Effects of Deficit Irrigation and Wild Oat (Avena ludoviciana) Density on Yield and Yield Components of Wheat

Water stress is one of the most important abiotic factors that restrict the growth and production of plants in the world, especially in arid and semi-arid regions. In Iran, a majority of wheat are located in arid and semi-arid regions. In these regions, drought stress occurs due to the lack of water which causes a considerable decrease in the yield of wheat. A suitable strategy to achieve satisfactory production in these areas is to apply deficient irrigation systems with the aim of improving water use efficiency and acceptable yield. Weed competition is another factor which decreases the wheat yield. Wild oat, due to its high compatibility and different ecological conditions, is one of the most important weed in wheat in most areas of Iran. Therefore, it is necessary to understand their behavior in the field, if we plan to apply appropriate weed management methods. Because any management change in the field may change weed behavior, and since the drip irrigation is spreading and the merits of deficit irrigation is known, it is necessary to evaluate their behavior at these conditions. Thus, the aim of this study was to study the wheat response to the interference of wild oat under deficit irrigation conditions. An experiment as split plot in randomized complete block design was conducted to evaluate the effects of deficit irrigation in three levels (supply of 100, 80 and 60 percent of crop water requirement as main plot) and wild oat density in four levels (0, 20, 40 and 80 plant m-2) on wheat yield in Shahrood agricultural research center. Wild oat seed was collected from wheat field around Shahrood and was planted with wheat. Crop water requirements calculated by Penman-Monteith equation amended by FAO. Irrigation treatments was applied at the beginning of jointing stage and continued during the growing season. At the end of experiment, two square meters of each plot harvested to measure the grain yield and biological yield. At this time 0.25 square meters of each plot harvested and yield components were measured. Data were analyzed in SAS software (version 9.1). Slicing method was used for interaction mean comparison. The effects of irrigation regime and wild oat density were significant on the number of spikes, the number of grains at spike, infertile tiller ratio, spike length, plant height, biological yield, grain yield, harvest index and water productivity. Decreasing the water usage to 60% of the water requirement decreased the grain yield and biological yield of wheat by 38.59 and 11.64%, respectively at the density of 80 bushes m2. Increasing the wild oat density up to 20 plants per m2 had no significant effect on the grain and biological yield of wheat, while increasing it up to 80 plants in the deficient irrigation regime with 60% of water requirement, decreased the grain and biological yield of wheat to 52.3 and 26.2%, respectively, compared with the control (100% of the water requirement) and zero density of wild oat treatment. Spike numbers per unit area showed a significant and positive correlation (r=0.97**) with yield. Moreover, the results showed that deficient irrigation regime with supplying 80% of the water requirement reduced the grain yield and water usage by 9 and 12%, respectively and it improved the water productivity by 4.6% compared with the optimum water conditions. Whereas, reducing the amount of irrigation water to 60% of the required water, decreased the water productivity by 13.6% compared with the optimum water conditions. Results showed that the deficit irrigation decreases the yield and yield components. Reducing water usage to 80% of water requirement reduced the water usage to 12%, consequently, although the water productivity increased, the yield decreased by 9%. Thus, it could be a suitable approach for regions with low water reservoirs. In the other words, in low water regions, the best choice to manage optimum irrigation to achieve constant production and increasing usable water is “the lower water-the higher productivity” strategy. Increasing wild oat density up to 20 plants m-2 had no significant effect on the grain and biological yield of wheat. However, increasing wild oat density up to 80 plants m2 decreased these properties under all irrigation regimes. The insensitivity of wheat to wild oat competition in lower densities is due to the growth characteristics and competitive ability of Alvand variety.