Soybean Injury from Triazine Residues in Soil

Plots were planted to corn ( Zea mays L., var. Mo. 880) and treated with 0, 2.5, 5.0, and 10 lb/A of 2-chloro-4-ethylamino-6-isopropylamino- s -triazine (atrazine) or 2-chloro-4,6-bis(ethylamino)- s -triazine (simazine) in 1964 and in 1965. Soybean ( Glycine max L., var. Clark 63) forage yields from soil samples collected in the spring, 1 year after application, were not affected by treatments of 5.0 lb/A or less of atrazine. Yields were reduced on soils collected in the fall (6 months) after application. Following 2 years of treatment, substantial reductions in yields of soybean forage occurred. Soybeans planted in the field following 2 consecutive years of herbicide treatment, yielded similarly to the control plots except when rates of 10 lb/A had been applied.