Field Crops 28.4-58
Mid- and Late-Season Yield Enhancing Management Practices for Corn
Joe Lauer, Corn Agronomist
The 2008 corn production and marketing season is unique. On one hand, it is the
most expensive corn crop ever planted, and on the other, it has the potential to
be the most profitable due to strong market price. If input costs continue to increase,
profit margin will be back to previous years, except with more risk.
So for this year, we have strong prices relative to input costs, thus any production
increase can be more easily paid for. Corn growers have been asking whether there
are any mid- and late-season yield enhancing management practices that can be applied.
Recommended practices versus Trends
To begin this discussion we have to be careful about practices that can be recommended
versus practices that intuitively may trend to greater yields, but are not statistically
significant and thus cannot be recommended. These trends produce responses too small
to be statistically significant.
In agronomic research it is very difficult to detect treatment differences less
than 5%. So in a 200 bu/A yield environment, that means at least 10 bu/A is required
before statistical differences can be detected. What about trends less than 10 bu/A?
At todayï¿½s prices a difference of even 5 bu/A can pay for many inputs. Is there
any guarantee that a trend will make a difference on your farm?
In the 1980ï¿½s, European farmers spurred on by government subsidies attempted to
maximize grain yield. Numerous pre- and planting-season practices were recommended
such as hybrid/variety selection, seed treatments, crop rotation, soil testing and
fertilizer application, N stabilizers, tillage, and pest control. Mid- and late-season
production practices included:
- Split-applications of N
- Foliar fungicides
- Plant growth regulators
- Chelated micronutrients
- Early harvest to prevent ear droppage
Each management practice decision interacts with other practices, but the overall
goal was to maximize yield due to the economic climate. Even small yield changes
could be paid for through government subsidies. Eventually subsidies were removed
and ï¿½Maximum Economic Yieldï¿½ concepts were developed.
Major management objectives for enhancing corn yield
Corn grain yield consists of the components:
- Ear density,
- Kernel number per ear (row number x kernels per row), and
- Kernel weight.
These yield components are determined at different times during the life cycle of
a corn plant. Once corn is midway in development (R1 ï¿½ Silking) the potential number
of ears and kernels is determined. At this stage the major management objectives
- Promote kernel set and grain filling by preventing stress during pollination and
embryo cell division (VT-R2)
- Protect leaves, the photosynthetic factory for kernel filling (ear leaf and upper
Water stress around flowering and pollination delays silking, reduces silk elongation,
and inhibits embryo development after pollination. Moisture stress during this time
reduces corn grain yield 3-8% for each day of stress (Table 1). Moisture or heat
stress interferes with synchronization between pollen shed and silk emergence. Drought
stress may delay silk emergence until pollen shed is nearly or completely finished.
During periods of high temperatures, low relative humidity, and inadequate soil
moisture level, exposed silks may desiccate and become non-receptive to pollen germination.
Table 1. Estimated corn evapotranspiration and yield loss per stress day during various
stages of growth.
Percent yield loss per day of stress
inches per day
16 leaf to tasseling
2.5 - 3.2 - 4.0
3.0 - 6.8 - 8.0
3.0 - 4.2 - 6.0
3.0 - 4.2 - 5.8
3.0 - 4.0 - 5.0
2.5 - 3.0 - 4.0
derived from Rhoads and Bennett (1990) and Shaw (1988)
Water stress during grain-filling increases leaf dying, shortens the grain-filling
period, increases lodging and lowers kernel weight. Water stress during grain-filling
reduces yield 2.5 to 5.8% with each day of stress (Table 4). Kernels are most susceptible
to abortion during the first 2 weeks following pollination, particularly kernels
near the tip of the ear. Tip kernels are generally last to be fertilized, less vigorous
than the rest, and are most susceptible to abortion. Once kernels have reached the
dough stage of development, further yield losses will occur mainly from reductions
in kernel dry weight accumulation.
Severe drought stress that continues into the early stages of kernel development
(blister and milk stages) can easily abort developing kernels. Severe stress during
dough and dent stages of grain fill decreases grain yield primarily due to decreased
kernel weights and is often caused by premature black layer formation in the kernels.
Once grain has reached physiological maturity, stress will have no further physiological
effect on final yield (Table 1).
Premature death of leaves results in yield losses because the photosynthetic 'factory'
output is greatly reduced. The plant may remobilize stored carbohydrates from the
leaves or stalk tissue to the developing ears, but yield potential will still be
lost. Death of all plant tissue prevents any further remobilization of stored carbohydrates
to the developing ear. Whole plant death that occurs before normal black layer formation
will cause premature black layer development, resulting in incomplete grain fill
and lightweight, chaffy grain. Grain moisture will be greater than 35%, requiring
substantial field drydown before harvest.
Split-applications of N
The seasonal pattern of nutrient uptake in corn is similar to that of dry matter
accumulation. A nutrient supplied to the plant when rapidly growing is the most
effective way to utilize nutrients. By VT, about 65% of the nitrogen has been taken
up by the plant, so N application at this time can be of benefit and contribute
to yield. Nitrogen is translocated from vegetative plant parts to the developing
grain later in the season. This translocation can result in nutrient deficiencies
in the leaves unless adequate nutrients are available to the plant during that period.
In general, a fungicide application is not recommended on resistant hybrids.
On susceptible hybrids, a fungicide application may be warranted if disease
is present on the third leaf below the ear leaf or higher on 50 percent of the plants
at tasseling. With intermediate hybrids, a fungicide need only be applied
if conditions are favorable for disease development. Spray if disease is present
on the third leaf below the ear leaf or higher on 50 percent of the plants at tasseling,
and the weather is warm and humid, and the field has a history of Gray Leaf Spot
and/or Anthracnose, and >35 percent corn residue is present.
Previous decisions: Will they come back to haunt you?