• Home
• About this site



• Field Scouting
• Crop Management
• Disease Management
• Disease Images
• Insect Management
• Insect Images
• Weed Management
• Weed Images

Chapter 2

1. Introduction
2. Tillage Systems
3. Populations
• Table 2-1,Seed Spacing to Achieve Various Populations
4. Planting Depth
5. Corn Development
   • Table 2-2,Vegetative Growth Stages in Corn
   • Table 2-3,Reproductive Growth Stages in Corn
6. Fertilizers for Seed Corn
• Guide to Nutrient Deficiency Symptoms
• Table 2-4,Phosphate & Potash Recommendations for Corn
7. Secondary and Micronutrients
8. Soil Organic Matter
9. Crop Rotation
• Table 2-5,Various Rotational Crops and Their Potential Negative Impacts
10. Compaction
11. Irrigation

Introduction

While field corn is grown widely across Southern Ontario, seed corn production is concentrated in the counties of Kent and Essex in southwestern Ontario. The long growing season and highly productive soils help to make consistent high yielding seed corn.

South

Sandy, silt-loam soil, cool spring, warmer fall, lake effect moderates temperatures, later planting, last to harvest, 3200 heat units

North

Black-loam soil with excellent water-holding capacity, less heat, more moisture than West, earlier planting (similar to West), 3300 heat units

West

Sandy soil well drained and pliable, hottest of three zones, earlier planting, harvested first, 3400 heat units

Seed corn production while similar in many ways to field corn can differ considerably. Much of the production practice is determined by the contracting seed corn company i.e. inbred planted, row arrangements and planting timing. However within the production system for that company and its inbred lines, there is room for enhanced crop management.

Tillage Systems

Seed corn is usually grown with conventional tillage systems. The inbred lines that are used in hybrid seed corn production do not tolerate less than ideal emergence conditions well. An evenly emerging corn stand is critical to achieving optimum pollination.

One of the main objectives of secondary tillage is to leave the seedbed as uniform as possible. Avoid fall tillage that leaves the soil too rough for secondary tillage to smooth it out in less than 2 or 3 passes. A fine, firm seedbed is the goal of tillage. However, take care with the seedbed fineness. Soils with low organic matter and poor structure that are left with very fine aggregates are more prone to crust. There is a fine balance between seedbed fineness and the risk of crusting.

Populations

Seed according to the rate and row arrangement recommended by your seed corn company.Table 2-1, Seed Spacing to Achieve Various Populations may be of some assistance in ensuring final stands are adequate.

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, 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.

Corn Development

The vegetative and reproductive growth stages in corn are described in Table 2-2, Vegetative Growth Stages in Corn, and Table 2-3, Reproductive Growth Stages in Corn.

Uniformity of Emergence

Uniform seeding depth is a critical factor in achieving uniform emergence. Uneven emergence affects crop performance, because competition from larger, early-emerging plants reduces the yield potential of smaller, later-emerging plants and interfere with uniform pollination. In field corn, studies indicate that yields are reduced by 5% when half the stand suffers from delayed emergence by 7 days and by 12% when half the population was delayed by 2 weeks. Careful planter preparation may be the single biggest factor in obtaining uniform emergence. Check to see that the planter is operating level and that all discs, depth-gauging wheels and seed-firming devices are up to specifications, aligned and operating at the correct depth or pressure. Preplanting management may also play a critical role in emergence uniformity. If the field is left too uneven, if residue is bunched or if surface compaction has not been uniformly alleviated, even the most carefully prepared corn planter may not be able to deliver.

Uniformity of Spacing

Intuitively, corn plants that are perfectly spaced down the row would seem to have a much better chance to optimize final yields. Uniformity of spacing can be measured by the occurrence of doubles or skips, or can be measured in terms of standard deviation. An absolutely perfect stand, where every plant is exactly 18 cm (7.25 in.) from its neighbour, would have a standard deviation of zero. If plants on average varied plus or minus 5 cm (2 in.) from the desired 18 cm (7.25 in.), then the standard deviation would be 5 cm (2 in.). Dr. Bob Nielsen (Purdue University, Indiana) has conducted extensive investigations into the effects of plant spacing variability on final field corn yield. Research results in field corn indicate that every additional 2.5 cm (1 in.) of standard deviation decreases yields by 0.16 t/ha (2.5 bu/ac). Pioneer research has further supported this conclusion. Interestingly, other research has shown little decrease in yield resulting from spacing variability providing emergence was uniform and populations were identical between compared plots.

Poor planter maintenance or high planting speeds are often identified as the causes of poor within-row spacing uniformity.

• Plants that emerge late, so that they are one or two leaves behind neighbouring plants, will most certainly lower yields relative to a uniformly emerged stand and may even lower yield below those obtained by later planted but uniformly emerged corn. Often these plants behave like “suckers” and will not yield anything, particularly under stressful growing conditions. The lack of yield from these delayed plants is not the full extent of impact — these plants also consume valuable inputs like water, which may negatively affect the other plants nearby.
• Return on investment for planter adjustments such as installing new opener discs, levelling the planter, properly adjusting seed-firming wheels and proper seed-depth placement can be quite high.

Fertilizers for Seed Corn

See Guide to Nutrient Deficiency Symptoms

Nitrogen

Corn responds well to nitrogen, so adequate availability of nitrogen is critical to profitable corn production. Excess nitrogen, however, adds unnecessary expense to corn production, as well as increases the risk of nitrate movement to the groundwater. Follow the nitrogen recommendations from your seed company.

Nitrogen deficiency shows up on the lower leaves of a plant first, manifested as yellowing beginning at the tip of the leaf and proceeding down the midrib. Eventually, the yellow areas will turn brown and die.

In young plants, however, yield loss will occur long before nitrogen deficiency symptoms appear, so yellowing is not a reliable indicator of the need for nitrogen fertilizers.

It is common to see symptoms of nitrogen deficiency in the lower leaves as the plants near maturity, even when there is adequate nitrogen for optimum yield.

Phosphate and Potash

Adequate phosphorus and potassium are necessary for optimum corn growth and yield, although the response to these nutrients is not as evident as with nitrogen. Phosphorus deficiency does not show any obvious symptoms, although phosphorus deficient plants will be stunted and may have a darker green or purplish colour. Potassium deficiency symptoms appear on the lower leaves of the plant first, showing as yellowing and browning beginning at the tip and proceeding back along the outside margin of the leaf. Both of these nutrients will exhibit "hidden hunger", where yields are reduced by a deficiency of one or both of these nutrients even though no deficiency symptoms are visible.

Follow this link for Table 2-4,Phosphate and potash recommendations for corn. For information on the use of this table, or if you do not have an OMAFRA-accredited soil test, refer to the section on Fertilizer Recommendations on page 31 of the Agronomy Guide for Field Crops OMAFRA Publication 811.

Where soil tests indicate that large amounts of phosphorus and potassium are required, the major portion may be broadcast and incorporated in the fall or spring. However, where soil tests show a requirement for these nutrients, a fertilizer containing nitrogen (preferably in the ammonium form) and phosphorus, or nitrogen, phosphorus and potassium should be applied as a starter at planting. All of the phosphorus and some of the potassium may be applied in a band 5 cm (2 in.) to the side and 5 cm (2 in.) below the seed (see Table 2-30, Maximum Safe Rates of Nutrients and for more details on fertilizer application, on page 47 Agronomy Guide for Field Crops OMAFRA Publication 811 ).

Secondary and Micronutrients

Magnesium

Magnesium is plentiful in most soils in Ontario, but a deficiency can occur on acid, sandy soils. The symptoms appear first as yellow striping of the lower leaves. As the deficiency worsens, the upper leaves may become striped while the lower leaves turn reddish-purple.

All soil samples analyzed under the OMAF-accredited soil testing program are tested for magnesium. This test is a reliable guide for determining magnesium requirements.

Dolomitic lime is an excellent source of magnesium. Where limestone is required to correct soil acidity, dolomitic lime should be used whenever the magnesium test is less than 100 ppm.

Few soils that do not need lime will require magnesium. Magnesium application is recommended only if the magnesium test is under 20 ppm. On these soils, magnesium can be supplied either by magnesium sulphate or, if potassium is also required, by sulphate of potash magnesia. Apply 30 kg of water-soluble magnesium/ ha (27 lb/ac).

High applications of potassium can induce magnesium deficiency. For this reason, it is important to monitor soil potassium levels closely and restrict potash application rates to those recommended by the OMAF-accredited soil test. Seed corn is often grown in rotation with tomatoes. High potassium levels are desireable for whole pack tomatoes but may induce magnesium deficiency in corn.

Sulphur

Sulphur deficiency has not been observed in corn in Ontario. The corn-growing areas of the province receive adequate sulphur as acid precipitation.

Zinc

Zinc deficiency occurs on corn in Ontario. Visible symptoms on the leaves are the best indications of deficiency, but soil tests are also useful. Zinc deficiency usually appears as a broad white band near the base of the younger leaves on a corn plant. In severe deficiencies, the entire leaf in the whorl will be white (known as "white-bud"). Response to zinc should not be expected unless deficiency symptoms are quite marked.

When zinc is required, it may be applied to the soil mixed in the fertilizer at rates supplying 4-14 kg/ha (3.5-12.5 lb/ac). The higher rate should be sufficient for up to 3 years. Not more than 4 kg/ha should be banded at planting. Zinc may be applied as a foliar spray at rates supplying 60 g/100 L (0.6 lb/100 gal). A wetting agent should be added. Spray to leaf wetness.

Manganese

Manganese deficiency in corn is rare, although there have been a few occurrences reported on muck soils with high pH in southwestern Ontario. Corn is much more tolerant of low soil manganese levels than soybeans or cereals. Manganese deficiency in corn appears as an olive-green discolouration of the leaves, occasionally with faint striping. Foliar application of manganese is the most effective way to correct a deficiency.

Correct the deficiency as soon as detected by spraying the foliage with 2 kg of actual manganese/ha from manganese sulphate (8 kg of manganese sulphate/ha) in 200 L of water. A "spreader-sticker" in the spray is recommended. If the deficiency is severe, a second spray may be beneficial. When applying micronutrients, take care to first clean out the spray tank of a sprayer that has been used to apply herbicides.

For more fertility and crop nutrition information refer to OMAF publication 611 The Soil Fertility Handbook or contact your seed corn company.

Soil Organic Matter

Soil organic matter is an important component of soil. It is a key part of the nutrient cycle, holding soil moisture and soil structure. The soil organic matter pool in the soil is always changing and is similar to a bank account. Farming practices add or withdraw from the pool or account. Practices such as conservation tillage, good crop rotation, cover crops, manure and other organic material additions and controlling erosion add or maintain organic matter. Excessive tillage and soil loss withdraws from the account.

Seed corn is particularly sensitive to poor soil conditions. Maintain soil organic matter levels through good farming practices to increase the resiliency of your soil and seed corn crop under stressful weather conditions.

Crop Rotation

Crop rotation is an integral part of any crop production system. The greatest benefit to a good crop rotation is increased yields. A well-planned crop rotation will help with insect and disease control, and will aid in maintaining or improving soil structure and organic matter levels. Using a variety of crops can reduce weed pressures, spread the workload, protect against soil erosion and reduce risk. Legume crops in the rotation have become more valuable with the increased cost of nitrogen. Research and experience have proven that a good crop rotation will provide more consistent yields, build soil structure and increase profit potential.

The basic rule of crop rotation is that a crop should never follow itself. Continuous cropping of any crop will result in the build-up of diseases and insects specific to that crop, and cause a reduction in crop yields. The more often that crop has been grown in the field in the past, the greater this impact will be. For example, the practice of growing two or more years of soybeans has become increasingly common or in the past isolation areas were planted frequently to soybeans. Perhaps the greatest impact of back to back years of soybeans in the seed corn production areas of southwestern Ontario has been the accelerated spread of soybean cyst nematode (SCN).

The increased number of years of soybeans in the rotation is also increasing the susceptibility of Ontario's soils to erosion. In fact, the structure of soils in corn-soybean rotations can actually be poorer than soils which are in continuous field corn production. For example, a recent study found that erosion following an intense June rainstorm in first-year corn following 2 years of soybeans was twice as high as following corn, wheat underseeded with red clover or alfalfa. Relatively poor soil structure after 2 years of soybeans not only increased erosion susceptibility, but also reduced soil porosity which resulted in less rain water infiltration. Reduced rain-water infiltration increases the likelihood of erosion risk, yield reducing water ponding and/or soil moisture deficits; all of these effects can reduce crop productivity, particularly in years with weather-related stress.

The greatest benefit from crop rotation comes when crops grown in sequence are in totally different families. The two families are grasses (monocots) and broadleaves (dicots). The grasses include forages grasses, cereals and corn. Soybeans, white beans, alfalfa and canola are examples of broadleaf crops.

The fibrous root systems of cereal crop and forage crops (including red clover) are excellent for building soil structure. Ensuring good soil structure is critical to seed corn establishment. The generally less aggressive growth pattern of seed corn means that it is less tolerant of soil conditions that interfere with emergence and root growth. Studies have shown that the benefits of including wheat, and especially wheat plus red clover, may persist beyond just the following year. Underseeding red clover into wheat resulted in yield increases every year for three consecutive years compared to when red clover was not included in 4-year rotation systems.

In choosing which crop to grow, consider the economics of the entire rotation instead of a single crop in isolation. Also, be aware of any potential insect or disease problems that could affect crops later in the rotation.

Compaction

Seed corn is grown in rotation and it is important to be aware of the potential for compaction through out the crop rotation. Seed corn often seems to be affected more by environmental stresses like dry conditions, poor soil structure etc, than field corn. Compacted soils will tend to stress the plant more. Use good crop management techniques to avoid or reduce compaction

Minimize Compaction With:

• Know your axle load. Know your tires. Run the correct inflation pressure
• Increase tire size and lower inflation pressure
• Duals versus singles should mean lower inflation pressure
• Reduce axle loads
• Timely tillage — avoid wet soil
• Crop rotation

Irrigation

Irrigation of seed corn has not been a common practice in Ontario except with those growers that have irrigation equipment and access to water or in extremely dry years.

However, seed corn production has been adversely affected by dry weather conditions in recent years. Lower yields due to dry weather and the instability this creates in the seed corn industry has led growers to look for methods to help maintain consistent yields of seed corn, ensuring stable supplies of seed to the contracting companies. Irrigation is the logical choice for maintaining seed yields in dry conditions..

Seed corn presents growing challenges that field corn does not. Generally, seed corn plants are smaller and less vigorous than field corn. Root systems tend to be smaller and shallower in seed corn than field corn, which makes it more difficult for the crop to collect water during the summer months. This can limit yield of seed corn. Seed corn also has a higher value than field corn and the payback from irrigation requires smaller yield increases than with field corn.

In recent years there has been irrigation research in Ontario to determine the potential of irrigation in ensuring a consistent, dependable yield. The most recent report states " Properly timed irrigation marginally increased seed corn yields, increased seed kernel weights, accelerated plant growth showing earlier silk and tassel emergence and reduced the incidence of common leaf rust disease". However, the economics of irrigation remain inconsistent due to the production contracts and the variable cost of irrigation. For some growers on light textured soils with low soil moisture capacity, ready access to water and existing irrigation equipment, irrigation may pay in some years. Critical periods for irrigation applications need further refinement for more widespread adoption.