The yields are based mainly on the experience and records of farmers, conservationists, and extension agents. Available yield data from nearby counties and results of field trails and demonstrations are also considered. The management needed to obtain the indicated yields of the various crops depends on the kind of soil and the crop. Management can include drainage, erosion control, and protection from flooding. The estimated yields reflect the productive capacity of each soil for each of the principal crops.
Yields are likely to increase as new production technology is developed.
The productivity of a given soil compared with that of other soils, however, is not likely to change. Absence of a yield indicates that the soil is not suited to the crop of the crop is generally not grown on the soil.