Corn: Planting

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Seeding Date
2. Population
   • Seed Spacing to Achieve Various Populations - Table 3-13 (Metric) (Imperial)
3. Planting Depth
4. Updates on Corn: Planting
5. Related links...

Seeding Date

The best yields are usually obtained from corn planted in late April and the first half of May, because the crop is able to use the full growing season. Early planting also results in earlier maturity in the fall, reducing the risk of damage from an early fall frost or adverse weather at harvest. The optimum planting date is on or before May 7 in southwestern Ontario and May 10 in central and eastern Ontario. Delaying planting past the optimum date can result in yield reductions averaging 40 kg/ha per day.

Depending on the total number of days required to plant the farm's entire corn acreage, it is generally necessary to start planting corn well before the optimum date. Producers wanting to plant corn significantly earlier than optimum dates (i.e., April 15-25) should remember that soil temperatures need to reach a minimum of 10°C (50°F) before germination and emergence will occur. The average daily temperature is estimated by taking a temperature measurement around 11:30 a.m. using a 10 cm (4 in.) soil thermometer. If average soil temperatures are at or beyond 10°C (50°F), the soil conditions are favourable, and the weather forecast is predicting average to above-average temperatures, then early planting of at least a portion of the corn crop is recommended. After April 26 (May 1 in areas receiving less than 2,700 CHUs), it is generally advisable to pay less attention to soil temperature and to plant as soil moisture conditions permit.

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Population

The plant populations discussed in this section are suggested final plant stands (see Table 3-13, Seed Spacing to Achieve Various Populations). Since not all seeds emerge, it is necessary to seed at slightly higher rates. When planting early in the season or when the soil is cold, a seeding rate 10% higher than the desired final stand is recommended. When soils are warmer, an adjustment of 5% is sufficient.

1 ha = 2.47 ac; 1 cm = 0.39 in.

1 ha = 2.47 ac; 1 cm = 0.39 in.

In Ontario, corn has commonly been grown at populations of 64,000-74,000 plants/ha (26,000- 30,000 plants/ac). These populations can produce good yields over a wide range of growing conditions without excessive lodging. In recent years, hybrids have been developed that tolerate higher plant densities without excessive lodging or barrenness. Research has shown that when old and new hybrids are grown side by side under very low populations, they yield almost identically. Higher yield responses occur as newer hybrids are grown at higher densities. Much of the historical yield improvement has come from developing hybrids that excel under higher densities. Some of the most recent hybrids report having economically optimum populations of 74,000-86,000 plants/ha (30,000-35,000 plants/ac). Seek out seed company data to fine-tune hybrid management and planting density.

Growers are concerned that increased seeding rates do not always result in greater yield potential. This is a valid concern, particularly on drought-susceptible fields where water availability, not light interception, is almost always the yield-limiting factor. Some savings can be obtained by adjusting populations downward in these situations. Research from the U.S. indicates that the optimum final plant population in the Midwest Corn Belt is 67,000 plants/ha (27,160 plants/ac). These researchers also predicted, based on their work, that for every 9.4 t/ha (15 bu/ac) increase in a field's yield potential (or parts of fields), economically optimal populations increased by 1,112 plants/ha (450 plants/ac).

In Ontario, it is common to aim for higher average final stands than in the U.S. Midwest. The most productive fields should be near the upper end of the plant population range for the hybrids being planted. In shorter-season areas of the province, where smaller-stature hybrids are grown, populations may be under even more pressure to remain high to maximize light interception and optimize yields. Yield increases from increased plant densities have generally been lowest in the warmer regions of Ontario (over 2,900 heat units).

Since lodging is of less concern for whole-plant corn silage, higher plant populations (10%) than those for grain corn have often been recommended. Research from Cornell University indicates that for silage growers who had been adopting ultra-high populations - 111,200-123,500 plants/ha (45,000-50,000 seeds/ac), there were no advantages for any of the hybrids tested to having stands of more than 86,500 plants/ha (35,000 plants/ac). It was also noted that a steady decline in silage digestibility occurred across all hybrids as populations increased. Producers should also note that there is increasing genetic diversity among silage hybrids and that optimum populations may be very hybrid specific.

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Planting Depth

The first rule of corn-planting depth is to plant securely into moisture. However, a few other considerations allow for some fine-tuning of planting depth. Overly shallow planting of corn, that is, less than 3 cm (1.25 in.) deep, even into moisture, may lead to less favourable positioning of the growing point and first nodal roots. This may lead to rootless corn syndrome in some cases and predisposes the seed to greater injury from herbicides. Some soil-applied herbicides require planting depths of at least 3.75 cm (1.5 in.). Coarse-textured soils that dry rapidly at the surface will also be more prone to poor root establishment in shallow plantings.

In contrast, planting deeper at 5-8 cm (2-3 in.), especially early in the planting season when soils are cold, can significantly delay emergence compared to planting depths of 3-5 cm (1.25-2 in.). Where soil temperatures are lower (i.e., early season, cool season, no-till, etc.) and when soil moisture levels are adequate, producers may want to target planting depths around 3.75 cm (1.5 in.). As the planting season progresses and as soils warm and dry, ensure that the corn seed is placed firmly into moisture. In dry soils, planting at depths of 7.5 cm (3 in.) in order to find moisture is often less risky than planting shallower and hoping for rain.

Updates on Corn: Planting

No updates available at this time.

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Related links...

• Corn

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