Here is an idea I gleaned from good old youtube.
I was just about to send this old frame to the scrap yard when I found this idea. The most technical part of making the bicycle cultivator is a small bit of welding and cutting steel with an angle grinder.
I had also just replaced my broken lawn mower blade so it was perfect to turn into the chisel, this is where you will need and angle grinder with a cutting wheel and a grinding disc.
The stem I cut so the largest section fit snug into the headtube of the frame and welded it in.
The seat clamp knuckle enables you to tilt the angle of the chisel blade, also the seat post can be moved up or down to suit the users height.
NOTE – this device is for ‘cultivating’ soil that has been previously worked and is not for breaking up hard ground. Yet it is surprisingly easy to push and with not a lot of effort it will bite into compacted soil.