Corn Yield Response to Varied Producer Controlled Factors and Weather in High Yield Environments

Abstract

Much of the corn (Zea mays L.) yield increases in the past five decades can be attributed to the identification and adjustment of controllable factors that limit production. This process must continue if we are to meet the food requirements of the future. The objectives of these experiments were to determine what combination of the producer controlled variables (e.g., N, P, and K fertilization, plant density, row spacing, hybrid, and timing of N application) would give maximum yields under the prevailing climatic conditions in the western Corn Belt. Eight field experiments were conducted in eastern and central Iowa from 1982 through 1984. Treatments varied with location but the treatment ranges were as follows: plant density—20 000 to 36 000 plants/acre; row spacing—20 and 30 in.; N rate—60 to 333 lb/acre; fertilizer P rate—0 to 99 lb/acre; fertilizer K rate—0 to 249 lb/acre; N timing—preplant vs. split (preplant and side dress); plus four different hybrids. Weather had a moderating effect on all but one experiment by either delaying planting or providing severe moisture stress. Mean experiment grain yields ranged from 103 to 178 bu/acre, with the combination of controlled variables giving maximum yields varying with site-year. Grain yields did not respond to fertilizer N rates above the initial rate. Soil P levels were sufficient to produce maximum yields with or without added fertilizer P, and in 1983, added P resulted in a negative yield response. Grain yields responded to fertilizer K rates of 166 and 249 lb/acre in 1982 on plots with soil tests averaging 67 and 91 ppm K, respectively. The rate of 166 lb/acre resulted in grain yield increases in 1984 on plots with soil tests averaging 85 ppm K. The lowest plant densitities, which ranged from 20 000 to 26 000 plants/acre, gave maximum yields in all experiments. The row-spacing variable resulted in a grain yield difference only in 1982 when 20-in. rows showed an advantage over 30-in. rows. Hybrid had a significant effect on yield in all but one experiment. These experiments demonstrate the increased risk to the producer who is striving for high yields but who cannot control or predict the weather.