The first self-propelled combine was developed in Australia in 1938, incorporating tractor and harvester in one, and improvements have been steady ever since. Today, the most impressive of these grain-handling machines can cut swaths more than 30 feet wide, track their own movements precisely through Global Positioning System satellites, and measure and analyze the harvest as they go. They are in no small measure responsible for a 600-fold increase in grain harvesting productivity.

The same basic combine design worked for all grain crops, but corn required a different approach. In 1900 corn was shucked by hand, the ears were thrown into a wagon, and the kernels were shelled by a mechanical device powered by horses. The first mechanical corn picker was introduced in 1909, and by the 1920s one- and two-row pickers powered by tractor engines were becoming popular. Massey-Harris brought the first self-propelled picker to the market in 1946, but the big breakthrough came in 1954, when a corn head attachment for combines became available, making it possible to shell corn in the field. The increase in productivity was dramatic. In 1900 one person could shuck about 100 bushels a day. By the end of the century, combines with eight-row heads could shuck and shell 100 bushels in less than 5 minutes!

The hay harvest also benefited from mechanization. In the 1930s mechanical hay balers were at work, but the process still required hand tying of the bales. In 1938 a man named Edwin Nolt invented a machine that automated bale tying, and the New Holland Manufacturing Company incorporated it into a pickup baler that it began marketing in 1941. As in the case of the combine, self-propelled versions soon followed.

Soon just about anything could be harvested mechanically. Pecans and other nuts are now gathered by machines that grab the trees and shake them, a method that also works for fruits such as cherries, oranges, lemons, and limes. Even tomatoes and grapes, which require delicate handling to avoid bruising, can be harvested mechanically, as can a diverse assortment of vegetables such as asparagus, radishes, cabbages, cucumbers, and peas.