Some Illinois farmers are discovering a frustrating disconnect this harvest: Corn and soybean fields that looked capable of delivering strong yields are producing fewer bushels than expected.
As harvest approaches the halfway mark in north-central Illinois, Ken Ferrie, Farm Journal field agronomist, says corn yields are running 20 to 40 bushels per acre below last year in much of the region. Soybean yields are holding up better, but many fields are still coming in 5 to 10 bushels per acre below 2024 levels.
The gap between promising yield monitor readings and final settlement sheets has become a recurring theme.
“Guys say they’re seeing what they want on the yield monitor going through the field for higher yields, but the settlement sheets are coming up short,” Ferrie says.
The disappointing results aren’t uniform across Illinois. Fields that escaped the worst of June and August rains are generally faring better, underscoring how much this year’s weather and field conditions influenced crop performance.
For farmers evaluating their 2025 results, Ferrie’s observations point to six factors worth examining before making next year’s input decisions.
1. June Rains May Have Changed the Nitrogen Equation.
Of all the factors affecting this year’s corn crop, Ferrie believes nitrogen availability could emerge as the biggest yield driver.
In his ongoing plot work, nitrogen application timing and rate differences appear to be influencing yields more than fungicide treatments or hybrid selection — two factors that typically produce some of the largest yield responses in field trials.
Ferrie suspects the heavy June rains contributed to that shift by causing nitrogen losses.
When soils become saturated, nitrogen in the nitrate form can be lost through leaching or denitrification. Leaching moves nitrate below the crop’s root zone, while denitrification converts nitrate into gases that escape from the soil under oxygen-limited conditions.
The amount of nitrogen lost depends on soil type, drainage, nitrogen form, application timing and the duration of saturated conditions. But when losses occur during a period of rapid corn growth, the crop can struggle to maintain the nitrogen supply needed to support its yield potential.
Ferrie’s preliminary observations suggest that differences in nitrogen rates and timing may have mattered more than usual this season.
If that trend holds through the remainder of harvest, farmers will have an important question to answer this winter: Did their nitrogen program supply enough available nitrogen when the crop needed it most?
That doesn’t automatically mean higher nitrogen rates are the answer. Rather, growers should evaluate application timing, rainfall amounts following application, soil drainage, crop nitrogen demand and the economics of additional fertilizer.
2. Drainage Problem Is Showing Up in Soybean Yield Maps.
Soybeans are generally performing better than corn, but bean yield results are proving less consistent than some farmers anticipated.
While a few fields are approaching last year’s yields, most are running 5 to 10 bushels per acre behind, according to Ferrie.
He expects this year’s soybean yield maps to resemble corn yield maps more closely than usual, with substantial swings within individual fields.
Much of that variability appears related to drainage. Ferrie says growers should study their yield maps to identify whether low-yielding areas correspond with poorly drained sections of a field. Comparing those patterns with previous years’ maps can help distinguish recurring drainage limitations from problems specific to this season.
3. July Heat Left Its Mark on Cornfield Edges.
Ferrie also is receiving reports from farmers of corn yield maps showing sharply defined areas of reduced performance along field edges.
He attributes these patterns to heat-related leaf and plant stress resulting from July’s record heat.
The problem, which Ferrie refers to as “scalded edges,” commonly affects the outside 24 rows, approximately, along the south and west sides of a cornfield next to soybeans or an open area.
Prevailing winds can push hot, dry air across those field boundaries. Increased air movement can raise evapotranspiration — the combined loss of water through soil evaporation and plant transpiration — while lower humidity increases the atmosphere’s demand for water.
“When the crop cannot replace water fast enough, plant temperatures can rise and stress intensifies,” he says.
The result can be reduced photosynthesis and yield potential in the affected rows.
Ferrie notes these patterns sometimes prompt calls from growers who suspect herbicide drift from neighboring fields. But the location and shape of the damage can offer important clues about the actual cause.
4. Planting Date May Help Explain Soybean Seed Discoloration.
Wet weather also has complicated soybean quality assessments this fall.
Ferrie reports numerous cases of discolored soybean seed. In one soybean plot he references, researchers evaluated a single variety with a relative maturity of 3.8 across planting dates ranging from March through June.
“Seed discoloration appeared in every planting-date treatment except those planted in late May and early June,” Ferrie reports.
Ferrie suspects the difference could be related to when the soybeans reached reproductive stages during the summer, potentially placing some planting dates at greater risk during June’s heavy rainfall.
However, plot observations do not yet establish why the discoloration occurred. Seed staining can have multiple causes, and additional evaluation would be needed to determine which factors were responsible.
5. More Nitrogen May Help Explain Why Corn-on-Corn Is Winning.
Another unexpected observation from this year’s harvest is that some growers are reporting higher corn yields in continuous corn than in rotated corn.
Ferrie believes nitrogen management may help explain the difference.
Growers often apply higher nitrogen rates to continuous corn because the crop’s residue can temporarily tie up nitrogen as soil microbes decompose it. Over time, that residue can also contribute nitrogen back to the soil through mineralization, he explains.
Continuous corn also tends to benefit from adequate moisture to help residue decompose and cycle nutrients, although wet conditions can create other challenges, including nitrogen loss.
Ferrie suspects the higher nitrogen rates used in continuous corn may have helped some fields maintain a stronger nitrogen supply this season.
6. High Plant Populations Are Contributing to Down Corn.
Stand population also is emerging as an important factor in fields where corn has lodged or broken over.
As Ferrie harvests population trials, he is seeing how quickly standability can deteriorate as plant populations increase.
In some plots, corn at one population is standing well, while a treatment just 3,000 to 4,000 plants per acre higher looks substantially different, with plants broken over.
“When that corn starts to go down, the yield follows,” Ferrie says.
Lodging can complicate harvest by slowing combine speed, increasing gathering losses and leaving ears or plants difficult to recover. It also can make plot comparisons less reliable when storms or field conditions prevent a clean harvest.
Ferrie says he and his agronomic team at Crop-Tech Consulting, Heyworth, Ill., have lost some plots to severe lodging but has been able to salvage most of its work. Researchers will also need to account for drowned-out areas and other damaged portions of plots when analyzing the results.
Ferrie expects additional insights to emerge as field and plot harvest continues and researchers have more yield data to evaluate.
You can hear Ferrie’s harvest report and recommendations on what to look for as you plan inputs for 2027 in this week’s Boots In the Field podcast, available at the link below:
