Determination of optimal N-fertilization rates, A',., for crop production that minimize risk of environmental degradation require accurate application of a response model. Several models are available to describe crop yield response to N fertilization. The objective of this work was to compare the relative accuracy of a quadratic, /{NQ), a modified Mitscherlich, and tanh(/V") models on 48 data sets. Data were collected from a Tara silt loam (fine-silty, mixed, frigid Pachic LJdic HaploboroU) over a 6-year period using two maize {Zea mays L.) hybrids and four tillage treatments, mouldboard plough, chisel plough, ridge tillage and no-tillage. In about one-third of the cases, all models performed about equally well. Generally, the tanh(jV) and modified Mitscherlich models gave better fit between N rate and grain yield data. The No,, ranged from about 140 to i 70 kg ha"' for the modified Mitscherlich model, 136 to 184 kg ha ' for the tanh(A') function, and 124 to f73 kg ha"' using the/^Aq) model. Estimated grain yields at these rates ranged between 6.58±1.30 to 7.59+1.69 Mg ha"' for the 90-day Minnesota maturity rated (MR) hybrid and between 7.52±2.40 to 8.72±1.70 Mg ha"' for the 95-day MR hybrid.