By Kirk Reese, Agronomy Research Manager, Pioneer Hi-Bred International
When considering corn planting for 2012, one certainty is that the growing season will be different than past growing seasons. However, there are some tactics, including planting at the proper depth, that will help overcome weather challenges in the crop.
Corn planting depth is easily measured shortly after emergence. Taking care to dig up as much of the plant as possible, the distance between the growing point, also known as the first node or crown, and the soil surface is usually three-quarters of an inch deep when planted at recommended planting depths. Measuring the mesocotyl, the area between the seed and the growing point, then adding three-quarters inch, will determine planting depth in the soil. Under ideal conditions, corn can emerge in a week to 10 days. Under more stressful conditions, such as wet soils or extended periods of temperatures below 50 degrees, corn may take up to three weeks to emerge.
In general, recommended corn planting depth ranges between 1.5 to 2 inches below the soil surface. Seed-to-soil contact is maximized when corn seed is planted at the recommended depth. Remember that corn seed must imbibe (take up) 30% of its weight in water before germination can occur. Also, temperatures tend to stabilize at this range, which allows for more uniform emergence of corn plants early season. It is vitally important for a corn plant to develop its first nodal root system, which when planted at the recommended depth occurs approximately three quarters of an inch below the soil surface. These are the first set of corn roots that transition the corn plant from using seed reserves at germination to utilizing water and soil nutrients for continued growth and development. Shallow corn planting at a depth less than 1.5 inches can lead to unintended consequences such as “rootless” corn. This is where large fluctuations in temperature and moisture have a negative effect on nodal root development and can result in early root lodging, stand loss and ultimately reduced yield.
Conventional wisdom suggests that planting at more shallow depths allows the seed to germinate in less than ideal soil conditions, especially when planting early, and that speed of emergence is important in soils that tend to crust. During 2010, Pioneer Hi-Bred agronomists conducted a planting depth study with a corn hybrid (Pioneer Brand 35F44) planted three-quarter and 2 inches deep at the OARDC Northwest Station near Custar. Results were that stand establishment, early growth and uniformity were greater in the plots planted 2 inches deep. Also, corn plants planted at 2 inches were a full leaf collar stage ahead in development when compared to corn plants planted at three-quarters of an inch.
Recognizing the need for further research on this practice, Peter Thomison, corn Extension specialist, and Pioneer collaborated on a more intensive study investigating planting depth interactions. Although this research is ongoing, 2011 results confirmed that yield levels of corn planted at three-quarter-inch depths were less when compared to deeper planting depths of 1.5 and 3 inches. These results are thought to be attributed to a greater percentage of non-uniform “runt” plants and overall stand reduction in the shallow planted treatments, due to increased exposure to rapid warm and dry conditions encountered in early June.
Other corn planting recommendations include targeting optimum economic seeding rates based on yield potential of each field. The newest hybrids on the market today are bred to respond to increasing plant density. Since most seed corn germination is typically around 95%, overplant to compensate for 5% stand loss.
It is important to check planting depth in every field and in areas planted at full operating speed. Soil types, planter settings, residue cover, crop rotation and tillage practices all impact planting depth.
Slower planting speeds typically result in better stand establishment, uniformity and hitting the target seeding rate. Above all, please stay safe this season. Planters and tractors are inherently dangerous to operate and there is no field worth planting at the risk of injuring yourself or someone else.