combines

Combines, or combine harvesters, are versatile agricultural machines designed to harvest grain crops by performing reaping, threshing, and winnowing in a single pass. The header cuts the standing crop and feeds it into a threshing mechanism, where grain is separated from the straw; the grain is collected in a storage tank while the lighter chaff is removed from the airstream and expelled.

Modern combines are typically self-propelled and integrate the engine, operator cab, threshing system, separator, cleaning system, grain tank, and an unloading auger. The threshing unit dislodges grain from the kernels, the separator removes the grain from the chaff, and the cleaning system uses sieves and air flow to produce a clean grain stream for storage. Residue exits as straw.

Different header designs allow operation on various crops and terrains. Common crops include wheat, barley, corn (maize), soybeans, and rice. Headers vary in width and can be straight, flex, or auger-type; some models are optimized for delicate crops or uneven fields. There are also specialized combines used in rice paddies or sugarcane fields, with adjusted threshing and separation systems.

Origin and impact: The concept emerged in the 19th to early 20th century, with engine-powered machines increasingly adopted in the mid-20th century. Combines greatly increased harvest efficiency and reduced labor requirements, contributing to larger farm sizes and changes in agricultural practices. They require regular maintenance, fuel, and careful calibration to minimize crop loss and damage.