What are the primary causes of poor or delayed emergence?

Poor emergence can occur when planting into a dry or wet seed bed when soil temperatures are below 10^°C. Other causes can include soil crusting prior to emergence, herbicide injury, and insect injury or soil-borne disease infection. Delayed emergence is often caused by seed bed temperatures below 10^°C and dry conditions to the point where the seed cannot imbibe enough water for germination.

What impact does soil condition have before and after corn is planted?

Seed beds that are cloddy or have uneven residue levels can prevent good seed to soil contact and can have varying moisture and temperature levels within the seed zone.¹ Soil moisture may not be at a consistent level in the upper soil profile; therefore, planting depth can be critical to ensure that all the seeds have adequate moisture for germination and consistent early growth.

Can the type of tillage used impact a corn stand?

Tillage is used to prepare a seed bed by mechanically reducing weeds and loosening soil which can help with aeration and incorporating soil moisture. Tillage also helps reduce surface crop residue by mixing residue in the soil profile. Tillage operations have evolved over the time to fulfill the specific production requirements of the crop and the producer.

No-Till is when a tillage implement is not used to prepare a seed bed. No-till planters are equipped with row cleaners to remove residue from the planting zone. No-till seedbeds are usually cooler and have higher soil moisture than tilled seedbeds especially when there are large amounts of residue levels left from a previous crop.

Reduced tillage leaves 30% to 70% of the soil surface covered with crop residue. Strip tillage is a type of reduced tillage, in that only an 18-centimeter band is tilled, while at the same time often placing fertilizer 12 to 20 centimeters below the seed slice, where the seed will be in position at planting. During planting, the seed is placed in the tilled band. Strip tillage can be beneficial when soils have large amounts of surface residue that can keep soils cool and wet and delay planting. When strip tillage is completed in the fall, the soil in the tilled strips in the following spring is often drier and warmer, which can help with faster emergence.²

Conventional tillage attempts to incorporate most of the residue, leaving less than 30% of the soil surface covered with residue at planting. Soils can warm faster when crop residue is incorporated, which can aid in emergence especially for early-planted fields.³ Additionally, it allows the destruction of crop residue, which may harbor plant pathogens.

Can excessive soil moisture at planting comtribute to compaction?

Yes. Soil compaction occurs as the result of equipment in the field under wet conditions. Water can act like a lubricant between soil aggregates, forcing them to become tightly packed together. Compacted soils lead to poor root development, limited nutrient uptake and water availability. Surface soil moisture levels should be below field capacity at planting to reduce compaction. Sidewall compaction can occur when wet soils prevent the collapse of the seed trench when the seed opener slices through the soil. This is especially a concern in soils with high clay content. Sidewall compaction prevents the root system from penetrating through the compacted sidewall of the seed slice (Figure 1), limiting nutrient and water uptake. Ultimately, the plant can be more susceptible to drought stress, be unproductive, or may die.

What are potential problems associated with planting corn when soil temperatures are below 10^°C and remain so for an extended period?

When a corn seed is placed in the seed zone, it almost immediately begins to imbibe water and will imbibe about 30% of its weight in water to start the germination process. Under some situations when the water is extremely cold and absorbed by the seed it can result in death of the kernel or developing embryo. This is referred to as cold shock. Cold shocked seeds will be swollen, yet very hard, and in some cases the coleoptile will have emerged. If the seed is killed by a fungal pathogen, it will usually be soft and easily collapsed. The other type of injury that can occur under cold temperatures, is referred to as imbibitional chilling damage (chilling injury) (Figure 2). Chilling injury occurs after the seed has germinated and the mesocotyl has emerged. Cold temperature can kill cells on one side of the mesocotyl and not the other. Mesocotyl cells are rapidly elongating and the cells on the opposite side from the injury continue to grow causing the mesocotyl to cork-screw. ⁴ It is recommended to plant corn when the soil temperature, within the seed zone, is anticipated to be at 10^°C at planting and remain above 10^°C for 48 hours after planting. Other factors, like herbicide carryover injury or soil crusting may cause this type of injury.

What are starter fertilizers and how can they be useful or detrimental for crop establishment?

Starter fertilizer are small amounts of key nutrients such as nitrogen and phosphorus placed in close proximity to the seedling plant. Starter fertilizer can help meet the nutrient demands of seedlings, while the root system is small, and help establish a uniform stand especially when soils have cool temperatures, low phosphorus levels, are sandy and low in organic matter, or high pH. Recommended placement for starter fertilizer is a 5 centimetres by 5 centimetres (2 inch x 2 inch) starter band below and to the side of the kernel at planting. This placement reduces seedling injury (fertilizer burn), especially under dry soil conditions in light or sandy soils (Figure 3). Starter fertilizers are most beneficial when corn is planted into cold wet soils which reduces root growth rate, nutrient mobility, and mineralization (the breakdown of nutrients into plant usable forms).⁵ Starter fertilizers may help increase early growth in corn but not always increase yield potential.

I planted after applying anhydrous ammonia in the spring. Can this stress the emerging corn?

It depends. Planting too quickly after an anhydrous ammonia application could result in root burn. General recommendations are to wait approximately seven to ten days to plant after an anhydrous ammonia application.⁶ However, there is no definitive waiting period as injury to spring-planted seedlings has occurred from fall-applied anhydrous ammonia. Anhydrous applications should be applied diagonally across the field to avoid the potential of placing a corn row directly into a previous anhydrous ammonia knife slot.

Can planting conditions affect seeding rate?

Yes. The seeding rate should be adjusted according to the planting conditions. Early planted corn may require a higher seeding rate for the same final plant population than corn planted under ideal conditions. When planting early in the season or when the soil is cold, a seeding rate 10% higher than the desired final stand is suggested. When soils are warmer, an adjustment of 5% is enough. In Ontario, corn is commonly grown at seeding rates of 69,200 to 88,900 plants per ha (28,000 to 36,000 plants per acre).²

How can planting depth and speed affect corn stand establishment?

Seeds should be planted at a consistent depth into adequate moisture and with good seed-to-soil contact to help establish uniform emergence. Worn or misadjusted planters can have a negative impact on seed depth and seed to soil contact. It is critical for the planter to place the seed at a consistent depth and then cover the seed with firm soil that has good tilth and without large air pockets, to ensure the seed is placed at a consistent depth of 4.45 to 6.3 centimetres. When compared with uniformly early emerged plants, one out of six plants (16.7%) with a two-leaf stage delay in emergence reduced yield by 4%, and one out of six plants with a four-leaf stage delay reduced yield by 8%.⁷ A depth of less than 2.5 centimetres may result in the nodal root system developing too close to the soil surface, which can lead to rootless corn syndrome. Birds and other animals are more likely to feed on shallow-planted seeds. Planting depth and spacing should be checked regularly during planting to ensure proper placement. Plant spacing uniformity and accuracy may be improved by adjusting the planter speed. As speeds exceed 11 kilometres per hour, a conversion to high-speed planting equipment may be necessary to maintain yield potential. ⁸

What measures should be taken for weed control?

Successful weed control is very crucial for economical corn production. Weeds compete for moisture, nutrients, and light during the growing season and interfere with corn stand establishment and with harvest which can eventually reduce yield potential. Good weed control management practices are required in all phases of corn production. Weeds should be controlled before planting by implementing preplant tillage operations, burndown and residual herbicides or a combination of tactics for the crop to establish under weed-free conditions. However, as weeds become larger the effectiveness of tillage or herbicides to control weeds before planting can be reduced. The risk of crop stand establishment issues and yield loss increases if the crop emerges in a dense stand of large weeds. Weeds as small as five centimeters can reduce corn yield potential if they are present at a high density early in the season.⁹ Field scouting is very important to determine weed species and weed density before enacting any plan for weed control. Consult your local agronomist for herbicide recommendations to control the weed species in your fields.

What measures should be taken to keep pest pressure under control?

Soil insects such as wireworm, seedcorn maggot (Figure 4), white grub, and grape colaspis can feed on seed kernels and destroy germinating seeds. The use of insecticide seed treatment can be justified if the producer has a high-risk environment. Fungicide treated seed protects against seedling diseases including Fusarium, Rhizoctonia, and Pythium. In some Provinces, for some insecticide seed treatments, approval is needed on a case by case situation. The producer will need to follow and respect the laws and rules of their province. It is important to find out about local laws before buying treated seed. Ask your agronomist for advice.