Nitrate potential from sludge and inorganic fertilizer in soil leachate beneath an irrigated agricultural field

Abstract

Two sets of continuous deep soil cores were removed from a 4 hectare field during the third year of crop treatment. Samples were removed once following sludge addition and once 6 weeks later following inorganic fertilizer application and a 30 cm pre-planting irrigation. A total of 504 soil samples were analyzed for soil texture, gravimetric moisture content, electrolytical conductivity, and pH, as well as concentrations of NO₃ , Cl⁻ , NO₂, and organic C. After three annual sludge applications, soil beneath plots amended with sludge, had higher average water-extractable NO3 concentration than plots amended with inorganic fertilizer. From one sampling date to the next, the field-averaged concentration of NO₃ increased from 282 mg 1⁻¹ to 335 mg 1⁻¹ . Results suggest a trend of increasing NO₃ in the vadose zone.