Good point on the weight, size and compaction problems of the big stuff. Steel tracks have been available for decades for the rice boys. Rubber tracks for combines have been available in the U.S., Europe and Australia since the mid 90's but the costs have been the killer. Rubber tracks were put on some cultivating equipment by an Aussie firm [ Horward.Bagshaw. ] in the late 90's and tested a few kilometres from us. The depth control, measured against an identical wheeled machine was superb. The horse power required, again against the identical wheeled machine was, surprisingly, considerably reduced. The track design and quality, supplied by an outside firm was not up to the job. The tracks literally broke up after being roaded for some 50 kilometres at about 30kph. H.B. also had financial problems at the time and did not go on with the project. There have also been a few 5000_ 6000 litre spray booms tracked here in Oz. We still own the 3'rd tracked Cat imported into Oz. We bought it in ourselves as Cat would not supply to Oz in the late 80's. I am still sold on tracks!