Nitrogen effect on competition between winter cereals and littleseed canarygrass.

Field experiments were conducted in northern Greece during 1994, 1995, and 1996 to study the effect of nitrogen fertilization on competition between littleseed canaryglass ( Phalaris minor Retz.) and wheat ( Triticum aestivum L.), barley ( Hordeum vulgare = distichum L.) or triticale ( Triticosecale). The presence of 400 P. minor plants per square meter until early March did not have an adverse effect on dry weight of any crop. However, their further presence significantly reduced dry weight of wheat and triticale, but not that of barley. Grain yield of wheat and triticale was reduced 48% and 47%, respectively, by season-long competition of P. minor, whereas the corresponding reduction for barley was only 8%. Crop yield reduction due to P. minor competition resulted mainly from reduction in ear number and less from reduction in 1000-grain weight. Nitrogen fertilization (150 kg N ha⁻¹), compared with control (0 kg N), slightly increased yield of all crops grown without weed competition. The same treatment also increased dry weight and competitive ability of P. minor against wheat and triticale, compared with that of control (0 kg N); the split application of nitrogen (50 kg N ha⁻¹ before crop sowing and 100 kg N ha⁻¹ in early March) caused a slightly greater increase in P. minor dry weight than did 150 kg N ha⁻¹ applied once before crop sowing. Dry weight of P. minor grown with barley was not affected by nitrogen fertilization, but it was severely reduced compared with that of P. minor grown with wheat or triticale. [ABSTRACT FROM AUTHOR]