Features Agronomy Soybeans
How early is early for soybeans?

More game plans aimed at boosting soybean yields are including early planting as a standard part of the strategy. Ongoing research in Ontario supports the idea that planting soybeans in early May, if the conditions are fit, can produce a few extra bushels per acre. “We have enough data to recommend early planting,” says Horst Bohner, Ontario Ministry of Agriculture, Food and Rural Affairs soybean specialist. “When you look at what they have done in the US and what has provided extra yield, early planting has come to the table with consistent results.”

Citing five years of data from trials in Ontario, Bohner says planting soybeans in the first week of May produces a yield advantage of about four bushels per acre compared with planting in the last week of the month. That confirms work done in the early 1980s on planting dates. “Sometimes it’s more. Sometimes it’s less. It depends on the year and where you are in the province,” adds Bohner.

Don McClure, soybean breeder with Syngenta Seeds, says the work on early planting quantifies the benefits of allowing the soybean plants to produce more vegetative growth that is conducive to higher yield potential. “When we do have an early planting situation and we’re able to add another node or two to the plant, there is a greater opportunity for more flowers and pods to develop,” explains McClure. “The more vegetative growth we can get before June 21, usually the better off we are as far as yields go.”

McClure says June 21 is a critical date for soybeans because they are “day-length sensitive,” meaning the plant goes into its flowering phase when the days begin to get shorter after June 21. “When they start flowering, they slow down vegetative growth as they shift from one phase of their life cycle to the next,” says McClure.

The warm weather of April 2010 had many farmers across the province asking about early planting during the last two weeks of the month. Whereas Bohner is confident about the research for planting soybeans in early May, he says there is not enough data for April to make a solid recommendation. “If it turns cool, it sometimes takes forever for the beans to get out of the ground, and then you get insects and diseases feeding on the seeds,” says Bohner. He adds that the other main peril of planting too early is the obvious risk of frost damage.

“We are certainly trying to assess the whole issue of early planting. It takes a few years to sort out what you can get away with,” says Bohner of the research on planting in April. “We have a pretty good idea from some of the early work. Going too early can be a detriment in terms of pod set, as well, because the beans can be too short if they get too cold early on, and then you also have the potential problem of thin stands.”

McClure agrees that mid-April is likely pushing the envelope too far for planting soybeans. Whether soybeans are planted early or late, he says the key is to plant when the soil is fit. “The idea is to plant early and into soil that is in very good condition so you can get good stand establishment and get canopy established quickly. That is when you are setting yourself up for a good yield situation,” says McClure.  “But if the conditions are good the last week of April, the soil is in good condition and temperatures are on a warming trend, there is no reason to hold back.”

Other factors to consider
There are more agronomic practices involved with successful early planting than determining the fitness of the soil. Both Bohner and McClure agree that seed treatments can help early planted beans increase their yields. “Part of the reason we’re getting away with these early plantings is that we have better seed treatments, and that does make a difference in terms of stands,” notes Bohner.

Growing a longer-day variety, perhaps 100 to 200 heat units longer than normal for the area, provided it is not going into winter wheat, is another part of the game plan for boosting the yield potential for early planted soybeans. “Last year (2009) we had between five and 10 bushels more by doing that and planting early compared with planting early with the same varieties,” says Bohner. “It’s about capturing as much of the growing season as possible. That means you need to stretch the season on both ends, by planting early in the spring and harvesting later in the fall. A longer-day bean will capture more of the growing season adding more bushels.”

McClure agrees, noting that the success of growing the longer-day beans depends largely on the weather. “We must get consistent rainfall in August because that is the key month for soybeans. If it gets really dry in August, like we had this year (2010), maybe the full-season ones won’t be the best ones, everything else being equal,” says McClure.

In addition to seed treatments and planting longer-day varieties, another practice to keep in mind is planting depth, particularly in the case of no-till soybeans. Bohner says there is a tendency to plant the beans deeper than necessary, especially in early planted fields. “The faster you get the soybeans to come out of the ground, the better. Of course, it will be cooler the earlier you plant, so establishment becomes even more crucial,” says Bohner. “For early planting, keep them on the shallow side. Even if it is on the dry side, I would not put them in below an inch and a half. One inch is usually sufficient unless it’s very dry.”