Evaluation of sorghum residues in combination with reduced herbicide dosage on weed control and barley yield

Introduction
The potential yield reduction caused by uncontrolled growth of weeds during the growing season depends on plant species, weed species, weed density. Weeds and ecological factors are estimated from 45 to 95%. The use of herbicides has been one of the main solutions for the development of agriculture in the past decades. However, the continuous use of synthetic herbicides has increased the number of herbicide-resistant weed biotypes and is considered a serious threat to the environment and public health. One of the methods of weed control that has a great prospect for increasing the yield of crops on one hand and maintaining the integrity of the environmental conditions on the other hand, is re-injury. Among all the possible strategies, modified plant residues are the most successful, effective and easiest method. In a report, sorghum extract reduced the dry weight of weeds by 22-46%. In the same order, the application of modified plant residues in combination with reduced amounts of herbicides in suppressing weeds in crops had results similar to the recommended amount. Since, the information related to the potential of using a combination of sorghum residues in combination with a reduced amount of metsulfuron + sulfosulfuron herbicides to control weeds in barley cultivation is not available. In this regard, this research was carried out with the aim of controlling weeds and improving crop yield.
Materials & Methods
The main experiment was conducted on November 20, 2019 based on randomized complete blocks with four replications. The treatments, including sorghum residues in three concentrations of three, five and seven tons per hectare with or without 50% of the recommended amount of metsulfuron + sulfosulfuron herbicide (20 grams per hectare), control control, 50 and 100 percent (40 grams per hectare) the recommended amount of Metsulfuron + Sulfosulfuron herbicide in plots measuring 4 x 3 m2 and including 10 crop lines. They were performed at intervals of 25 cm. Spraying operation, 50 days after planting, using a back-mounted motorized sprayer, MATABI model, single nozzle, T-jet with number VS_8002 and spraying width of one meter and after calibrating was done. Investigated traits include: the density and dry weight of weeds per unit area were determined in each plot, 130 days after planting. Statistical analysis by SAS software, , the averages were checked using the Least Significant Difference (LSD) test at the 5% probability level.
Results & Discussion
The effects of experimental treatments including the amount of residues and the simultaneous application of residues and the reduced amount of herbicide on density and dry matter of weeds were significant .By increasing the mixing rate of sorghum residues from three to seven tons per hectare, the percentage of weed density reduction increased significantly from 23.9% in the treatment of three tons to 49.4% in the treatment of seven tons. The dry matter of weeds also decreased significantly from 31.2 to 48.5 percent by increasing the mixing rate of sorghum residues from three to seven tons. When the treatment of the reduced amount of herbicide was applied in the plots containing sorghum residues, the effectiveness and inhibition of weed growth was in most cases equal to or even higher than the recommended amount of herbicide. This event indicates the existence of a complementary interaction between herbicides and harmful compounds. The highest yield with 1.5 t.ha-1 was observed in the combined treatment of three tons of residues, which was not significantly different from the treatment with the recommended amount of herbicide with a yield of 4.9 5 t.ha-1. The improvement of barley yield and the number of spikes in the integrated treatments of herbicide and sorghum residues in amounts of three and five 5 t.ha-1 compared to the control treatment is the result of the reduction of crop-weed competition for each of the growth factors. Suppression of weed growth leads to increased yield.
Conclusions
The present study showed that it is possible to use the natural potential of sorghum residues in combination with the reduced amount of metsulfuron + sulfosulfuron and reduce the consumption of this herbicide by 50%. Increasing the mixing of more than 3 tons of sorghum residues with the soil, despite more appropriate control of weeds in combined treatments, resulted in a decrease in yield.