Soybean yield trends from 1972 to 2003 in mid-western USA

The increases in crop yield that played an important role in maintaining adequate food supplies in the past may not continue in the future. Soybean ( Glycine max L. Merrill) county yield trends (1972–2003) were examined for evidence of plateaus using data (National Agricultural Statistics Service) for 162 counties (215 data sets) in six production systems [Iowa, Nebraska (irrigated and non-irrigated), Kentucky and Arkansas (irrigated and non-irrigated)] representing a range in yield potential. Average yield (1999–2003) was highest in irrigated production in Nebraska (3403 kg ha −1) and lowest in non-irrigated areas in Arkansas (1482 kg ha −1). Average yield in the highest yielding county in each system was 31–88% higher than the lowest. Linear regression of yield versus time was significant ( P = 0.05) in 169 data sets and a linear-plateau model reached convergence (with the intersection point in the mid-1990s) in 35 of these data sets, but it was significantly ( P = 0.10) better in only three data sets (