Winter wheat agronomic traits and nitrate leaching under variable nitrogen fertilization

In the long-term field trial on an arable dystric Stagnosols, winter wheat (Triticum aestivum L.) grain yield, nitrogen use efficiency (NUE) and nitrate nitrogen (NO3--N) in lysimeter water were compared under treatments of 0, 100, 150, 200, 250 and 300 kg/ha of mineral nitrogen (N) during the growth years 1996/97, 1999/00, 2002/03 and 2005/06. Year properties significantly influenced N availability resulting in different responses of grain yield and NUE under variable treatments. Grain yield showed strong significant correlation with the rainfall accumulated from March to May (r = 0.77). In the case of a dry year 2003, winter wheat yield and NUE were adversely influenced by unfavourable climatic conditions. The optimal response of yield and NUE to increasing mineral N rates was found at the amount of 150-200 kg N/ha. Very strong significant correlation between the total amount of leached NO3--N and NUE was found for periods 1999/00 and 2005/06 where, in terms of increasing N levels, lower NUE conditioned higher NO3--N leaching (r = 0.91 and r = 0.94, respectively). According to the shallow depth of ground-water and installation of drainage systems, there is still a risk of freshwater contamination by nitrates if the N rates higher than 200 kg/ha were applied.