Tuesday, November 6, 2007
205-8
Nitrate Leaching in a Long-Term Experiment Under Supplementary Irrigation.
Virginia C. Aparicio, José L. Costa, and Martín S. Zamora. INTA, Ruta 226 km 73.5, Calle 21 # 772 1° A, Balcarce, 7620, Argentina
Applying high rates of N fertilizer to the crops has two major disadvantages, low fertilizer N use efficiency and loss of N by leaching, which may cause groundwater NO3 - pollution, especially in humid areas. The data generated in Argentina 2006 in Balcarce city, in Argentina 200 kg N ha-1) using UAN as the N source in 35 m2 plots. Corn (Zea mays L.) was planted every year and ceramic soil-water suction samplers were installed to depths of 1, 1.5 and 2 m . Drainage was estimated by the LEACH-W model. The N losses were analyzed using the PROC MIXED procedure as repeated measurements in time. LEACH-W model resulted in an appropriate tool in estimating water drainage in our soils, after calibration the model adjusted very well to the actual volume of water in the soil profile (R2 = 0.74). Losses of NO3-N during the period of the study increased as the rate of N applied increased. At all depths studied, significant statistical differences were found in favor of 200 N compared to 100 N and 0 N, and for 100 N compared to 0 N (P < 0.001). The nitrate leaching from non-fertilized soils occurred every year, and generally there was no difference between consecutive years for the depths studied. For 0 N, soil organic matter mineralization was the only N source which caused loss through leaching at a rate of 12 kg N ha-1 year-1 at 2 m depth. The greatest NO3-N losses through leaching occurred during crop growth. Significant differences (P<0.05) were obtained between cropping and fallow in the three treatments and depths studied for years 4 and 5; these two years produced the highest drainage volumes at all depths.