Agro-ecological evaluation of the effect of sesame plant residue management and chemical control of weeds on wheat yield and weed population in sesame-wheat cultivation pattern in Khuzestan

Introduction
The competition of weeds with crop plants in agricultural ecosystems is one of the most important biological stresses, which causes a high decrease in yield, so their control can have a great effect on increasing crop production. A high population of weeds, especially in the early stages of wheat growth, which have a strong competition for nutrition resources, can reduce the tillering of wheat. The research conducted in the field of plant residue management and chemical control of weeds shows that each of the residue management methods affects the soil and the quantitative and qualitative yield of the next crops. Therefore, considering the direct effect of plant residue management and chemical control of weeds on grain yield of crop plants, especially in double cropping system, this research was conducted to investigate the effect of sesame residue management and chemical control of weeds on weeds population, and wheat yield and yield components.
Materials and methods
To investigate the effect of sesame residues and weed control on wheat yield and weed population, a research was conducted in split-plot based on randomized complete block design with three replications in the research farm of Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran, in the crop year 2019-2019. Residue management at three levels (returning or mixing plant residues with soil, burning residue and removing all residues from the soil) were considered as the main plots and weed control at four levels (chemical control with Metribozin, Atlantis and 2,4-D+MCPA herbicides as post-emergence, and without weeds control as check) as sub-plots, and the studied wheat variety was Mehregan. The traits studied in this research included the number and type of weed species and wheat grain yield and yield components.
Research findings
The results of this research on the number of weeds showed that the highest number of narrow- and broad-leaved weeds was related to the removing plant residues and without weed control treatment. Regarding the wheat yield components, the observations of this experiment showed that the highest number of grains per spike with an average of 49.1 was related to the returning plant residues with the use of Metribuzin (48.7) and Atlantis (49.2) herbicides. The highest wheat grain yield with an average of 4.15 and 4.89 tons/ha was obtained from the treatments of returning plant residues and controlling weeds with Metribuzin herbicide, respectively, and the lowest grain yield (1.85 ton/ha) was recorded for no weed control. The results of this experiment showed that the weeds were effectively controlled by the post emergence application of Atlantis and Metribuzin, respectively.
Conclusion                                                                            
The results of this experiment showed the effectiveness of weed biomass and wheat grain yield in the incorporated sesame residues and weed control treatments. Decrease in the weed population due to the use of chemical herbicides and plant residue management can be attributed to the difference in the biomass of the wheat and weeds in the experimental treatments. Incorporating the plant residues with the soil increased wheat yield components, especially the number of grains per spike, and increased the grain yield and wheat harvest index.