Impact of ozone on field-corn yield

Abstract

Field corn (Zea mays L.) is the most important agricultural crop in the United States, and the major production areas are subjected to potentially damaging concentrations of ozone (O3). Since no information was available regarding the sensitivity of field-corn hybrids grown in the Midwest, plants of two hybrids ('Pioneer 3780' and 'PAG 397') were field grown in open-top chambers and exposed to O3 (7 h/day seasonal means of 0.015, 0.044, 0.073, 0.100, 0.129, and 0.156 ppm) for 83 days to determine the impact of O3 on grain yield. The air in the chambers was either charcoal filtered or nonfiltered with various constant amounts of O3 added to the ambient air (mean of 0.044 ppm) from 0900 to 1600 Central Standard Time. Also included was a nonchambered plot. A randomized complete block design incorporated three replicates of seven treatments. Foliar injury was noted on some plants at the elevated O3 concentrations but was never more than 5% on an individual leaf. Analysis of variance of the data indicated significant ozone effects on overall grain yield, 100-seed weight, seeds per cob, cob weight, and cob length, for both hybrids. Small reductions in overall yield were due to reduced individual seed weight. Larger overall yield reductions were due to reductions in seed weight and number. Three nonlinear models were tested to describe the responses of the hybrids to O3 and the models were not statistically different from each other. The Weibull survival function was used to test for heterogeneity of hybrid responses, and the responses were found homogeneous. The Weibull model predicted yield losses of 2.6% at 0.06 ppm and 16.3% at 0.10 ppm relative to 0.025 ppm O3. A comparison of the open plots with the nonfiltered air-chamber plots provided with the same O3 concentration revealed no significant chamber effects for any of the seed yield parameters.