104B State Water Resources Research Institute Scope 16: Water and Solute Movement in a Fragipan Soil as Modified by Ryegrass

Soils containing fragipan horizons occupy a significant land area in western Kentucky. These naturally occurring horizons are dense and often close to the soil surface, allowing them to alter water and nutrient distribution in a landscape. There is a need to explore management strategies to remediate shallow, fragipan horizons to promote storage of water. The work proposed here will investigate whether inclusion of a cover crop (ryegrass) can break up fragipan horizons and promote vertical movement of water and nutrients. Twelve intact soil cores (7.5 cm internal diameter) will be collected from a site containing a mixture of grasses mainly dominated by tall fescue located on the West Kentucky Research and Education Center at Princeton, KY. The soil type is a Zanesville silt loam (fine-silty, mixed, mesic, Typic Fragiudalf) which is forming in loess over acid sandstone residuum. Ports will be installed with depth in each soil core. Six soil cores will be seeded to annual ryegrass and the remaining cores will serve as controls. All cores will be incubated in the greenhouse for one growth cycle. Soil water content will be recorded daily in the ryegrass- and control soil cores using tensiometers connected to a data logger. Soil solution will be extracted through the installed ports with depth in all cores at 1 week, 2 weeks, 4 weeks, and 6 weeks of ryegrass growth. Several elements will be quantified ments (silica, aluminum, iron, manganese, nitrate, nitrite, ammonium) and dissolved organic carbon species will be quantified immediately. The purpose of following silica, aluminum, and iron is that they have been implicated in cementing the fragipan. The behavior of nitrate, nitrite, and ammonium will useful to assess from the standpoint of N cycling which is impacted by flow paths of water. After six weeks of growth, the ryegrass will be carefully clipped down to the soil surface. A solution of sodium bromide (NaBr) dissolved in Brilliant Blue FCF dye will be added to the soil surface of ryegrass-grown and control cores and leached until two pore volumes have leached through the columns. The bromide will serve as a non-reactive solute used to follow the movement of water. Brilliant Blue FCF dye will serve to illuminate areas of water flow paths in the soil. The cores will then be sacrificed and soil will be characterized with depth. Digital photographs will be collected and ImageJ will be used to estimate the area of dye-stained areas in ryegrass-treated soil and compared with the control. This fits in well with a goal of KWRRI, to promote conservation and management of water resources.