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We have had a long and cold winter. The arrival of spring has many growers eager to get into the field. Planting too early, however, can have a negative impact on yield. It is important to plant according to soil temperature and moisture conditions rather than the calendar.
Corn plants require some key ingredients to germinate and emerge uniformly in order to maximize yield potential. Besides adequate and uniform seed to soil contact and surface soil free from crust/compaction, there are some seasonal components that should be considered at planting.
Adequate and uniform soil temperature. Corn and soybeans will germinate and emerge slowly and unevenly when soil temperatures are less than optimal. The optimal soil temperature for corn is 50° F and 55 to 60° F for soybean. Under cold soil conditions, emergence can easily take up to 4 weeks. When soils warm to the mid-50s, corn emergence can occur in as little as 5 to 7 days. Planting into soil at temperatures below the optimum can cause seeds to remain dormant and become more vulnerable to diseases, insects, and animal predators.
Adequate and uniform soil moisture. Simply defined as not too dry and not too wet – most growers know what this looks and feels like in their respective fields. Uneven soil temperature and soil moisture in the seed zone can be caused by: variable soil characteristics (texture, color, drainage, residue), tillage patterns, and uneven seeding depth.
Figure 1. Emergence problems in corn due to soil compaction. Photo courtesy of J. G. Davis, Colorado State University, Bugwood.org.
Seedbed preparation. Tilling fields when soil is too wet can cause soil compaction, which can result in decreased seedling germination, and restricted root growth and nutrient uptake (Figure 1). The majority of soil compaction takes place when equipment passes through a field. Consider staying out of the field if soil sticks to the tires or if equipment is leaving tracks deeper than 1 inch.
Planting depth. Soil temperature and moisture factor into planting depth. Corn seeds should be planted around 1.5 to 2 inches deep when soil moisture is adequate. Planting shallower than 1.25 inches can result in rootless corn or root lodging and can also increase the risk of injury from some soil applied herbicides. If soil is dry, corn can be planted deeper into moisture, at around 3 inches. Recommendations for soybean planting depth range from 1 to 1.75 inches deep and no deeper than 2.5 inches.3 Deep planting provides stable moisture and temperature conditions to the seed, although planting too deep can burn energy needed later by the plant and inhibit emergence in stressful situations, such as soil crusting and compaction. Planter operators should regularly check for proper planting depth and make adjustments as field conditions change.
Germination and emergence issues. Waiting for optimal soil temperatures and conditions may help avoid chilling injury, disease, lack of oxygen to the seeds, and restricted plant growth, which can all lead to poor emergence. However in some instances, such as a late spring frost, injury may be unavoidable. Although it is important to plant within the acceptable planting window for the region and crop, rushing to plant in poor conditions can lead to yield-reducing problems later.
Imbibitional chilling injury. Planting into wet soils with a temperature below 50° F may result in chilling injury during germination. Within the first 24 to 48 hours after planting, corn kernels imbibe 30% of their weight in moisture before germination can begin.1,2 Cold water absorbed from rain or melting snow can cause cell membranes to become rigid and rupture. Evidence of this can be found in swollen kernels that fail to germinate, aborted radicles, and delayed seedling growth.
Figure 2. Deformed mesocotyl elongation due to early planting into cold soils.
Cold soil injury. Cold soils and/or wide fluctuations in soil temperature throughout the day during the emergence process can cause cold soil injury. This can be observed as seedlings leafing out underground, deformed mesocotyl elongation or corkscrewed mesocotyls, and stunting or death of the seminal root system (Figure 2).
Such damage may limit or cease nutrient uptake, restricting normal development of the mesocotyl and coleoptiles, as well as allow for soil disease and pest entry. If the coleoptile and mesocotyl are missing or broken off, damage is fatal. Seedlings with coleoptiles and mesocotyls intact may have new leaf development and resume normal growth when temperatures warm and fields dry.
1 Nielsen, R.L. 2000. Corn growth & development: what goes on from planting to harvest? Purdue University AGRY-97-07. 2 Nielsen, R.L. 2012. Seeding depth considerations for corn. Purdue University. www.agry.purdue.edu 3 Specht, J., Rees, J., Glewen, K., and Grassini, P. 2014. Soybean planting depth: Consider planting deeper. University of Nebraska- Lincoln Crop Watch. http://cropwatch.unl.edu. Web sources verified 03/26/2015. 150326133456