Soybean fact file
- 111 million hectares grown worldwide in 2013
- 90% or more of all soybean fields in USA and Argentina are GM
- 70% increase in productivity since 2000
- 40% of bean weight is oil rich in monounsaturated oleic acid
- 12% of US soybeans were used to make biodiesel in 2014
- 13 million hectares under no-till in USA
Soybeans stand out from other major crops: broad leaved rather than a grass; a legume, so plants supply their own needs for nitrogen fertilizer while increasing the fertility of the land; and soybeans are rich in oil, protein and carbohydrate.
In the US, soybeans are grown on half of the 30 million hectares on which no-till farming is practiced. In Brazil, no-till has also been widely adopted for soybeans. Broad-spectrum herbicides, led by the introduction of paraquat in the 1960s, allowed the adoption and growth of no-till which does not rely on controlling weeds by burial from ploughing.
No-till systems save cash, time and fuel, improve soil structure, reduce erosion and provide havens for wildlife. Paraquat is deactivated on contact with the soil meaning that it can be sprayed to burndown weeds before planting without risking crop damage from root uptake. Paraquat works well even in cold and rainy weather. In double cropping systems (in which two crops are grown in one year) a fast turn-around between crops is critical. Paraquat’s rapid action gives the fastest possible clean-up of weeds before planting the next crop. No-till techniques and using paraquat for weed control can provide this, as well as conserving soil moisture, often giving as much as a 10-day lead over any recommended glyphosate program.
In the US, intensive use of glyphosate, particularly since the introduction of GM glyphosate-resistant varieties, has led to the development of resistant weeds in soybeans and other crops. Resistant horseweed (Conyza canadensis) has become a problem across tens of thousands of hectares in many eastern and southern states since 2000. More recently, other glyphosate-resistant weeds including common ragweed (Ambrosia artemisiifolia) and palmer amaranth (Amaranthus palmeri) have been problems too. No more than two applications of glyphosate should be applied to any one field over two seasons, so paraquat has a valuable role to play as an alternative non-selective herbicide.
When soybeans are grown in wide rows, paraquat is the only non-selective herbicide which can be sprayed to control weeds without fear of crop damage. Equipment with spray nozzles which are shielded to prevent spray drifting off-target is usually used. However, paraquat can be sprayed with unshielded sprayers when the crop is taller than 20 cm and care is taken to avoid spray drifting on to no more than the lower 7 cm of the soybean plants. This practice is not recommended for glyphosate, being far too risky because of its systemic action.