Effect of prolonged storage of soil lysimeters on nitrate leaching

Measurement of nitrate and nitrate leaching is important in environmental studies. Effect of soil storage on nitrate leaching was studied using Tokomaru silt loam soil. Four monolith lysimeters (230 mm i.d. × 250 mm long), and 12 small cores (25 mm i.d.) were collected from a sheep-grazed pasture near Palmerston North, New Zealand. Within 2 weeks of soil collection, two lysimeters (A, B) were leached. Subsamples of the small cores, and leachate samples were analyzed for nitrate. The remaining two lysimeters (C, D) and small cores were stored for 22 months at 3 ± 1°C, and the same experimental procedure then adopted. The mean soil solution nitrate concentrations in the 0-100; 100-200 and 200-250 mm layers were 14, 6 and 2 g N m^-3, respectively, before storage, and 320, 115, and 42 g N m^-3, respectively, after storage for 22 months. For lysimeters A and B, the initial nitrate concentrations in leachate were 2.5 and 4 g m^-3, and increased to peak concentrations of 5.5 and 6 g m^-3. However, initial nitrate concentrations in leachate for lysimeters C and D were 160 and 310 g m^-3. These "peaked" breakthrough curves for a resident nitrate seem to reflect non-uniform distribution of nitrate in the soil initially, and the preferential nature of water flow. This study showed that nitrification proceeded during low temperature storage, so storage of soil lysimeters should be avoided for nitrate leaching studies.