Published online by Cambridge University Press: 12 June 2017
Experiments were conducted at Lincoln and North Platte, Nebraska, during 1967 and 1968 to determine the effect of early preplant applications of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) on sorghum [Sorghum bicolor (L.) Moench ‘Nebraska 505′] and weed yields. Atrazine at 2.24 kg/ha was applied on separate plots preplant and incorporated about April 15, April 30, and May 15, and also preemergence without incorporation about May 17, after sorghum was planted. Sorghum grain yields were highest on plots where atrazine was applied preemergence rather than preplant due mainly to better weed control. Sorghum planted with planter units equipped with furrow openers, set to remove 2.5 to 5 cm of surface soil, had better sorghum stands and smaller weed yields than sorghum planted without removing surface soil. Sorghum population was the lowest following the April 30 atrazine application due to stand loss at North Platte, but grain yields were not significantly different from other preplant treatments since stand loss was compensated for by more heads per plant, larger heads, and larger seed.