Wheat-Lolium multiflorum competence: effect of nitrogen application onto Argentinean varieties aggressivity

Abstract

The objective of this study was to establish the competitive ability of Argentinean wheat (Triticum aestivum L) varieties in competence with Lolium multiflorum, and to determine the nitrogen level influence in the competitive process. Fields experiments were conducted at the La Plata National University Experimental Station (34°S, 58°W) La Plata (Argentina) during 1997 and 1998. Two wheat varieties (Klein Cacique and Pro Inta Super) and a local ecotype of L. multiflorum were used. The aggressivity index for above dry matter and grain yield and relative yield total were used as a measure of competitive ability and complementary resources, respectively. The aggressivity index variation due varieties was significant (p<0.05) for above-dry matter at first node detectable of wheat in 1997. No effect of nitrogen fertilization was observed. Neither varieties nor nitrogen fertilization effects were registered at anthesis and maturity. At these crop stages, L.multiflorum had a higher aggressivity than K. Cacique and P. I. Super. Weed registered a higher aggressivity in 0 N2 and 100N2 for grain yield. A higher aggressivity of wheat varieties at first node detectable up to 100 pl.m−2 of weed was observed in 1998 for above-dry matter. Higher weed aggressivity than wheat varieties, irrespective of nitrogen application, were obtained at anthesis. There were no resources complementarity (RYT ∼ 1) and a complete competence amongst crop-weed association was detected. A higher weed relative growth rate from first node detectable stage could explain this reversion onto weed aggressivity index. The application of nitrogen would result in losses of wheat aggressivity and that these losses would increase with increasing L.multiflorum density.