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The responses of Hungarian-bred maize hybrids with different vegetation periods to sowing date, N fertiliser and plant density were studied in small-plot field experiments between 2002 and 2004. The maize grain yield was highest in the early and optimum sowing date treatments (8.563 and 8.325 t ha-1) and significantly less in the late and very late treatments (7.908 and 7.279 t ha-1). The year had a substantial effect on both the yield and the grain moisture content. In a long-term maize monoculture experiment set up in 1961, the N fertiliser responses of 6 maize hybrids with different vegetation periods were investigated. Averaged over the years 2002 and 2004 the maize grain yields in the N treatments were as follows (t ha-1): N0: 4.780, N80: 7.479, N160: 8.577, N240: 8.226. The grain yield and yield stability of maize were greatest at a N rate of 160 kg ha-1. The yield response was similar in both years, but the year had a considerable effect on the yield level. The N supplies to maize plants during the vegetation period could be well characterised using a SPAD 502 chlorophyll meter in the R3 phenological stage (18-22 days after silking). The plant density responses of maize hybrids were described by fitting a quadratic function to the data of 19-22 hybrids in the years 2002-2004. The optimum plant density averaged over the hybrids was between 67,483 and 70,161 plants ha-1. The maximum yield associated with optimum plant density was 7.978 t ha-1 in 2002, 6.60 t ha-1 in 2003 and 9.37 t ha-1 in 2004. The annual patterns of plant density responses for the maize hybrids exhibited considerable differences.

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