Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 1, 2004
Publication Date: April 20, 2004
Citation: Suarez, D.L. 2004. Predicting soil and water chemistry in and below the root zone of agricultural lands: major ions, nutrients and toxic ions. U.S. Federal Interagency Workshop. pp. 93-96. Interpretive Summary: ARS has a responsibility to conduct research to maintain a productive soil environment for sustained crop production while minimizing or avoiding off-site degradation of soil and water resources. Computer models are essential tools for predicting the transport and fate of chemicals in the environment. This presentation provides a summary of ARS modeling activities and needs in the area of inorganic chemicals. It includes salts, nutrients, and potentially toxic ions and their transport in and below the root zone of agricultural soils. Major research activities consider prediction of salinity and ion composition in the root zone, including the processes of cation exchange, anion adsorption salt precipitation and dissolution, plant water and nutrient uptake, nitrogen transformations in the soil, and phosphorous fertilizer dissolution, adsorption, release and transport. Additional needs include bioavailability of heavy metals and their transport, especially in urban areas and as a consequence of historic application of lead arsenate as an insecticide on tree crops.
Technical Abstract: The focus of ARS research on inorganic chemicals centers around the need to maintain a productive soil environment for crop production while minimizing or avoiding off-site deg-radation of soil and water resources. The inorganic chemicals of interest are salts, nutrients and potentially toxic ions. Modeling is necessary for predict of the leaching of chemicals un-der existing practices and more importantly as a management tool to evaluate new practices. Evaluation of practices must, of course, consider not only chemical discharge but crop pro-ductivity and sustainability. The environment of primary interest is the soil root zone. In some instances groundwater and surface water processes and transport is also of interest. The root zone environment is a dynamic region of the soil with changing water content, plant uptake of water and chemicals, changing redox and gas phase composition and in many instances short residence times. Chemical modeling is highly dependent on an accurate description of water flow, thus a variably saturated water flow routine is often needed. Plant water uptake is an important component of water flow and determinant of solute composition (evapotranspiration concen-trates salts into the remaining soil water). In most instances chemical modeling in the root zone requires modeling of plant water uptake in response to environmental stresses (water, salts, ions, nutrients, and climate). Since the system is dynamic, predictions based on equilib-rium (thermodynamic) assumptions will usually not be satisfactory. Additional nutrients (NH4, PO4 and B), and toxic elements (Se, As, B, and Mo, as well as some heavy metals) are also the focus of ARS modeling research.