ABSTRACT
The soybean is the most important grain legume crop in the world in terms of its use in human foods and livestock feeds. Soybean is unique in having high concentrations of both oil and protein. It has the highest protein concentration of all edible legumes (Breene et al., 1988; Kumudini et al., 2005). Approximately one-third of the world’s edible oils and two-thirds of the world’s protein meal are derived from soybean (Golbitz, 2004; Temperly and Borges, 2006). The soybean belongs to the family Leguminosae, subfamily Papilionoideae, and the genus Glycine L. The cultivated species is Glycine max (L.) Merrill. Soybean apparently originated in China and was introduced into Europe in the early 1700s and into North America in the early 1800s (Whigham, 1983). Important soybean-producing countries are the United States, Brazil, China, and Argentina. The eight major soybean-producing countries in 2007 were the United States (72.9 million metric tons, Mt), Brazil (57.9 Mt), Argentina (47.5 Mt), China (13.8 Mt), India (11.0 Mt), Paraguay (5.86 Mt), Canada (2.70 Mt), and Bolivia (1.60 Mt). Since 1970, soybean production has been at least double that of any other oilseed crop. The improvement in soybean production is associated with both improvements in genetics as well as management practices. Two management practices that have revolutionized soybean production in most of the soybean-producing countries are reduced row spacing or increasing plant populations and release of glyphosate (herbicide)-resistant cultivars. Bertram and Pedersen (2004) reported that, averaged across weed management systems and plant populations, 19 and 38 cm rows yielded 7%, 9%, and 10% more than 76 cm rows in southern, central, and northern Wisconsin, respectively. Soybean planted in narrow rows (<76 cm) intercept more sunlight than wide rows (Bertram and Pedersen, 2004) and suffer less weed competition (Forcella et al., 1992). Similarly, glyphosate-resistant soybean was one of the ˜rst major successes of genetic engineering (Padgette et al., 1996). King et al. (2001) reported advances in biotechnology resulting in glyphosate-tolerant soybean cultivars, providing an effective broadspectrum postemergence weed control option. Glyphosate applied at labeled rates does not affect glyphosate-resistant soybean adversely (Nelson and Renner, 1999).
