Nitrate leaching in a clay loam soil after 44 years of consistent fertilization and crop rotation
Concerns about health and environmental effects of nitrate-contaminated water have made it imperative to estimate nitrate leaching losses through agricultural soils to groundwater. The objectives of this study were to establish the partitioning of the predicted water and nitrate leaching out of the root zone into tile-drainage and deep-drainage water, and to quantify baseline nitrate leaching from tile-drained plots on a Brookston clay loam soil (Orthic Humic Gleysol). Treatments included conventionally-tilled fertilized and non-fertilized continuous corn ('Zea mays L'.), continuous Kentucky bluegrass ('Poa pratensis L'.), and a corn-oats ('Avena sativa L'.)-alfalfa ('Medicago sativa L'.)-alfalfa rotation with each crop in the rotation grown every year. The fertilized plots received chemical fertilizer applications of 16.8 kg N ha-1, 67.2 kg P2O5ha-1, and 33.6 kg K 2O ha-1 annually. Corn also received 112.2 kg N ha-1 of side-dressed ammonium nitrate. LEACHN a sub-model of LEACHM (L_eaching E_stimation A_nd C_H_emistry M_odel) was used to predict total nitrate leaching at 70 cm depth in four selected plots. The cumulative nitrate losses (1999-2002) in tile drainage water were 131.6 kg N ha-1 for fertilized rotation corn and 79.7 kg N ha-1 for fertilized continuous corn. In contrast, cumulative nitrate losses in tile drainage were lower for non-fertilized bluegrass (4.4 kg N ha-1), fertilized bluegrass (6.6 kg N ha -1), and non-fertilized continuous corn (7.5 kg N ha -1). The LEACHN predicted cumulative (1999-2002) percentages of water and nitrate that were considered as deep-drainage in four plots were 59% water (597 mm) and 78% nitrate (156 kg NO3-N ha-1) in rotation fertilized treatment, 48% water (481 mm) and 58% nitrate (112 kg NO3-N ha-1) in continuous corn fertilized treatment, 40% water (405 mm) and 55% nitrate (31 kg NO3-N ha -1) in rotation non-fertilized treatment, and 60% water (326 mm) and 57% nitrate (10 kg NO3-N ha-1) in continuous corn non-fertilized treatment. Over 4-years, the predicted baseline nitrate leaching in the non-fertilized rotation plot (54.8 kg NO3-N ha-1) was 27% of that in the fertilized rotation plot (199.9 kg NO3-N ha -1), while in the non-fertilized continuous corn treatment (17.5 kg NO3-N ha-1) it was only 9% of that in the corresponding fertilized treatment (191.7 kg NO3-N ha-1 ).