Nevertheless, the tractor business remained a competitive field, at least for a few decades, and competition helped foster innovations. Tractors themselves got smaller and more lightweight and were designed with a higher ground clearance, making them capable of such relatively refined tasks as hauling cultivating implements through a standing crop. Another early innovation, introduced by International Harvester in 1922, was the so-called power takeoff. This device consisted of a metal shaft that transmitted the engine power directly to a towed implement such as a reaper through a universal joint or similar mechanism; in other words, the implement "took off" power from the tractor engine. The John Deere Company followed in 1927 with a power lift that raised and lowered hitched implements at the end of each row—a time- and labor-saving breakthrough. Rubber tires designed for agricultural use came along in 1933, making it much easier for tractors to function even on the roughest, muddiest ground. And ever mindful of the power plant, engineers in the 1930s came up with diesel engines, which provided more power at a lower cost.

As tractor sales continued to climb—peaking in 1951, when some 800,000 tractors were sold in the United States—equally important developments were occurring on the other side of the hitch. Pulled and powered by tractors, an increasingly wide variety of farm implements were mechanizing just about every step in the crop-growing process, from the planting of seed to the harvesting of the final fruit. In the 1930s one particular type of machine—the combine—began to take its place beside the tractor as a must-have, especially for grain farmers. The combine had been a bold innovation when Hiram Moore developed the first marketable one in the 1830s. As its name indicated, it combined the two main tasks of grain harvesting: reaping, or cutting the stalks, and threshing, the process of separating the kernels of grain from the rest of the plant and then collecting the kernels. Early combines were pulled by large teams of horses and proved about as unwieldy as the first steam-powered tractors. But towed by the powerful new diesel tractors of the 1930s and taking their power off the tractors' engines, combines became the rage. They did it all: cutting, threshing, separating kernels from husks with blowers or vibrating sieves, filtering out straw, feeding the collected grain via conveyor belts to wagons or trucks driven alongside. This moving assembly line turned acre upon acre of waving amber fields into golden mountains of grain as if by magic.