While giant pieces of machinery are the Cadillacs of the farm-implement business, the portion of the market that's growing most quickly is at the other end of the size spectrum. Under-40 horsepower tractors now make up 53% of the North American tractor market while 20- to 30-horsepower tractors represent nearly one third of all tractors sold. This market grew by 13% last year and by 73% over the past five years, according to the industry trade organization, the Association of Equipment Manufacturers. The people doing the buying aren't really farmers. They're mostly baby boomers with three acres and a dream. Tom Sieper, Kubota Tractor Crop. product manager, says "they're doctors, lawyers and bankers who want to get back to their roots." Japan-based Kubota Tractor sells more sub-compact tractors in the United States than any of its competitors, although Agco Corp. just launched a new line aimed at contractors and landscapers, and Deere & Co. has been pushing its new steering mechanism, which it claims can make mowing go 40 % faster. Kabuto's best-seller is a 23-horsepower, diesel-fueled tractor with a mower as standard equipment, but sundowners, as Sieper calls them, also can add a small front-end loader and a backhoe. Fully equipped, the tractors cost about $18,000 The key to success, according to Sieper, is ease of operation -- no tools required to attach accessories. The parts just snap on and off. "You can look good driving one of these things without being either a farmer or a mechanic. And they shine up real pretty so they look good next to the Lexis."