Much is made of the planting process as it relates to field readiness and equipment set-up. As a result, the majority of Ontario corn and soybean fields are planted properly, with all elements in place and under control, and the desired full stand is achieved. Growers are very good at making the best of the conditions and variables that they can control.
Many industry sources cite April 20 - May 5 as the 'sweet spot' for planting dates to optimize yield (this may be a few days earlier for longer-season areas of Ontario, and vice versa for short-season regions). Planting earlier than this window can be successful if conditions are good, and most importantly if trend-line temperatures are forecast to be above normal. If this is the case, the opportunity may be there for increased yields from early planting.
Soil Conditions and Germination Rates
· Seed-to-Soil Contact. Regardless of soil moisture levels, seed-to-soil contact rules the day when it comes to achieving quick, even germination of a crop stand. Seeds with good soil contact can find soil water, even in dry soils. Seeds with minimal soil contact generally have to wait for moisture to come to them, particularly in dry conditions.
· Soil Temperature. Better stated, soil water temperature. The temperature of the seed's first drink of water is absolutely critical to the next two to four weeks of plant development. Generally, soybeans are more sensitive than corn when it comes to this factor. Even if today is beautiful, look at the forecast and relate it to the investment you are putting in the ground.
· Corn Seedling Development begins with germination of the seed at a minimum soil temperature of 46ºF. This is why agronomists recommend planting corn at minimum soil temperatures of 50ºF, especially with early planting as it doesn't take long to lose a few degrees from the required soil temperatures. Once the kernel has absorbed 30% of its weight in water, germination and emergence of the radicle root from the bottom (tip) of the seed corn kernel occurs.
While germination and radicle root (downward growth) begin at 46ºF, development of the sprout components, the mesocoytl and coleoptile (upward growth) do not begin until soil temperatures reach 60ºF. Most of us have seen corn fields that experienced 10 to 14 days of cool temperatures after planting, and found seeds germinated with plenty of radicle root development, but no upward sprouting activity. Many producers will assume a problem with seed quality in this case. However, the reason this is occurring is because soil temperatures hovered above 46ºF for germination, but never reached 60ºF to achieve sprouting and emergence.
However, this same temperature swing dramatically impacts the development of the mesocotyl and coleoptile. A rapid drop in soil temperature, such as those induced by near-frost conditions within two weeks of planting, can result in distorted development of the seedling. This condition is referred to as Cold Water Imbibitional Injury or Chilling Injury, depicted in the photos below.
Symptoms of this injury are corkscrewing of the mesocotyl and coleoptile, leafing out underground, and generally a mottled or twisting of the sprouted seedling as it approaches the soil surface.
Management Options to Optimize Germination & Emergence
· Plant into soils that have achieved and will retain suitable temperatures. Early planting opportunities are often followed by conditions that drop the seedbed temperature below what is required for rapid emergence. Remember the importance of the first drink of water. Seeds planted into soils with temperatures greater than 50ºF within two to three days prior to the onset of cooler conditions may actually have a better opportunity to thrive than those planted within 12 hours of a cold rain. If you have a suitable percentage (20% perhaps?) of your crop in the ground, consider parking the planter if cooler temperatures and rains are forecast within 24 to 48 hours.
· Mechanical activity can increase soil temperature. In some cases, coulter action from the planter by itself can result in a 2ºF - 4ºF increase compared to undisturbed soil. Cultivation may warm the seedbed even further.
· Work the afternoon shift. This is particularly important during soybean planting, if overnight temperatures have been in the low single-digits. Park the planter for the morning, and start during the afternoon when soils have warmed to the required levels. Your soybean seed will appreciate the much warmer first drink of water!
· Check planting depth and seed placement several times across the field - especially important in the first few acres planted. Avoid planting too deep early in the season - 1 ½" - 2" (min.) for corn and 1" - 1 ½" (min.) for beans. REMEMBER - seed-to-soil contact rules the day when it comes to achieving quick, even germination of a crop stand. Stopping the planter to ensure the planter is set right will pay more than any other action during the growing season (same goes for stopping to set tillage equipment).
Remember patience is critical - critical in waiting until your soils are fit, critical in stopping the planter if the forecast is for cold weather within a day and critical in stopping to properly set your equipment.
Early planting opportunities can provide big dividends if the proper investments in genetics, traits, treatments, and cultural practices are utilized. Keeping these points in mind and talking to your PRIDE Seeds seed professional or agronomist regarding the best recommendations for early planting will go a long way to a successful crop establishment.