Sorghum Growth as Affected by Annual Applications of Atrazine

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Abstract
Soil carryover of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] following annual applications to a sorghum [Sorghum bicolor(L.) Moench] monoculture was studied by assessing sorghum yield factors as well as yields of a subsequent bioassay crop of oats (Avena sativaL.). Atrazine applications of 3.4 kg/ha or more increased sorghum injury and rates of 4.5 kg/ha and more increased seed weight and decreased sorghum stand. Sorghum recovered from early atrazine injury and stand loss and generally maintained yields. Rates of 2.2 kg/ha did not reduce sorghum yields even with repeated annual usage. There appears to be little hazard of reducing sorghum yields due to atrazine carryover in the soil from annual atrazine applications at normal rates to a clay loam or silty clay loam soil in eastern Nebraska. However, atrazine carryover will have to be a consideration if the grower plans to rotate to a susceptible crop such as oats.