Disc Harrow weight is mostly in the pans and axles, not the hollow box frame. Hence pan diameter is the key metric for Disc Harrow ability to penetrate.
Notched pans aid penetration. 9" pan spacing aids penetration. However, pan diameter is key.
( Pan thickness is relevant too, but this data is impossible to find for assembled Discs because of pan taper. However, pan thickness is expressed indirectly as part of total Disc Harrow weight. )
Monroe Tufline in photo has 20" diameter pans. Over land that is tilled annually, meaning soft soil, I must run
L3560 tractor at full throttle in HST/MED/4-WD to maintain four miles per hour, required for good soil mixing. Not enough weight bearing on each pan for Primary Tillage, but good for Secondary Tillage with one pass. Unusually, perhaps unique with Tufline, 9" pan spacing on front/cutting gang, 7-1/2" pan spacing on rear/smoothing gang.
An OFFSET DISC is specifically designed for Primary Tillage. Offset Disc requires a heavy, powerful tractor.
I use a 12" moldboard plow for occasional Primary Tillage, most frequently establishing or renewing fire breaks. Infrequently I renew compacted pasture with the plow.
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