The Surprising 2013 Soybean Crop

The 2013 growing season in Illinois was wet early with delayed crop planting, good rainfall in June and July, mostly cool conditions in July, and little rainfall in August and September, with some high temperatures in late August and in September. With late planting and cool weather at times in mid-summer, seedfillling began only in mid-August, 10 days to 2 weeks later than normal, and took place during a period of very little rainfall. Our expectation for such a season, especially after the dry early-wet late season that revived the crop in 2012, is for a season like 2013 to be a mediocre or even poor one for soybean yields.

But Illinois soybean yields in 2013 surprised nearly everyone: harvest was delayed, seeds filled well, and the average yield for Illinois, according to the November 1 estimate, is expected to be 49 bushels per acre. This compares to 43 bushels per acre in 2012, and if it holds up it will be the third-highest on record, below 50.5 bushels in 2004 and 51.5 bushels in 2011.

Planting date:

Statewide, soybeans were planted late or very late in 2013, reaching 50% planted only about June 1. Results from our trials showed that yield loss from late planting in 2013 was less than we have found in recent years; planting in late May or early June this year produced nearly the same yields as planting in late April or early May. In previous work we have found more advantage to early planting when yield levels are high. We did not see this in 2013; in fact, at the highest-yielding site there was almost no planting date response.

Results in 2013 don’t change the fact that planting early when conditions permit is sound management. But we did learn that a good start to the season can help overcome late-season stress, and that having the crop in good shape at the start of seedfilling might be more important than simply planting early. With such low late-season rainfall, it’s likely that the temperatures in 2013 extended the flowering process and pushed seedfilling into a more favorable part of the season, regardless of when the crop was planted.

Row spacing:

Averaged across sites, soybeans in 15-inch rows outyielded those in 30-inch rows by nearly 4 bushels per acre in 2013. This is about double the response we saw over the previous three years. With reasonably good (though delayed) canopy development in the 2013 crop, we expected that narrow rows might be more valuable for late-planted soybeans. Some of the larger responses did come at later plantings, but this was not consistent among sites. So while we think that it helps that early-planted soybeans develop their canopy earlier, it’s clear that when the canopy “closes” on soybean is not the only thing that matters in setting yield potential.

Fungicide and insecticide:

We found less yield response to foliar fungicide-insecticide applications in 2013 than we have seen in most recent years; the average yield increase was less than 1 bushel, and the response was statistically significant at only one of six sites of our sites. With few diseases or insects to control, we often do not have a good explanation for why such yield increases are sometimes seen, though some have claimed that fungicides can increase yields by reducing stress effects. In 2013, either such stress did not occur while fungicides were still present in the plant or this effect simply didn’t kick in.

Combinations of inputs:

In recent years we’ve been conducting a series of “high-yield” trials in which we use 15-inch rows and combinations of inputs – micronutrients, nitrogen fertilizer, fungicide/insecticide, growth regulators, and lactofen (Cobra®) herbicide – combinations that have been promoted as a key to increasing soybean yields. Among three locations in 2013, yields ranged from nearly 90 bushels per acre to less than half that. At the low-yielding site (Brownstown), adding some of these inputs increased yields by 3 to 4 bushels per acre. But at the highest-yielding site (Urbana), the only effect we found was from use of Cobra®, which reduced yield by nearly 10 bushels per acre. These results are not inconsistent with those from previous years and other locations. It is clear by now that using herbicides like lactofen is more likely to reduce soybean yields than to increase them.

Nitrogen:

Use of nitrogen fertilizer continues to be promoted for soybeans, with the reasoning being that a crop that produces very high yields won’t be able to provide the resources needed to fix enough N for full crop yield. In 2013, as in previous years, we were unable to increase soybean yields by application of fertilizer N during the season. Yields in these trials have ranged from less than 40 to about 90 bushels per acre, and N fertilizer has produced no response regardless of yield level. We haven’t given up on looking for ways that N fertilizer might be used to increase yields, but we think that this might involve a new approach, perhaps looking for signals from the crop that indicate a need for N before it is applied.

Irrigation:

In the past two years we have run a trial at Urbana in which we irrigate soybeans, along with adding in-season N fertilizer and fungicide+insecticide. Under the very dry conditions of 2012, irrigating soybeans, mostly in July and August, increased yield from 70 to 83 bushels per acre. In 2013, it was drier late in the season than in 2012, and application of a total of 7 inches of water in August and September this year increased yield by 9 bushels, from 64 to 73 bushels per acre. Fungicide/insecticide increased yield by about 4 bushels per acre with or without irrigation in 2013, but fertilizer N produced no response regardless of irrigation.

Lessons:

We often like to think (and say) that research results from “odd” years don’t teach us much, since we don’t expect such years very often, so can’t manage based on these results. I disagree – every season and every site tells us something about the crop and how it responds to what we do. If nothing else, we get an idea from such studies about how often, not just how much, inputs will provide a response. We often can only speculate about reasons for things turning out differently than we expected, but that’s part of the learning process.

The Illinois Soybean Association supported much of this research, for which I’m grateful. I’ll be addressing the topic of getting high soybeans yields at the 2014 Corn and Soybean Classics, and hope to see everyone there.