Evaluation of competitive parameters of wheat (Triticum aestivum L.) and rye (Secale cereal L.) under drought steers condition by using reciprocal yield model

Introduction Weed is unwanted and harmful plant which annoyed or barrier in agricultural operations and increase the cost of the kept and reducing crop yields. Weeds often compete with crops for limited resources such as soil water and reduced water availability in crops. One of the important principles of integrated weeds management is the development of strategies for weed control based on recognition of the interaction between crop and weeds and quantity competition between crops and weeds is requisite for weed management decisions. One of the valid models for estimating the amount of competition between two species in mixed culture is the reciprocal method of one plant yield. Wheat in terms of production and Cultivated area is the most important of crops in Iran and world. Wheat production in world is about 728.8 million tons in 2015-2016. Weed problem in wheat is one of the most important agricultural issues in wheat growing areas of world and Plant community combination of wheat weeds are a reflection of planting season, agronomic and chemical weed control, geographical region and type of soil. In Iran many areas that under cultivated wheat faced with rye. Low expectations of rye with the ability of allelopathic and Morphology and similar life cycle with wheat, caused increasing of its area in winter wheat fields. Materials and methods In order to study the evaluation of competitive parameters of Wheat and Rye under drought stress condition by using reciprocal yield model, a pot experiment was conducted in the greenhouse of Agriculture College at University of Birjand in 2012. The experiment arranged as factorial based on completely randomized design with three replications. The factors including four wheat density: 0, 8, 16, 24 plants / pot, four rye density: 0, 2, 4, 6 plants / pot and two levels of drought stress: irrigation after depletion of 20 and 60% of field capacity moisture.Models of reciprocal yield were fitted based on biological yield of one wheat plant and rye in two moisture levels and Relation reciprocal biological yield of one wheat plant and rye was obtained with density of two plants by using multivariate linear regression. Also relative competitive ability and Nich differentiation Index calculated by the coefficients of inter and intra specific competition. Results and discussion The result of reciprocal yield model showed that wheat had greater inter-specific competition than intra-specific, but in rye intra-specific was higher. The ability index of relative competition exhibited that effect of a wheat plant in 20 and 60% depletion of soil moisture was equal to effect of 0.79 and 0.64 of a rye plant, respectively. So, effect of a rye plant at the same moisture level was equal to 1.85 and 2.43 of a wheat plant, respectively. Ecological niche differentiation index of both plants was obtained less than 1 in each of two moisture levels. So that the Nich differentiation Index in 20 and 60% of field capacity moisture was about of 1.46 and 1.55 respectively. Conclusion Relative competitive ability or rye and wheat with increasing drought stress increased and decreased, respectively. Biological yield of wheat more affected by inter-specific competition as a result rye compared to wheat was stronger competitor. Combined effects of drought stress and rye competition significantly decreased biological yield of wheat. Generally, under drought stress, intensity of intra and inter specific competition increased between rye and wheat plants and resulted to decreasing of biological yield of those plants. As a result, control of rye in drought stress condition is very important in wheat fields.