A couple of things to think about this year planting. This is an article I found on planting depth.
Root Establishment and Growth
Around the third to fifth vegetative growth stage of corn (V3 to V5), the crown or nodal roots relieve the seed roots from their responsibilities and will “carry the load” for the corn crop the rest of the season imbibing water and essential nutrients. Regardless of corn seed planting depth, the crown roots will always form ¾ of an inch below the soil surface – even if corn was planted 5 inches deep. The only way this process is disturbed is when corn is planted one inch or less. In these instances, the crown roots are forced to establish closer to soil surface which could lead to inefficiencies in the plant’s ability to establish healthy roots. These plants are also more prone to wind and more likely to lodge come harvest. With fast planter speeds (> 5mph) and rough seedbeds, the likelihood of a smooth planter ride is decreased which means our seed depth may be compromised. Planting 1.5 to 2 inches deep will provide an adequate window of ensuring proper seed depth placement.
Rate of Emergence
The second misconception is that shallower planted corn will emerge quicker than deeper planted corn. An extensive search and even creation of film footage of corn seedling emergence went with little to no success. Instead, a backyard garden study was conducted to investigate the speed of emergence from corn planted at one, two, three, and four inches deep. Four corn seeds were planted at each depth in a heavy clay loam and essentially flooded with water immediately after planting. Soil temperatures were around 70ºF, which was ideal yet the moisture situation was far from ideal. This study revealed that all seeds had emerged within 6 hours of one another at one, two and three inches deep. The four inch deep seeds never emerged. After 2 weeks, no visual differences in height or growth stage were observed among the different depths. The results were shown and evident at the field day. To this Agronomist, 6 hours is not a significant amount of time to state that one inch planted corn emerges faster than three inch planted corn.
Soil Temperature
Soil temperature can drastically influence a seed’s ability to germinate. It is common knowledge that seed germination processes begin when soil temperatures are approximately 50ºF. One would also believe that the deeper into the soil profile, the colder the soil temperature becomes. However, when you inspect the top couple inches, one could argue that there is minimal difference in temperature. Research was conducted to investigate two different depths (0.4 and 2.0 inches) for weed seedling emergence. During this study, the researchers collected soil temperatures in two tillage systems – conventional (figure 1) and no-till (figure 2). The results show minor differences in soil temperature.
Figure 1
Figure 2
Soil Moisture
The only time soil moisture can negatively impact germination is when soils are extremely dry or wet. When soils are dry, the recommendation would be to plant deeper (perhaps even deeper than two inches) until a uniform level of soil moisture can be achieved. Soils that are extremely sandy or variable soils with sandy hills deal with dry soils on an annual basis. The idea is to make sure that all seeds are planted at a level where adequate soil moisture can be reached for proper germination. (Remember that seeds need to imbibe roughly 30-50% of its weight in water to begin germination.)
Summary
By now I hope to have you brainwashed into believing that planting at one inch can be hazardous and will gain no advantage. I’m not recommending planting at four inches deep, but I hope that there are fewer concerns if corn mistakenly gets planted “too deep.” Planting at 1.5 to 2 inches will generally provide the most uniform environment for consistent germination. And every grower knows that high yields begin with uniformity in germination.