The Effects of the Integration of Mechanical Control with Herbicides on Yield and Yield Components of Soybean (Glycine max (L.) Merr.) in Karaj

To study the effects of integration of mechanical control with herbicides on yield and yield components of soybean (Glycine max) a field experiment was conducted during 2003-2004 at the research farm of Agronomy Department, Agriculture Campus of Tehran University, Karaj. A Randomized Complete Block Design (RCBD) of 18 treatments was applied, each treatment being replicated 3 times. Treatments included 5 groups, viz: 1-tifluralin pre planted (960 gr ai/ha), alachlor pre emergence (2400gr ai/ha), bentazon (1200 gr ai/ha) and oxyflourfen (360 gr ai/ha) both post emergence, 2-trifluralin and alachlor plus cultivation or tank mixed with bentazon and/or oxyflourfen, 3-trifluralin and alachlor, plus cultivation and a reduced dose of bentazon (960 gr ai/ha) and/or oxyflourfen (288 gr ai/ha), 4-Trifluralin (1920 gr ai/ha) applied with irrigation water (herbigation) separately, and tank mixed with bentazon or oxyflourfen, and finally 5-weed free check. There were significant differences between treatments regarding weed dry weight at the physiological maturity stage of soybean crop. Trifuralin + oxyfluorfen and alachlor with 95 and 56% control were among the most efficient treatments. Treatments varied significantly with number of lateral branches, 100 seed weight, number of pods/plant, biological yield and harvest index at P=0.01 and number of seeds/pod at P=0.05. The highest (10148 Kg/ha) and the lowest (2981 Kg/ha) biological yields were obtained when applying bentazon at 1200 g ai/ha and alachlor + cultivation + reduced dose of oxyfluorfen at 288 + 2400 g ai/ha, respectively. The highest (2940 Kg/ha) and the lowest yields were obtained when applying trifluralin + bentazon at 1200 + 960 g ai/ha and trifluralin + oxyfluorfen at 360 + 960 g ai/ha, respectively. Best treatments in terms of weed control and optimum yield are considered to be tank mixes of trifluralin and bentazon (1200 + 960 g ai/ha), trifluralin, (plus cultivation), plus a reduced dose of bentazon (960 + 960 g ai/ha).