End of Season Test Plot Evaluation:
What Lessons Can We Learn From Drought of 2003?

September 18, 2003  10(24):172-174

Joe Lauer, Corn Agronomist

Harvest is rapidly approaching and with it the close of the 2003 growing season. The grain-filling drought experienced this year has been somewhat unique. In many ways I was surprised to see corn hang-on as long as it did given the length of time no rain was received. In some of the fields yield-checked, we are finding ears with 16-18 kernel rows and 30-40 kernels per row. This indicates good early growth and pollination conditions. But, we also see a lot of space between kernels indicating that kernel size may be lower than typical. It is unclear how kernel size will affect test weight, but certainly corn kernels had trouble filling properly this year. We see the most stress in fields planted later and with longer-season hybrid maturities. We have finished harvesting most of the silage trials with wet yields typical of past years.

Now is a good time to get into your fields to plan harvest and evaluate last year's ‘experiments.' Some new practices work and fit into your management style, others don't. Lessons learned producing this year's crop will help with next year's crop.

Growers need to monitor fields carefully, and plan harvest schedules to begin with fields where stalk and root deterioration appears worst. Below are some things to check in your fields yet this year for timing harvest, and to consider in your plans for next season. Record information. Keep a notebook or computer file. It is difficult to commit things to memory, especially two or three seasons into the future.

Fall Field Scouting

Check for ear-tip fill. Incomplete ear-tip fill is not necessarily bad. If kernels are filled out completely to the ear tip, plant populations are likely too low for conditions. Expect about an inch of underdeveloped kernels at the ear tip if plant populations are at high enough level to optimize grain yield per acre.

Check kernel development on the ear. Look for differences in how well different hybrids have held up to management practices (i.e. herbicide application, irrigation stress, N stress, etc.) and weather stresses. Early stress from weed competition or low N will reduce kernel row number and kernel number per row. Severe heat and moisture stress during the first seven to ten days after pollination will cause kernels at the tip of the ear to abort. Stress around pollination reduces cell division and potential starch fill causing shallow kernel depth and lighter test weight.

Check the maturity of hybrids in your fields and relate back to planting and emergence dates. Following the rate of drydown using kernel milkline is a good way to predict the order fields should be harvested. In a typical year a common benchmark is that fields should be dented by the first week in September. It takes about 25 days to go from dent to black layer (physiological maturity); about 13 days to get to 50% kernel milk and another 12 days to black layer. Kernel moisture at black layer will average 32 to 35 percent. The tightness of the husk, thickness of the seed coat and daily weather conditions influence the speed of kernel drydown. After black layer formation several hard frosts followed by sunny weather with temperatures in the 80's and a slight breeze is the ideal drying environment.

Hybrids differ in the time it takes to reach harvest moisture from black layer. A rough estimate is that 15 to 20 GDUs/point of moisture are needed to lower the moisture from 35 to 25 percent. It takes 20 to 25 GDUs/point of moisture to dry the grain from 25 to 20 percent.

Scout for corn standability. Fields that have lodging problems can be identified and targeted for the earliest possible harvest. Look for visible symptoms and test stalk firmness by pinching the lower internodes with your thumb and forefinger. Healthy stalks are firm and can't be compressed. If a stalk can be compressed or feels soft, it is rotted and is a good candidate for lodging.

Check for rapid "die-down." The lower portion of corn plants in some fields deteriorates rapidly. Lower leaves first appear nitrogen-stressed, then turn brown and die. Other factors such as compaction, dry weather, herbicide injury or root pruning by insects can also cause these symptoms. Some of these plants may be experiencing low nitrogen availability due to losses from leaching and/or denitrification following excessive rain. Nevertheless, in most cases it is more likely due to remobilization of nutrients from the stalk to the grain, a sort of "cannibalism." Cool, cloudy days and warm nights produce low levels of photosynthesis (sugar production) during the day with high rates of respiration (sugar breakdown) at night. When the plant's nutrient availablity is limited due to low photosynthesis, sugars already produced and stored in the stalk are often "moved-out" (translocated) to help fill the ear. Another factor that might be responsible for rapid die-down is the development of pathogens that cause root and stalk rot. Wet soils and cloudy humid conditions favor these diseases. Corn stalks weakened by remobilization of nutrients to the ear are especially vulnerable to root and and stalk rotting organisms.

During combining inventory weed problems. Use a map and list details such as location of broadleaf and grass species, population density of the crop and weed, and response to herbicides. Watch for new weeds. Watch for any weeds that may be developing resistance to herbicides.

Resist estimating yield differences between corn hybrids - measure it. Field variability alone can easily cause apparent differences of 10 to 50 bushels per acre. Make notes bout "ease of combining." Test weight and grain moisture can influence hybrid yield. There are "quickie" measures of potential grain yield, but you shouldn't expect much precision with these measures.

In preparation for next year, assess soil fertility levels by pulling soil samples.

Test Plot Evaluation

Scout for pest problems. Hybrid differences for pest resistance and tolerance should be monitored and noted all season, but will be most apparent in the fall.

Counting dropped ears is a good way to measure hybrid ear retention and tolerance to European corn borers.

Check overall plant and ear height as well as husk conditions. Hybrids with husks that loosen as ears mature generally dry down rapidly.

Check for goose-necked stalks. This is often root pruning caused by corn rootworms. Hybrids differ in their ability to regrow pruned roots.

Be extremely wary of test plots that are not replicated, or only have a "check" or "tester" hybrid every five to ten hybrids. The best test plots are replicated (all hybrids repeated at least twice, preferably three times).

Don't put much stock in results from one location and one year, even if the trial is well-run and reliable. Years differ and the results from other locations may more closely match next year.

Don't over emphasize results from one type of trial. Use data and observations from university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.

Use field days to make careful observations and ask questions, but reserve any decisions until you have seen the "numbers." Appearances can be deceiving.

A few suggestions on how to evaluate test plots:

Walk into plots and check plant populations. Hybrids with large ears or two ears per plant may have thin stands.

Break ears in two to check relative kernel development of different hybrids. Hybrids that look most healthy and green may be more immature than others.

Differences in standability will not show up until later in the season and/or until after a wind storm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.

Visual observation of ear-tip fill, ear length, number of kernel rows, and kernel depth, etc. don't tell you much about actual yield potential. Yield is not a beauty contest. Some "ugly" hybrids are good performers.

Buy hybrids … don't be sold based on fancy result books and plot signs, flags, streamers, caps, brats, etc. Remember safety as you move into the harvest season this year.

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