ABSTRACT
Since man began cultivating crops, and even as he collected his food from wild plants, highest possible yield per unit land area has been a major goal. Records of ancient crop yields are few but in Japan” they indicate rice yield of about 1.2 t/ha in 750 A.D., which doubled to about 2.4 by 1900 and has more than doubled since to a current average of 5.6. Records in England 17 indicate average wheat yield of 0.4 t/ha in 1250 A.D., a fivefold increase to 2.2 by 1900 and a further doubling since to a current 4.01. A highly accelerated rate of yield improvement in recent years is indicated for both crops. Similar large corn yield increases of about 2%/year are indicated by current hybrid-variety yields of about 140 bushels/acre as compared to 80 in 1935 for hybrids, which then averaged 20% higher than local open-pollinated varieties. 5 The cited yields for rice in Japan, wheat in England, and corn in Iowa are all for regions of optimal adaptation for the respective crop. Depending upon climate, soil resources, and utilized agricultural technology, current average yields of other countries vary from 25 to 95% of the current yields cited. Averages of some countries are little higher than the cited rice yields for 750 A.D. or wheat yields for 1250 A.D. 6 Crop yields are now documented yearly in such records as the U.S. Department of Agriculture Crop Production Reports and the FAO Production Yearbooks. Readers wanting mean yields of a crop should consult these reports. Further average yields are not cited here because of great variability from crop to crop, year to year, and country to country. 4
