N-fixing legume, soil improver
Soybean is an N-fixing legume. It can be used as green manure or as a rotation crop in combination with cotton, maize and sorghum. During the first 6-8 weeks after seedling, soya has to be weeded. After that period, its rapid growth can reduce weeds. In Africa, it is reported to reduce the parasitic weed Striga hermonthica which is very noxious to crops (Giller et al., 2007).
Loss of biodiversity
The intensive monoculture of soybean in Brazil and Argentina has a negative effect on habitats and biodiversity. Soil erosion increases with mechanical weeding, and intensive cultivation results in a severe mining of soil fertility. Soybean cultivation is also responsible for massive deforestation in Brazil, Argentina and Paraguay (Steinfeld et al., 2006).
Genetically modified soybeans
The debate about the environmental impact of GM crops is complex and a full discussion of the issue is beyond the scope of this datasheet. The actual reduction in herbicide use due to the introduction of glyphosate-resistant soybeans is disputed. The decrease of 10% found by certain authors can be considered too modest (or linked to factors other than GM soybean), or significant enough because of the large areas cultivated with soybeans. Other authors consider that herbicide-tolerant soybeans can have indirect environmental benefits by encouraging farmers to use no-tillage or conservation tillage practices that reduce soil erosion and fuel use (Edwards et al., 2009). Spontaneous, pollen-mediated gene flow has been observed but is considered too limited to be an issue. However, gene flow by seed is highly probable. Transgen introgression into wild soybeans in China and Korea, while possible, is also considered too limited to be of real concern (Owen, 2009).