Ibrahim S. Alsaadawi and Ali K. Sarbout
Department of Biology, College of Science, Baghdad University, Baghdad, Iraq
A field trial was conducted with the aim of utilizing sunflower residues to reduce the input of herbicide in cowpea field. Sunflower residues at rates of 3 and 6 t ha-1 were incorporated alone or in combination with reduced (50% of the label rate) rate of trifuralin herbicide. Weedy check, weed free and label rate (2.4 L ha-1) of herbicide were also included for comparison. Results indicated that Incorporation of sunflower residues in to field soil at 3 and 6 t ha-1 significantly reduced weed population by 54 and 75% of control and weed dry weight biomass by 72 and 82% over control, respectively. However, combination of lower rate of trifluralin and sunflower residues at 6 t ha-1 significantly reduced weed density and weed population by 79 and 90% over control, respectively while combination of lower rate of herbicide and residue rate at 3 t ha-1 provide 68% higher weed biomass suppression over the control. Maximum seed yield (5.1 t ha-1) and biological yield (19.64 t ha-1) of cowpea was recorded by integration of reduced rate of herbicide with sunflower residues rate at 6 t ha-1 which was greater than the label rate of herbicide. Chemical analysis on field soil amended with sunflower residues revealed the presence of phenolic compounds in soil which were started to release after two weeks of decomposition, reached its peak at 4-week and remained at higher concentration until 8-week then declined until reaching the lowest concentration at 10-week of decomposition. Bioassay of soil amended with sunflower residues at different periods of decomposition exhibited a significant suppression of seedling emergence of the test weeds and the higher suppression was highly correlated with the higher quantity of phenolics content of soil. The importance of this approach in reducing the reliance on synthetic herbicide is briefly discussed.
Keywords: Allelopathy, sunflower residues, reduced herbicide, weed management, cowpea
RECEIVED: July 6, 2015
ACCEPTED August 15, 2015