Effect of sowing date on winter wheat yields in Poland

The aim of this study was to evaluate the timeliness of winter wheat sowing on results obtained in practical production. The research material comprises results of farm surveys conducted in years 1986-2003 and 2008-2013. Yields obtained by sowing earlier than the date adopted as the optimum did not cause reduction in yields and in many cases were higher than those obtained by sowing in the optimal dates. Delayed sowings were a risk factor reducing yields significantly. After taking into account differences in technology the average yields, on fields sown after optimum sowing date were significantly lower in both analyzed periods, respectively 4,5% and 2,5%. The relatively high yields were obtained from some very late sown fields. It proves that use of appropriate agricultural technology and good forecrops allows to limit the decrease in yield due to late time of sowing