September 17, 2015 Pat Beaujot
Comparing a Disc Opener to Knife Opener for Big Iron Show
When we started working on the Seed Hawk opener in the early nineties, we had already seen the results of disc and knife openers. In those early days, brave farmers were bringing up disc machines from Washington and other Southern states and they were having trouble getting quick, uniform emergence in our cold, wet soils. As a result, early zero-till wasn’t very successful. Early on, the ZERO was the focus, and the attitude was to have no disturbance at all, but there was very little success with that in prairie conditions. Soon people realized that some type of knife opener might warm up the soil a little bit, and the research that followed certainly supported that.
Impacts Soil Temperatures
In the spring, soil temperatures are different all over the field, depending on the direction that the sun hits it (the slope) or how much straw or snow cover it has had. If you don’t disturb that field at all, and just use a narrow disc opener, the varying soil temperature will cause the seeds to germinate at different speeds and grow at different speeds. The result is non-uniform emergence caused by varying soil temperature.
When we till up that strip of soil where the seed is placed, we turn the soil a bit and, the sun warms that blackened strip. This causes a bit of mineralization of that nice high organic surface soil, which will release some nutrients. All these factors provides a better seed bed.
There are many other things to consider in addition to soil temperature. Knife openers tend to penetrate easier. We can build a lighter frame machine with a knife opener because they don’t take a lot of weight to penetrate. This can be a significant advantage during a wet spring, as you can travel across the ground easier, without causing ruts or getting stuck.
A knife opener provides more consistent soil-to-seed contact in all conditions. If the soil is soft and wet, a disc will push the straw into the furrow instead of cutting the straw. As a result, you will get soil, seed and straw mixed into the furrow, rather than nice clean soil around the seed, and that is important for proper germination and disease control.
In terms of maintenance, a knife opener is my choice for several reasons. A knife opener will work properly even if it is partially worn out. A disc opener can lose its cutting ability if it is worn. The cost to replace knives is relatively inexpensive and not terribly time-consuming. Most knife systems today have a knock-on tip or one quick bolt to replace them. With a disc you are taking off several bolts to remove the disc and, the bearing may need to be replaced as well, depending on its quality. There is a fair bit more time and expense involved in maintaining a disc drill than a knife drill.
Another advantage is that a knife opener causes a small furrow in the ground and there are some advantages to that furrow. In really dry conditions, the moisture might be an inch and a half below the soil surface when we go to seed. If we create a furrow that is 1.5” deep, then plant the seed 0.75” below that, our seed is placed deep enough in the wet soil to germinate even on hot windy days. The plant will also benefit from the shallower placement of the seed (only a 0.75” rather than 1.5-2” required with a disc opener and no furrow). For a crop like canola, if you can plant it at a half or three-quarters of an inch deep in the moisture and it only has to reach that far to get to the sunlight, it is going to survive quite nicely. If you have to plant it at an inch and a half or more with a disc opener to get to moisture, then suddenly that plant has to have enough energy to push its way to the surface, and sometimes that won’t work.