Soybean cropping

Soybeans in a podSoybean stands 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; soybeans are rich in oil, protein and carbohydrate; and the crop has been highly developed by plant breeders and agronomists. This makes soybean arguably the world’s most versatile crop. With such a broad nutritional base, soybeans are a staple food and animal feed. Whole beans provide flours; soya oil is used in cooking and food; protein-rich soya meal left after oil extraction is an important livestock feed; and soya protein is used in drinks, baby food, noodles, and as a meat and dairy substitute. A significant amount of soybean production in the US, in particular, now goes to make biodiesel


Mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats for use in diesel engines. It refers to pure fuel before blending with conventional diesel fuel. Blends are denoted as, "BXX" with "XX" representing the percentage of biodiesel contained in the blend (ie: B20 is 20% biodiesel, 80% petroleum diesel).

Authoritative On-line References and Resources The US Department of Energy's Office of Energy Efficiency and Renewable Energy has an Alternative Fuels and Advanced Vehicles Data Center containing key information on all biofuels.
(5 to 10% each year). Biodiesel is not soya’s first connection with motor vehicles. In 1941, Henry Ford’s enthusiasm for finding industrial uses for crops resulted in the manufacture of the ‘Biological Car’ made for an exhibition. The vehicle’s entire bodywork was made from plastic derived from soybeans!

Paraquat is an essential tool for soybean farmers

Paraquat is an important tool in the soybean farmer’s battle against weeds, while also having a good environmental profile and creating opportunities in rural communities. You can read more about the benefits of using paraquat here. Paraquat controls a very broad spectrum of annual weeds


Weeds that complete their life cycle within one growing season, or year. From seed to flowering to seed before the year ends.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world.
, cleaning fields before planting or later tackling weeds growing in between the crop rows.
Paraquat is deactivated on contact with the soil meaning that it can be sprayed to burn down weeds before planting without risking damage to that crop or subsequent crops in the rotation. There are no leaching


The natural process by which water soluble substances are carried downward through the soil into groundwater.
, persistence or root uptake problems to restrict its use, unlike many other herbicides which have ‘residual’ properties.
You can read more about paraquat’s unique soil properties here. Paraquat works well even in cold and rainy weather. These properties mean that it is vital to conservation tillage


Any tillage and planting system that covers 30 percent or more of the soil surface with crop residue after planting to reduce soil erosion by water.

Authoritative On-line References and Resources

Purdue University-based Conservation Technology Information Centre.
systems in which there is no plowing to control weeds. Conservation tillage prevents erosion and maintains a healthy soil. 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.
A video showing paraquat’s unsurpassed speed of action can be viewed here. In recent years, intensive use of glyphosate has caused new weed problems as less well controlled species have ‘shifted’ to become more dominant and some species have evolved biotypes which are resistant to glyphosate. Using paraquat as an alternative non-selective


A chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds).

Authoritative On-line References and Resources An invaluable source of contemporary information about herbicides and weeds from Iowa State University.
herbicide with a different mode of action in integrated weed management


A decision support system for crop protection which focuses on long-term prevention or suppression of pest problems with minimum impact on human health, the environment, and non-target organisms. IPM takes into consideration all available pest control techniques and tactics (cultural, mechanical, biological, chemical). IPM emphasizes the growth of healthy crops for better productivity with the least possible disruption to agroecosystems.

Authoritative On-line References and Resources "The USDA's National Site for the Regional IPM Centers' Information System provides information about US commodities, pests and pest management practices, people and issues."
systems is helping to avoid problems of weed shifts


A change in the weed community within a field i.e. relative abundance or type of weeds. This can be the result of a management practice like herbicide use or any other phenomenon that brings about a change in weed species composition. Species or biotypes adapted to current weed management practices increase, whereas weeds susceptible to those practices decrease.

Authoritative On-line References and Resources A classic article on weed population dynamics on the Iowa State University Weed Science website.
and resistance.
The importance of paraquat in fighting weed resistance to glyphosate and maintaining farmers’ options to use conservation tillage systems is discussed here. Although paraquat is a non-selective, broad spectrum herbicide, if small amounts land on leaves there is little or no crop damage because paraquat does not move through plants systemically like glyphosate. So, paraquat can be used for inter-row weed control to remove weeds growing between the crop rows. This practice is not recommended for glyphosate, being far too risky because of its systemic action. Paraquat has a very robust environmental profile. Details of paraquat’s safety to the environment, spray operators and consumers can be found by referring to the Paraquat Fact Sheet.

What are soybeans?

Soybeans growing in a no-till systemSoybean (Glycine max (L.) Merr.), soya or soy, is a broad-leaved crop. The branching plants grow up to 1 metre in height. As soybeans grow, leaves develop into the characteristic ‘tri-foliate’ arrangement. As a legume, or pulse crop, the roots of soybeans have nodules where bacteria convert nitrogen from the air to forms which are used by plants as nutrients. Soybean varieties have important characteristics which affect where and how they are grown. Determinant varieties will mature ready for harvest when triggered by shortening day length. Indeterminant varieties continue to flower and set seed until the weather becomes unfavorable for growth. The trend of growing soybeans in narrow rows tends to make them grow taller and susceptible to lodging (being flattened by wind and rain). Determinate varieties are shorter and resistant to lodging. After flowering, pods form in clusters of three, each of which usually contains two or three beans. Soybeans are grown principally for the oil (about 20%) and protein (about 40%) in the beans. Soybean oil is rich in oleic acid, a monounsaturated fatty acid, and contains no cholesterol; the protein contains eight amino acids essential to the human diet. Soybeans are also a good source of minerals and vitamins. Lecithin is an important component of the oil used as a solvent, emulsifier, and lubricant; and to make oil-based products such as inks and paints.

Where are soybeans grown?

Figure 1. Global soybean area distribution (FAO 2013 statistics)Soybeans are grown on every continent, from tropical to warmer temperate climates. Temperature and daylength are important factors controlling the development of soybean crops towards harvest and varieties are bred to suit to latitudes and climates. In 2013, more than 111 million hectares of soybeans were harvested around the world – almost 90% more than 20 years ago. Growth has been greatest in South America, with three- to four-fold increases in the areas grown by major producing countries, like Brazil and Argentina. Soybean production is dominated by three countries (Fig 1): USA (31 million ha), Brazil (28 million ha) and Argentina (19 million ha). In the rest of the Americas, Paraguay (3.1 million ha) and Canada (1.8 million ha) are also big producers. In Asia, China (6.6 million ha) and India (12.2 million ha) grow large areas. Over 1 million ha are grown in Africa - South Africa, Nigeria and Uganda growing the largest areas. Europe’s quarter of a million hectares are mainly grown in Italy (134,700 ha) and France (43,000 ha). Best yields generally come from crops on silty loam, moisture retentive, but well drained, soils with neutral to slightly acidic pH. Yields from the best-managed crops in the Americas and Europe are around 3 tonnes/ha while average yields in less-developed countries are only around 1 tonne/ha.

How are soybeans grown?

Soybeans are a ‘row crop’.

In temperate climates soybeans are sown in late spring to summer and harvested in early autumn (eg. April – July sowings and late September – November harvests in the US). Traditionally, seed was planted in wide rows (about 75 cm apart) which enabled weed control by mechanical cultivators while the crop was growing. Selective herbicides


A chemical product used for eliminating certain types of weeds only (ie either grasses or broadleaved weeds) and not affecting specified crops.

Authoritative On-line References and Resources An invaluable source of contemporary information about herbicides and weeds from Iowa State University.
can now control weeds with little or no damage to the crop, so narrower row widths (less than 20 cm) have become popular. These crops are more efficient at capturing sunlight so tend to yield more beans. Soybeans were the first genetically modified (GM) crop, introduced in 1996 in Argentina and the US. Now more than 90% of all soybeans grown in these countries are GM varieties which are not damaged by the broad spectrum herbicide glyphosate. Other major soya producers growing glyphosate-tolerant soya include Canada and Brazil.

Conservation tillage systems

No-till soybeansIn the US, 35% of cropland received no cultivations in 2009, amounting to 36 million hectares (88 million acres) of which around 50% were cropped with soybeans. Corn and cotton covered 30% and 20% of no-till cropland, respectively. In Brazil, there are believed to be over 25 million hectares under no-till and in Argentina, 20 million hectares. Broad-spectrum herbicides, led by the introduction of paraquat in the 1960s, have allowed the adoption and growth of soil cultivation systems which do not rely on controlling weeds by burial from plowing. No-till systems save cash, time and fuel, improves soil structure, reduce erosion and provide havens for wildlife.  

Crop protection

Important insect pests and fungal diseases of soybeans

  • Insects: cutworms (feed on stems); defoliators, eg loopers (feed on leaves); stink bugs (feed on pods).
  • Diseases: damping-off diseases of seedlings eg. Pythium spp., Rhizoctonia spp; Asian Soybean Rust (Phakopsora pachyrhizi).
The susceptibility of soybeans to attack by insect pests and fungal diseases depends on the climate, being more severe in hot humid conditions. In cooler, drier conditions such as the US Midwest and Canada, pests and diseases usually pose little threat to the crop. However, over the past decade, the spread of Asian Soybean Rust (Phakopsora pachyrhizi) up through Latin America into the US has caused alarm. Weeds are a major problem in soybeans whatever the climate. Predominant grass weeds found in most growing regions include barnyardgrass (Echinochloa crus-galli), crabgrasses (Digitaria spp.), signalgrasses (Brachiaria spp) and goosegrass (Eleusine indica). Major broad-leaved weeds include morningglories (Ipomoea spp), pigweeds (Amaranthus spp.), cockleburs (Xanthium spp.), and velvetleaf (Abutilon theophrasti).

The role of herbicides in soybeans

Herbicides can be used before or after crops have been planted:
  • Pre-planting or pre-emergence: to burn down weeds present using contact herbicides such as paraquat or glyphosate, sometimes together with residual herbicides which prevent the germination or emergence of new flushes of weeds. Some residual herbicides require incorporating in to the soil before the crop is planted. Paraquat is safe to use right up until the first signs of emergence.
  • Post-emergence: by use of selective herbicides or inter-row weed control with paraquat


In no-till or conservation tillage systems weeds or a cover crop such as rye, wheat or oats have to be controlled by a burndown herbicide, either paraquat or glyphosate. 2,4-D is often mixed with both of these to improve control of some difficult weeds. A paraquat-diuron mixture is used in Brazil. Paraquat is more reliable than glyphosate in controlling annual weeds and cover crops


Cover crops are primarily planted not to be harvested for food but to reduce soil erosion, control weeds and improve soil quality. They are usually plowed or tilled under before the next food crop is planted, in which cases the "cover crop" is used as a soil amendment and is synonymous with "green manure crop."

Authoritative On-line References and Resources ATTRA is the US National Centre for Appropriate Technology's Sustainable Agriculture Information Centre.
at earlier growth stages when the weather is cold or when rain falls soon after application. Under such challenging weather conditions, paraquat will control weeds in a few days compared to glyphosate’s 2-3 weeks.

Glyphosate resistance and integrated weed management

Horesweed is a troublesome weed resistant to glyphosateIn 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, cotton and corn crops. Resistant horseweed (Conyza canadensis) has become a problem across tens of thousands of hectares of soybeans in many eastern and southern states since 2000. More recently, glyphosate-resistant common ragweed (Ambrosia artemesifolia) has been recorded, too. In Brazil, ryegrass (Lolium multiflorum) resistant to glyphosate has been found. Glyphosate weed resistance also poses a dilemma for soybean no-till farmers in Brazil. As an alternative to glyphosate, paraquat has a valuable role to play in integrated weed management (IWM) systems. No more than two applications of glyphosate should be applied to any one field over two seasons. Paraquat can provide an alternative means of effective and sustainable weed control, as Brazilian soybean growers have discovered. In Brazil, SIC (Sistema Integrado de Controle de plantas daninhas) is one such IWM system. Paraquat is sprayed within a day on either side of soybean emergence as a follow-up to earlier glyphosate application. This minimizes the risk of weeds not controlled by glyphosate becoming a problem and extends the period of weed control such that only one application of post-emergence selective herbicide is needed instead of the normal two.

Inter-row weed control

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 is even safe to spray 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.

Double cropping

Soybeans are often grown in rotation with maize, rice and wheat which benefit from the nitrogen soybeans leave in the soil. In warmer climates, such as the southern US and in Argentina, a soybean crop can be grown after the early harvest of wheat planted the previous autumn. In such double cropping systems the winter crop also protects the soil from erosion. In Brazil, soybeans are grown before a second crop of maize. To double-crop soybeans successfully, a variety must be chosen which will mature more quickly given the later planting as a second crop. Similarly, a fast turn-around time between crops must be achieved and, moving into the summer, conserving soil moisture is also important. No-till techniques and using fast-acting paraquat for weed control can provide this, often giving as much as a 10-day lead over any recommended glyphosate program.

References & Resources

Agronomy and uses

FAO Conservation Agriculture website
USDA report: No-till Farming is a growing practice (2010)
US IPM Centers soybean profiles

Market outlook

USDA Economic Research Service

Glyphosate resistance

International Survey of Herbicide Resistant Weeds