The objectives of this study were: (a) to estimate the proportions of crop yield change attributable to crop variety improvement, higher rates of fertilization, regional specialization and other crop yield variables and (b) to determine how the relative economic yield level per acre changed over a 20-year period.

The analysis covers major crops on a state, regional and national basis. Based on time-series data, over 80 state crop-production functions were estimated for corn, wheat, oats, barley, grain sorghum, soybeans, flax, cotton and tame hay. Annual state crop yields were considered a function of inherent soil fertility, weather, crop variety improvement, fertilizer application, short-run changes in acreage, and time.