Effect of Integrated Weed Management Methods on Yield and Yield Components of Corn (Zea mays L.) in Kermanshah Province, Iran

Corn (Zea mays L.) is cultivated widely throughout the world and has the highest production among the cerealsafter rice and wheat. In Iran the total production of corn in 2013 was more than 2540000 tons. Weeds are one of the greatest limiting factors to decrease corn yield in Iran as the average yield loss due to weeds in the fields of Kermanshah in 2009 was 17.32 %. The herbicides are the main weed control method in conventional cropping systems but their application has been increased herbicide resistant weeds and environmental pollution. Integrated weed management combines all applicable including chemical and non-chemical methods to reduce the effect of weeds in the cropping systems. Thus, Weed control strategies such as tillage, mulch, cover crops and intercropping could be used for integrated weed management of corn. Previous studies showed that crop residues such as rye (Secale sereal L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and clover (Trifolium sp.), cover crops and living mulch could inhibit weed germination and growth. Therefore the objective of this study was evaluating the effects of some integrated weed management treatments on weed characteristics, yield components and grain yield of corn.
In order to evaluate the effect of some weed management treatments on corn (Zea mays L.) yield an experiment was conducted in 2014 in Ravansar, Kermanshah, Iran. This study was arranged based on randomized complete block design with 10 treatments and three replications. The weed management treatments were including 1-chemical control followed by mechanical control (application of nicosulfuron at a dose of 80 g.a.i.ha-1 cultivator 40 days after emergence) 2- chemical control followed by mechanical control (application of 2,4-D〣 at a dose of 675 g.a.i.ha-1 cultivator 40 days after emergence) 3- cultural control followed by mechanical control (planting hairy vetch (Vicia villosa) in the fall 狩涊 40 days after emergence)4- mechanical control (cultivator 25 and 40 days after emergence) 5- cultural control (intercropping of corn with chickpea (Cicer arietinum L.) at density of 200000 plants.ha-1 6- cultural control followed by other cultural control (planting hairy vetch in the fall 詻庭쫨Ꚙ of corn with chickpea) 7- chemical control followed by cultural control (application of glyphosate at a dose of 2050 g.a.i.ha-1 before planting詻庭쫨Ꚙ of corn with chickpea) 8- cultural control (straw mulch application in the fall in amount of 2625 kg.ha-1) 9- cultural control (straw mulch application in the spring in amount of 2625 kg.ha-1) 10- hand weeding during whole season. Also the weed infested treatment was used as control. Sixty days after corn emergence, the weed sampling was done with 1×0.5 (0.5 m2) quadrate in each plot and weed density was recorded. The samples were dried in 75 ºC oven for 48 hours thenweed dry matter was measured. The plant height and leaf number per plant were measured in all plots. Corn was harvested at economic maturity and grain yield and yield components of corn and weed biomass were measured. The analysis of variance of data was performed using SPSS v.16 and Duncan's multiple range procedure was employed at probability level of 5%.
Results indicated that different weed management treatments had significant effect on weed density and dry matter, corn plant height, leaf number per plant, number of kernel rows per ear, number of kernels per row, number of kernels per ear and corn grain yield (p≤ 0.01). The lowest weed dry matter were obtained in 2, 4-D MCPA cultivator treatment (72 g.m-2) and the highest one observed in intercropping with chickpea (440 g.m-2) and mulch application in the fall (441 g.m-2). The highest value of plant height, number of kernel rows per ear, number of kernels per row and number of kernels per ear were observed in 2,4-D MCPA cultivator, nicosulfuron cultivator and hairy vetch cultivator treatments. The highest corn grain yield was obtained in 2, 4-D MCPA cultivator (8.37 ton.ha-1), nicosulfuron cultivator (6.5 ton.ha-1) and hairy vetch cultivator (6.3 ton.ha-1) treatments, respectively. Also, the lowest grain yield was obtained in mulch application in the fall (1.95 ton.ha-1), intercropping with chickpea (1.96 ton.ha-1) and hairy vetch intercropping with chickpea (2.1 ton.ha-1) that were not significantly different with weed infested treatment. Generally we can conclude that application of cultivator with herbicides had the highest efficacy in weed management of corn.
Among the weed management treatments application of 2,4-D MCPA cultivator, nicosulfuron cultivator and hairy vetch cultivator treatments had the most efficiency in corn weed management. This result indicates the importance of cultivator in corn weed management and also it should be used 40 days after corn emergence for high efficacy in weed control. The treatments of intercropping with chickpea and straw mulch had no enough efficacy in corn weed management and should be integrated with other methods. Using non-chemical methods in corn weed management may be causes yield loss but reduces application of herbicides and environmental pollution that is consistent with sustainable agriculture.