutrient losses unless additional measures are taken. Year-round vegetative cover on the surface of the soil whether as residue or growing vegetation must be better addressed. Depending on crop species and climatic factors, the amount of residues remaining on the soil surface after harvest and subsequent decomposition can vary, which influences soil erosion. Additionally, environments with good soil quality often have abundant soil fauna populations which can result in greater soil porosity. Some studies have suggested that this can result in excessive leaching of nitrate into groundwater while in other studies this has not been the case.

Overgrazing has been shown to compact soils and thereby increasing runoff and nutrient losses resulting in reduced livestock productivity. Depending on soil and landscape, impact of grazing management systems can range from beneficial to detrimental and should be considered in the design of management systems to improve soil quality. Generally speaking, the attenuation of water within the landscape often results in better utilization of that water and associated nutrients. The reduced likelihood of flash flooding is another measure of effectiveness of a management practice to attenuate water. An extreme example to illustrate this point is urbanization and the associated impermeable surfaces which often result in excessive runoff and reduced soil water storage.

Dory Franklin - Dory Franklin has work in conservation efforts mapping soils for SCS, characterizing soil and the morphology of preferential flow paths, and collecting and analyzing nutrients at the watershed scale. She currently contributes in the area of geography and soil geomorphology to improve understanding of impacts of land use, topography, soil geomorphology, soil chemistry, and hydrology on the movement of phosphorus and nitrogen through soils and across landscapes. She leads a multidisciplinary team of researchers, educators, and producers conducting on-farm research at the field and watershed scales to develop land management practices that reduce nutrient movement from farm fields into nearby streams and reservoirs. In recent years, Dr. Franklin was assigned as station representative to Team Conservation Tillage and has served as president of the Georgia Soil and Water Conservation Society.