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February 24, 2012

Indeterminate Soybeans Replacing Determinate Varieties in Brazil

One of the biggest changes in Brazilian soybean production in the last few years has been the rapid adoption of indeterminate soybean varieties. Just a few years ago nearly all the soybeans grown in Brazil were determinate varieties and now it is estimated that over half of Brazilian soybeans are indeterminate and it is expected to eventually reach 100%.

An indeterminate soybean plant continues to grow and put on new leaves and nodes at the top of the plant while at the same time, the plant sets flowers and pods at the bottom of the plant. As the growing season progresses, there may be full size pods at the bottom of the plant while at the top of the plant new leaves are still emerging. Determinate soybeans have a different growth pattern. Determinate soybeans complete their growth cycle first before they start to flower and set pods. So a determinate soybean may be 3-4 feet tall and not have any flowers or pods whereas a determinate soybean may already be setting pods when the plant is 1-2 feet tall.

The huge advantage of indeterminate soybeans over determinate varieties is the fact that they can recuperate after periods of dry weather. If there is a period of hot and dry weather when the indeterminate varieties are setting flowers and pods at the lower nodes, the plant may abort those flowers and pods, but if improved rainfall occurs later in the growing season, the plant can set new flowers and pods at the top of the plant. The plant is probably not going to recoup everything that was lost previously, but some will be recuperated.

The disadvantage with determinate soybeans is that if the period of hot and dry weather hits when the plant is flowering and setting pods, the plant may abort many of the flowers and pods and there is never a chance to set new ones later.

One of the main reasons why indeterminate soybeans have moved so quickly into Brazil is the increasing amount of early maturing soybeans that are being planted. Farmers are planting more early maturing soybeans because they want to have enough time to plant a second crop after the soybeans are harvested. Generally by nature the early maturing varieties are indeterminate and only the latest maturing varieties are determinate, but plant breeders are putting the trait into later maturing varieties. The indeterminate varieties in Brazil mature approximately two weeks earlier than the determinate varieties

An indeterminate soybean has a more stable production than a determinate soybean because it always the ability to at least partially compensate for earlier problems. Good growing conditions near the end of the plant's life cycle can often time result in surprisingly good yields. That is what makes soybean yields so difficult to estimate before the plant is mature. In the U.S., where nearly all the soybeans are indeterminate, accurate soybean estimates cannot be made until about the second half of August when the plants approach maturity.

As an illustration of just how fast this technology is being adopted in Brazil, in a municipality in western Parana 95% of the soybeans are now indeterminate compared to only 5% during the 2002/03 growing season.