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Atrazine Persistence in a Corn-Soybean Doublecropping System¹

In areas with a relatively long growing season, a doublecropping system of soybeans (Glycine max (L.) Merr.) planted after corn (Zea mays L.) harvested for silage or grain is gaining acceptance. One problem which has arisen involves the potential injury to the soybean crop from atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] residue remaining in the soil after the corn is harevsted. Field studies were conducted during 1977 on an Arrendondo fine sand (Grossarenic Paleudult) at Gainesville, Florida and during 1978 and 1979 on a Tifton fine sandy loam (Plinthic Paleudult) at Jay, Florida to determine the persistence of atrazine in such a doublecropping system. Soybeans were no-till planted at various intervals (4 to 19 weeks) after atrazine (0 to 4.48 kg/ha) was applied preemergence to corn.

Soybean yields were not significantly affected by 1.12 or 2.24 kg/ha atrazine when the interval between corn herbicide application and soybean planting was 8 weeks. An Interval of 10 weeks was required before 4.48 kg/ha atrazine had no significant affect on soybean yield. The yield loss observed with shorter planting intervals appeared to be the result of a reduction in soybean stand. These results indicate that under conditions of warm temperatures, relatively high rainfall amounts, and sandy soils soybeans can be safely planted after corn harvested for silage or grain (approximately 14 and 20 weeks, respectively, after atrazine application) when rates of atrazine normally recommended for annual weed control in corn (1.12 to 4.48 kg/ha) are used.

Key Words: Multiple cropping • Herbicide carryover • Herbicide residue • Zea mays L. • Glycine max (L.) Merr.

² Assistant professor, Agric. Res. Ctr., Jay, FL 32565 and associate professors, Agron. Dep., Univ. of Florida, Gainesville, FL 32611, respectively.

Received for publication August 1, 1980.