Early Season Stresses in Corn
May 02Early Season Stresses in Corn
Various stresses can impact corn performance in the germination, emergence and early growth windows. Cold soil temperatures can delay the germination process; in some cases when the first water to be imbibed by the seed is very cold, it can damage the normal germination process. 10 degrees Celsius (50°F) is the minimum soil temperature for activity to take place in the seed. Germination activity is minimal below this temperature. As a general rule, there is no need to wait until soil temperatures are consistently above 10°C; if the soil is fit and the optimal planting window (April 25 to May 10) has arrived, then growers are encouraged to plant. The one caution is to avoid planting when extremely cold water is more than likely to be taken up by the corn seed in the 24-48 hour window after planting. This could occur if planting immediately precedes a sudden drop in temperatures and/or snow fall or freezing rain event.
On average, emergence requires approximately 180 CHU to be accumulated. If we look at the recent temperatures and project out to May 15 for Guelph, the CHU total only gets to about 178. So at these temperatures, emergence will be a relatively slow process.
What to do?
- Although we agonize over the problems that haunt us from planting corn too shallow, this forecast will not be favourable to those who plant deeper than necessary. Ensure seed is in moisture and at least 4.4 cm (1.75 inches) deep, but pushing it to 6.4 cm (2.5 inches) this year may cause unnecessary delays in emergence.
- High residue situations will reduce soil temperatures so if row cleaners are an option, try to leave the row zone as residue free as possible.
- Cold soils and cold water uptake by the seed can reduce stands, so increasing seeding rates (i.e. up rates by 2,000 seeds per acre) can be beneficial.
- Avoid planting right up to a cold front, i.e. when evening temperatures are dropping below 3°C (37°F) in your area.
Depending on how long it takes corn seeds to emerge and the amount and intensity of rainfall, soils may form a crust which makes emergence more difficult. There are a few important reminders about dealing with crusting soils and poor emergence.
- A range of tools can be used to bust up crusted soils (crow foot packers, rotary hoes, harrows, vertical tillage units, etc.). Often there is no better strategy than to try one and see if it does the job, if not, try something else.
- Early is almost always better – if you suspect a soil crusting problem and you are going to use a rotary hoe – don’t be late. Once the crust has become overly hard, you will wish you had been to the field two days sooner.
- Can I permanently damage the emerging corn shoot? The coleoptile or spike is the first structure to push towards the soil surface. On occasion, your crust busting efforts may damage the tip of this structure. Providing the damage is isolated to the tip (i.e. 0.6 to 1.2 cm; ¼ to ½ inch) of this coleoptile, the growing point will not be damaged and emergence will continue normally.
The first leaves on a corn plant can go through phases where leaf colour is far from the desired green. One of the more obvious is when leaves take on a purple colour. This purple colour is a result of a buildup of anthocyanin pigment, which is a sugar containing molecule in the leaf tissue. This can have several causes:
- Phosphorous deficiency in the soil
- Restricted root growth from soil compaction caused by wheel traffic, sidewall compaction or tillage in wet conditions
- Restricted root growth because of excessively dry soils
- Cold temperatures and/or extreme fluctuation in temperatures that stresses the plant’s photosynthetic system
In most cases, warmer temperatures and precipitation will contribute to the plant returning to a normal colour. In rare cases, if the purple colour persists into the season then correction of low soil test P or compaction issues will need to be a priority.
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