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At several field days this past summer, Paul Jasa, Extension Engineer with the University of Nebraska, demonstrated several openers used for injecting anhydrous ammonia. Paul's focus was on the proper application of ammonia in high residue, no-till farming systems. His objective was for minimal soil disturbance for improved erosion control and better sealing of the ammonia. He used a toolbar equipped with four conventional knife openers, two with coulters and two without, and three single disk openers recommended by Exactrix Global Systems.
In Photo #1 you can see the variety of openers demonstrated. From the left, the openers are:
Rigid C-shank with a knife, leading 20-inch coulter, and trailing notched covering disks
Modified Yetter 2996 B a 20-inch coulter with a narrow profile knife tucked in behind with an added angled sealing wheel (from John Yockey's Aurora Charger)
Standard coil shank with a knife
Exactrix X-16 B a 22-inch coulter with a narrow profile knife tucked in behind and two angled sealing wheels used also for depth control (from Greg Kreikemeir's X-16)
Standard coil shank with a knife and leading 20-inch coulter
Bourgault MRB B a fixed angle 20-inch disk opener with angled closing wheel (from Greg Carlson's split-row planter)
Rigid C-shank with a knife
The multi-opener applicator is shown in Photo #3 operating in soybean residue at about 6 mph. Photo #4 shows the resulting soil disturbance immediately after this demo run, when the wet soil was exposed. Photo #2 shows the resulting soil disturbance after the soil dried from a previous demo run 4 days prior (immediately to the left of the run shown in Photo #4). Both of the knives without coulters, on the rigid C-shank (far right) and on the standard coil shank (behind left tractor wheel), did considerable tillage, destroying residue and leaving a trench with loosened soil exposed to the forces of erosion. While adding a coulter in front of the knives reduced the soil and residue disturbance, the knives still disturbed more soil than the single disk openers used by the Exactrix customers. Most noticeable is the lack of soil disturbance behind the straight single disk openers, the modified Yetter 2996 (second from left) and the Exactrix X-16 (center).
Operating speed in this demo was limited to about 6 mph due to the short length of run. In another demo on irrigated corn residue as if side-dressing in no-till (sorry, no photos available), the single disk openers and the knives with coulters handled the residue quite well with results at 6 mph similar to that of the runs in soybean residue pictured. The knives without coulters again did considerable tillage and had occasional bunching of the corn residue, forming piles when the residue slid off the knives. When the speed was increased to 9 mph, the knives did aggressive tillage, covering a lot of residue, and the single disk openers did very little. When over 10 mph, the shear bolts on the knives without coulters popped from the excessive forces while the single disk openers slid through the soil with minimal disturbance of either the soil or the residue. The knives with coulters in front of them did considerable tillage at the higher speeds and even the coulters themselves threw some soil. Again, the least disturbance was from the modified Yetter 2996 and the Exactrix X-16, both using straight, smooth disks.
Openers designed for minimal soil disturbance should have a smooth, straight blade to cut a slot in the soil. They need to be of sufficient diameter to cut residue while running at placement depth. A smooth straight edge cuts residue more effectively than a rippled edge and does far less tillage. When used, knives behind coulters can slide through the slot with minimal disturbance provided the coulter cuts the soil to the operating depth of the knife. As such, coulters need to be at least 20 inches in diameter, typical for a four-inch operating depth, or better yet, 24 inches in diameter for five to six inches deep so that the knife doesn't do tillage.
By tucking the knife in behind the coulter or by using a slipper foot behind an angled coulter, the soil and residue disturbance can be greatly reduced. Sealing disks or sealing wheels can be used to catch soil thrown by the opener and move residue back over the injection slot. The wheels can also be used to firm the soil, improving the sealing and reducing the chances of erosion.