Nitrate-N and water movement in soil columns as influenced by tillage and corn residues

Laboratory soil columns, 0.3 m diameter x 0.7 m long, were used to study nitrate-nitrogen (NO3--N) leaching in sandy loam soil cropped to grain corn (Zea mays L,). Three tillage practices, no till (NT), reduced tillage (RT), and conventional tillage (CT), with residue (R) and without residue (NR), were studied. In Experiment 1, 30 min, 23.6 mm simulated rainfalls were applied at 0, 4, 60, 140 and 180 h. Before the 4 h simulated rainfall, granular calcium ammonium nitrate fertilizer was applied to the soil surface at a rate of 180 kg-N/ha. In Experiment II, using the same columns ten months later 30 min, 32.3 mm of simulated rainfall were applied at 6, 170, 312 and 412 h, after an initial soaking of the soil (0 h). Fertilizer was applied after 125 h, at the same rate as ii Experiment I, but in I L (14.4 mm) of solution. NO3--N leaching and moisture content were measured at 0.1, 0.2, 0.4, and 0.6 m depths. Drainage water flow only occurred in Experiment II. In Experiment I, higher nitrate nitrogen concentrations ([NO3--N]), occurred initially at 0.1 and 0.2 m depths in RT and CT, but less leached to lower soil depths. In the end, more NO3--N leached to 0.6 m depth in the NT treatment. In Experiment II, NO3--N leached to deeper layers (below 0.4 m) in RD and CT treatments. Conventional tillage exhibited the lowest drainage rates. Tillage and residue effects were statistically significant at the early stages of Experiment I (at 4 h and earlier), and at the later stages in Experiment II, at the 0.1 m depth (P < 0.05). Maximum soil MO3--N concentration occurred at 0.4 m depth in all treatments.