Kategorie der abstrakten: Erdkunde

operation-planting, en­riching the soil, cultivating, spraying, killing weeds, harvest­ing the ears, removing the thick natural wrappings, shelling the kernels from the long cobs on which they grow, and cutting the stalks. Because of this extensive use of machin­ery, the average farmer can cultivate as many as 140 hectares and care for a large herd of livestock with no more help than perhaps a son who spends several hours a day in school. On a Corn Belt farm, the most impressive buildings are the large barns and machine sheds which may dwarf the farmer's house itself.

Farmers first began to keep reliable records of corn pro­duction in 1866. Between 1866 and 1939, the corn yield in the United States averaged between 700 and 1,000 liters of shell­ed grain per hectare. Suddenly, in 1940, it began to increase greatly each year; by 1948, it was about 1,500 liters per hectare; and, by 1972, it reached about 3,400 liters per hectare. (The highest recorded yield is about 7,000 liters per hectare, produced in the State of Iowa.) Such a vast and rapid change in the most basic crop represents a real agricul­tural revolution.

This has been a quiet sort of revolution, however, because the chief difference between the older corn agriculture and the new is simply that the farmer plants a different kind of seed. Instead of saving the best ears from each year's crop for the next year's planting, the traditional method, the farmer now buys new seed every year. The increased value of the crop more than pays for the extra cost.

Corn grown from the new kinds of seed is called a ,,hy­brid”, that is, a corn which results from the mating of differ­ent types of the same grain. Different kinds of hybrids are developed for such basic qualities as higher yields, stronger stalks and hydrotropic roots. As with other grains, different strains have been developed for different soil and climate conditions and for different purposes. For instance, some contain twice as much oil as ordinary corn; others are rich in certain minerals.

Producing hybrid corn is a lengthy process which must be done by hand, during 12 or more years of crossbreeding among different varieties. This process, difficult and com­plex as it is, is simple compared to the job of discovering that new kinds of corn could be developed, or to the job of discovering how to develop them. With other grains, all or nearly all the plants are like the parents. But corn is different. American plant scientists began working on the problem of controlling corn qualities very early in the 2Oth century and it was only after many years of trial and error that they were able to master the theory and practice of growing hybrids.