Nitrate leaching from residual fertilizer N after spring thaw in two corn agro-ecosystems

Water samples at zero tension were collected using an open-ended lysimeter and analyzed for NO3--N from a Chicot sandy clay loam and a Ste. Rosalie clay soil under continuous corn (Zea mays L.) in 1993 and 1994, shortly after spring thaw. There was negligible leaching of NO3--N at previous fertilizer N rates of 0 and 170 kg ha(-1) in both soils. However, NO3--N concentrations of the leachates from soils receiving 285 and 400 kg N ha(-1) yr(-1) varied from 1.4 to 80 mg L-1, depending on the initial levels of soil residual NO3--N and the supply of percolation water. When the initial levels of soil NO3--N were relatively high and percolation of water was relatively slow in 1993, NO3--N concentrations of the leachates ranged from 20 to 80 mg L-1. Nitrite-N concentrations were from 1.4 to 15.6 mg L-1 when the initial levels of soil residual NO3--N were relatively low and percolation was relatively fast in 1994. The occasional higher NO3--N concentrations in the leachate from the previous higher N applications indicated a potential for contaminating surface and ground waters as a result of NO3--N leaching in the early spring.