on Monday, July 9, 2018
Seed Depth is the topic this week, which may be the most important aspect that I’ve taken away from the ExactEmerge John Deere Planter we ran. Seed Depth can be measured on two levels: Correctness and Consistency. First, we should determine the Correct Seed Depth. Then we must Consistently maintain that Correct Depth.
Why does Seed Depth matter? Seed Depth mainly affects two things: Emergence and Nodal Root Development. There is also some speculation that Seed Depth affects drought tolerance, but we will not focus on this aspect. Emergence can be directly correlated to yield. Later emerging plants end up just adding to competition, which last week I mentioned is detrimental to yield. Late plants cannot yield due to too much competition by the plants beside them, yet they still compete with the plants beside them, bringing their potential yield down as well. Nodal Root Development is another important factor affected by Seed Depth. Nodal roots are ideally 3/4 of an inch under the surface. Nodal Roots provide support for the plant, and if underdeveloped, will result in “floppy corn syndrome” where plants will wilt and fall over. The best way to prevent this is to plant at 2 inches deep, which is typically the Correct Depth in our area.
IRHD will deliver the seed to the Correct Depth, Consistently. To obtain a consistent depth, adequate down pressure must be applied to the row unit so that it rides on the gauge wheels. There are three main options for down pressure on John Deere planters today: Pneumatic, Active Pneumatic, and Individual Row Hydraulic Downforce (IRHD). The other two don’t compare to IRHD.
How does IRHD work? To start with, there are hydraulic cylinders on each row to apply down pressure. Then there is a load cell on every gauge wheel depth adjustment handle. This weighs how much weight the gauge wheels are carrying. For example, let’s say to push the openers into the ground to 2” it takes 100 pounds of pressure. If there’s 125 pounds of weight on the row unit, the gauge wheels will be carrying 50 pounds, which would be considered 25 pounds of gauge wheel margin, or extra weight on the row unit to ensure it maintains consistent contact with the ground. If that row unit enters ground where it would take 150 pounds of weight to get to 2 inches of depth, the row unit will still not be 2 inches deep and the gauge wheels will be carrying zero weight and show a zero-gauge wheel margin. At this time, the system would increase downforce applied by the hydraulic cylinder to bring the gauge wheel margin back up to 50 pounds. This measurement, calculation, and pressure change happens 5 times per second and can adjust by 100 pounds per second. That’s once every five seeds when planting 30,000 at 10 mph.
IRHD and its ability to is very impressive. The maps clearly show wheel tracks from spreading fertilizer or spraying, where applied downforce increased to maintain the correct gauge wheel margin in the compacted tracks. Without IRHD, those rows would have placed the seed well above 2 inches. When running in rough conditions, we could easily see the problem with the ride quality and ground contact readings on the monitor, and easily increase down pressure if conditions allowed, or slow down to alleviate the problem. Another situation we ran into is planting into very hard ground behind a rye field that had been grazed. The IRHD increased down pressure to achieve the desired depth, but it required so much force, the wings of the planter actually were lifting out of the ground, placing seed on top of the ground. The planter was not heavy enough to achieve the desired depth in those conditions. Normally this would have possibly been missed, and the seed just laid shallow. The same thing can be done with IRHD if needed, by just selecting manual and entering the desired down pressure to apply across the whole planter, but the only way to know that was happening with a different planter, would have been to dig seed where it wasn’t able to put it into the ground at the desired depth.
The ExactEmerge with IRHD makes a noticeable difference in the field, and hands down outperforms the planters we ran beside. All these factors come together to affect yield, and this fall, we will be able to see just how much that is.
Below are some good articles about seed depth and emergence: