Assessment of variability and monitoring methods for leaching under cover crop management

Graduation date: 1996The contamination of ground water resources represents a serious\ud problem and a prominent threat to the health of our society. This study\ud focuses on the leaching of inorganic anions as a function of agricultural\ud practices under natural field conditions. In order to enhance the\ud understanding of such leaching processes, this thesis evaluates the spatial\ud variability of the leaching characteristics of a site, the factors controlling\ud percolation, and the use of a cereal rye cover crop to reduce nitrate leaching.\ud Thirty-two Passive Capillary Wick Samplers (PCAPS) and 32 suction\ud cups were installed at a depth of 120 cm under row crop produced in a\ud Woodburn Variant loam (fine-loamy mixed mesic Aquultic Argixeroll).\ud Significant correlation for the water flux was seen at the 2.0 m distance,\ud beyond which values were uncorrelated. No spatial correlation was seen in\ud hydrodynamic dispersion coefficients. Percolation was independent of field saturated\ud hydraulic conductivity, while the quantity of incident water was\ud strongly correlated with percolation. The occurrence of preferential flow\ud affected the leaching process as documented by solute breakthrough ahead of\ud the main solute peak. Rates of nitrogen fertilizer application were\ud proportional to observed nitrate leaching losses. The cover crop significantly\ud reduced the amount of nitrate leaching at all N fertilizer application rates. At\ud the recommended rate, nitrate-N concentrations were lowered on average\ud from 22.2 to 9.9 mg/l; cumulative N mass losses were cut by 62% due to plant\ud uptake by the cover crop. The study demonstrated the importance of\ud conducting long-term field experiments under natural conditions to\ud accurately assess leaching processes