Evaluating the Wheat (Triticum aestivum) Yield Loss Caused by Wild Oat (Avena fatua) Interference at Nitrogen Different Levels

Wild oat was described as a vigorously growing weed with a capability to attain greater height, and establish and develop extensive leaf area and horizontal branches when moisture and nutrients are not limiting. Fertilization is an important agronomic strategy used extensively to increase crop yield. Although, the effect of fertilizers is extensively investigated in wheat, there is little information to assess the effect of fertilizer application on wheat yield loss due to wild oat interference. The objective of this study was to investigate the wheat yield loss caused by wild oat interference at nitrogen different levels.
In order to evaluate the wheat yield loss caused by wild oat interference at different nitrogen levels, a field experiment was conducted at a farm in Ramhormoz city (latitude 31.16°N, longitude 49.36°E and 151 m asl), south-west of Iran in 2011-2012. The experiment was designed as a randomized complete block with a split plot arrangement with nitrogen fertilizer (N0: unfertilized control, N1: the use of 150 N Kg ha-1 before wheat seeding and N2: the use of 50 N Kg ha-1 before wheat seeding 100 N Kg ha-1 at late tillering stage of wheat) as the main plot and wild oat density (D0: weed- free control, D1: 25, D2: 50, D3: 75 and D4: 100 plants m-2) as the subplot with three replications.
A hyperbolic function was used to describe yield loss-density relationship. Increasing wild oat density had asymptotic-type effect on wheat yield loss. Initial slope (i) of the rectangular hyperbola model was a significantly greater when nitrogen fertilizer was applied. Moreover, for the rectangular hyperbola model, there was significant effect of nitrogen application on estimated maximum wheat yield loss (A). Application of 150 N Kg ha‑1 (N treatment) before crop seeding resulted in a greater competitive ability of wild oat than other treatments.
The results of this study suggest that the application of nitrogen fertilizer increases wild oat competitions when wheat fields infest with wild oat. Although the wheat yield loss was increased by N application, a such reduction was more recorded at N application than multistage-applied N. Greater knowledge of the effect of N on weeds and crop grown in competitive mixtures may allow a better understanding of why differences occurred among previous studies and aid development of fertilization strategies to reduce weed competition with crops.