A COMPARISON OF DISC OPENERS AND SEED KNIVES
In the world of no-till farming, growers have a variety of equipment options available. How do you make the choice between a knife opener and a disc opener? Even though there are benefits to both kinds of seeders, most producers prefer knife openers. Here is a comparison of both equipment types to help you make the right decision.
Performance in Crop Residue
Crop residue is the true test of any direct seeding equipment. If your field has a thick straw cover – particularly one that is wet or not finely chopped – a knife opener tends drag straw. This can lead to a buildup of straw around the knives or bunches of straw on top of the furrows. A disc opener is supposed to be the answer to that problem. The disc is designed to cut through the straw instead of pushing it aside. However, disc openers have their own set of problems when it comes to dealing with straw. If the soil is soft or wet, or if the discs aren’t kept sharp, the disc opener will fold straw and push it into the furrow. If the furrows aren’t kept clean and free of straw, you could risk introducing disease or slowing the germination rate.
Most farmers agree that thoroughly cutting the straw with a combine is essential no matter which type of opener you use. Crop residue must be trimmed short, well chopped, and evenly distributed over the field. However, the disc opener can still push even the finest bits of crop residue into the soil, whereas a knife opener tends to leave a clean furrow on a properly prepared field.
The Impact of Soil Temperature on Seed Emergence
One of the challenges growers must overcome is cold, wet soil. Slopes, crop residue and other factors can cause different soil temperatures all over a field. Since disc openers do not disturb the soil at all, the growers using them often experience uneven seed emergence. Knife openers solve those problems by creating a blackened furrow that warms evenly, much like a conventionally tilled field. In fact, a study conducted by David Rourke from Minto, Manitoba proved that furrows created by knife openers were ten degrees warmer than disc opener furrows. Even though a knife opener does create some soil disturbance, it only disturbs the soil above the seed bed. The minimal disturbance also comes with some advantages: it causes a small amount of mineralization that enhances the seed bed, and it creates an area for water to collect during dry weather.
Purchasing and Maintaining Your Equipment
When it comes to price and maintenance, most growers prefer knife openers to disc openers. A disc opener has more moving parts and more weight, meaning that the initial purchase price will be higher. Knife openers will work just fine even if the knives are worn, while a worn disc opener loses the ability to cut through heavy soil and straw. When you need to change a disc, there will be several bolts to undo, and you may need to replace the bearing if it is worn. Knives are easily replaced by either tapping the old knife out or taking out one bolt. Replacement discs and bearings also tend to cost more than replacement knives.