April 5, 2011
Some Brazilian Farmers Planting Back-to-back Soybean Crops
After soybean rust was discovered in Brazil during the 2000/01 growing season, it was assumed that the disease would put an end the practice of growing two or maybe even three crops of soybeans a year in the same field. For a number of years it did preclude planting back-to-back crops of soybeans in the same field, but with higher prices for soybeans and better methods of controlling soybeans rust, the practice of growing two crops of soybeans in the same field is making a small comeback
The 90-day soybean free period, which was instituted five years ago as a way to combat soybean rust, precludes anyone from planting three crops of soybeans per year, but it hasn't stopped a few farmers from experimenting with two crops of soybeans per year. As much as a hundred thousand hectares of safrinha soybeans are already being planted in Mato Grosso as well as in Parana and Sao Paulo. The total amount is not known because the state or federal governments have not tracked this new phenomenon.
In Mato Grosso, the 90-day soybean free period begins on June 15th, so in order to get two crops of soybeans per year, both crops must be early maturing soybeans and the first crop must be planted before the end of October. As soon as the first crop is harvested in January or early February, the second crop is no-till planted immediately.
The biggest problem with back-to-back soybean crops is trying to control soybean rust as well as other soybean diseases and pests. The process of harvesting soybeans tends to release huge amounts of rust spores that can spread to nearby fields of soybeans that are still green and in vegetative development. As a result, these safrinha soybeans will need to be treated with fungicides at least three or four times during their lifecycle in order to keep the disease under control.
Needless to say, scientists in Brazil are unanimously opposed the practice of back-to-back soybean crops. They point out that if soybeans are grown continuously for nine months of the year, there is never a chance to break the disease or pest cycles. They feel that such a practice will quickly lead to more disease pressure from soybean rust and other foliar diseases. The populations of insects that feed on soybean leaves and nematodes that feed on soybean roots would also quickly increase with this practice. The temporary monetary gain of a few producers could lead to long term negative impacts on the rest of the soybean producers.
They are particularly upset because a good alternative already exists, and that is a second crop of corn following soybeans. Planting a second crop of corn breaks the disease and pest cycles and corn can also take advantage of the nitrogen that soybean plants remove from the atmosphere and leave in the soil once the crop is harvested. The nitrogen would be completely lost if a second crop of soybeans are planted.
The planting of back-to-back crops of Roundup Ready soybeans could also increase the amount of Roundup Resistant weeds that are already become a problem in Brazil. Roundup resistant foxtail and a native grass called capim amargoso are already major concerns for soybean farmers and planting back-to-back soybean crops would just make the problem even worse.