The effect of depth of planting of soybeans and leaching of herbicides by irrigation to weed control and soybean injury

Weeds have presented one of the greatest hazards to good soybean yields. The control of weeds or the lack of it, is one of the most expensive items in the production of soybeans on American farms. Weeds compete with soybeans for water, light and nutrients. They increase the cost of labor, and equipment, reduce the quantity and quality of beans, harbor insects and diseases and reduce the efficiency of mechanical production and harvest. Weed research in the past has conservatively estimated the loss due to weeds to about 17 percent of the annual value of the soybean crop or approximately 136 million dollars each year (10, 29). The science of weed control has advanced considerably during the past two decades. A number of herbicides are now available for weed control in soybeans. However, none of them will control all of the weeds without the risk of injury to the bean crop. According to environmental conditions, they have also showed either a variable response in weed control activity or injury to the beans. This is primarily due to the fact, that soybeans do not possess sufficient tolerance to the herbicides at currently recommended rates under soil moisture and temperature variations that exist. Burnside and Lipke observed reduced weed control when applications of water were delayed as little as four days following pre-emergence application of 3-amino-2,5- dichlorobenzoic acid (amiben), (7). The importance of rain in the use of pre-emergence herbicides is undisputed, but its importance varies with each herbicide due to differences in such factors as water solubility and ionic charge of the herbicide. The objective of this study was to determine the relationship between depth of planting of soybeans and leaching on the effectiveness of the herbicides.