Effect of Plant Density and Weed Interference on Yield and Yied Components of Grain Sorghum

Introduction Weed control is an essential part of all crop production systems. Weeds reduce yields by competing with crops for water, nutrients, and sunlight. Weeds also directly reduce profits by hindering harvest operations, lowering crop quality, and producing chemicals which are harmful to crop plants. Plant density is an efficient management tool for maximizing grain yield by increasing the capture of solar radiation within the canopy, which can significantly affect development of crop-weed association. The response of yield and yield components to weed competition varies by crop and weeds species and weeds interference duration. The objective of the present study was to evaluate the effect of weed interference periods and plant density on the yield and yield components of sorghum. Materials and Methods In order to study the effect of plant density and weeds interference on weeds traits, yield and yield components of sorghum (Var. Saravan), an experiment was conducted as in factorial based on a randomized complete block design with three replications at the research field of Islamic Azad University, Birjand Branch in South Khorasan province during year of 2013. Experimental treatments consisted of three plant density (10, 20 and 30 plants m-2)) and four weeds interference (weed free until end of growth season, interference until 6-8 leaf stage, interference until stage of panicle emergence, interference until end of growth season). Measuring traits included the panicle length, number of panicle per plant, number of panicle per m2, number of seed per panicle, 1000-seed weight, seed yield, biological yield, number and weight of weeds per m2. Weed sampling in each plot have done manually from a square meter and different weed species counted and oven dried at 72 °C for 48 hours. MSTAT-C statistical software used for data analysis and means compared with Duncan multiple range test at 5% probability level. Results and Discussion Results showed that all measured traits except seed yield were significantly affected by plant density. Although the increase in plant density from 10 to 30 plants m-2 significantly decreased panicle number per plant, number of seed per panicle and 1000-seed weight by 45.5, 16.2 and 12.3%, respectively but significantly increased number of panicle per m2 by 54.3%. This subject caused seed yield did not show significant changes as plant density per area unit was changed. Also, means comparison showed that increase in density from 10 to 30 plants m-2 had positive significant effect on biological yield so that its increased by 56.7%. Interference treatment had significant effect on all measured traits except number of panicle per plant. Traits of 1000-seed weight, seed yield and biological yield decreased considerably by extending of weeds interference period and the highest seed yield with 350.04.37 g. m-2 achieved in treatment of weed free until end of growth season which were 18.9, 47.6 and 73 percent more than interference until 6-8 leaf stage, interference until stage of panicle emergence, interference until end of growth season, respectively. Also, weed interference until the end of growing season of sorghum reduced biological yield by 59.9 percent compared to treatment of weed free until end of growth season. The highest weed density with 182 plants per m2 was observed in interference until 6-8 leaf stage and weed density per unit area reduced by increase in interference period. Despite the declining in weed density, weeds dry weight per m2 was increased by increasing interference period until the end of growth season. On other word, weeds were in early development, with high density and low dry mass accumulation, which are desirable from a technical point of view for weed control. Conclusions This research showed that increase in plant density non significantly increased on seed yield but change of density from 10 to 30 plants m-2 had positive significant effect on biological yield. Moreover, presence of weeds in farm of grain sorghum is inhibitor factor for maximum production. Weed interference decreased seed and biological yields of sorghum by decline in yield components and tillering. Given that Saravan variety is a plant of double purpose (grain and forage) can be suggested density of 10 plants per m2 and weed free until the end of growth season treatment for sorghum (Var. Saravan) cultivation in Birjand region. Also, evaluation of higher densities of sorghum (Var. Saravan) and early season interference can be recommended for subsequent studies.