Impact of Ozone on Soybean Yield

Field‐grown soybeans [ Glycine max (L.) Merr., cv. Corsoy] were exposed to O 3 for 7 h daily (0900–1600 CST) for 56 d in open‐top chambers. The air in the chambers was either charcoal‐filtered or non‐filtered, with various constant amounts of O 3 added. The randomized block design incorporated four replicates of six treatments: no chamber (0.042 ppm O 3 seasonal 7‐h average); chamber with charcoal‐filtered air (0.022 ppm O 3 ); and chambers with non‐filtered air plus added O 3 to provide concentrations of 0.042, 0.064, 0.089, and 0.115 ppm. A linear reduction in seed weight per plant with increasing ozone dose ( b (slope) = −87.18) was significant ( P = 0.01), and yields were reduced 5, 23, 39, and 52% for the 0.042, 0.064, 0.089, and 0.115 ppm O 3 treatments, respectively, compared with the 0.022 ppm treatment. Significant ( P = 0.01) linear reductions were also noted for filled pods per plant ( b = 184.4), seeds per filled pod ( b = −0.9955), weight per seed ( b = −0.3794), and percent oil content ( b = −12.33). Significant ( P = 0.01) linear increases were noted for unfilled pods per plant ( b = 58.11) and percent protein content ( b = 20.58). A comparison of the open plots with the nonfiltered air chamber plots provided with the same concentration of O 3 revealed no significant chamber effects.