Nitrate-N movement in a fine-textured vadose zone

ABSTRACT: Nitrate transport rates were measured in the fine-textured vadose zone of eight irrigated research plots fertilized at rates of O, 336 (300), and 448 kg N/ha (400 lbs N/ac). Five years earlier nitrate loading in the vadose zone of these plots was positively associated with a long-term history of N-fertilizer applications. Lag correlations between the 1985 and 1990 NO3-N data confirmed that NO3-N beneath four of the five fertilized plots moved as identifiable zones. The vertical transport rate of the NO3-N was ∼76 cm/yr (30 in/yr). These estimates compare favorably previously reported rates for fine-textured sediments from dryland fields Precipitation, which annually amounts to 66 cm/yr (26n/yr), appears to have been the driving force for the vertical NO3-N transport.