“The secret to achieving higher corn yields is figuring out why you’re not achieving high corn yields now.” That’s how Bob Nielsen begins his pitch for identifying what might be limiting yields. Nielsen is the Purdue University Extension corn specialist.
“The goal is to identify and figure out how to mitigate yield-limiting factors specific to individual fields,” Nielsen says. “If you fail to identify yield-limiting factors, some agronomic decisions will miss the mark — and either waste money on inputs, leave yield on the table, or both.
“Identifying yield-limiting factors is important because we shouldn’t be spending money on solutions for problems we don’t have!”
Identifying what’s limiting yield requires walking fields and taking notes throughout the season, plus using aerial images and yield maps where appropriate, Nielsen says.
Here are seven yield-limiting factors to examine. There could be others, Nielsen says.
1. Poor soil drainage. Improved soil drainage can reduce ponding and saturated soils. When soils are saturated, chances for nitrogen loss through denitrification increase. Working days are fewer, and planting delays are more likely. Soil compaction from planter and tillage trips is more likely. Cloddy soils, which can interfere with planting, are possible in tillage systems on wet soils. “Improving soil drainage leads to better stand establishment and root development,” Nielsen says.
2. Hybrid performance. “This can be a huge factor. Don’t underestimate it,” Nielsen says. Hybrid selection to match the field can easily result in 20 to 30 more bushels per acre in some cases, he notes. Pay attention to traits related to stress tolerance. Mitigating stress is essential to higher yields. Look for hybrids that consistently yield well across a wide range of growing conditions.
3. Repeated passes with heavy equipment. These trips can cause soil compaction and go hand in hand with poor soil drainage, Nielsen says. “Soil compaction makes poor drainage even poorer and keeps saturated soils saturated longer,” he notes. “Because soil compaction limits rooting depth, it makes corn more susceptible to stress. We saw that in 2019, when some fields seemed to stress faster than they should have when it dried up.”
4. Herbicide-resistant weeds. Tough weeds such as waterhemp or Palmer amaranth can impact corn yields. Bill Johnson, Purdue weed control specialist, notes that waterhemp can hide under a corn canopy if you don’t know it’s in the field. Getting it under control takes time and money.
5. Foliar diseases. Scout to know disease pressures, Nielsen says. Tar spot shows up more frequently in northern Indiana, with southern rust becoming a more common threat in southern Indiana. Gray leaf spot and northern corn leaf blight are always a threat.
6. Nutrient deficiencies and low pH. These may be spatially variable even within a field. One area of a field may be deficient on nutrients while another is not. The same applies for pH. Nielsen suggests regular soil sampling on a small enough scale to find these deficiencies. Address them with variable-rate applications.
7. Secondary or micronutrient deficiencies. Sulfur is the one micronutrient deficiency showing up most often. “We don’t see a response to sulfur in about half our trials, but when we do, it’s often big,” Nielsen says. You can’t monitor sulfur deficiency effectively with soil tests. Consider large-scale field trials to see if sulfur helps, he concludes.