S-Triazine Herbicides Combined with Nitrogen Fertilizer for Increasing Protein on Shortgrass Range

Three s-triazine herbicides (atrazine, simazine, and cyanazine) applied annually at 1.1 and 3.4 kg/ha to shortgrass range in northcentral Colorado, consistently increased protein concentration in range herbage for 3 years, 1970-72. Overall, herbage yields were not affected. Spring applications were slightly more effective than fall applications. Atrazine and simazine were about equally effective. However, herbage treated with simazine retained protein better into fall and winter than that treated with atrazine. Cyanazine was the least effective. Increases in protein from the three herbicides were additive to increases from N fertilizer applied at 22 and 45 kg N/ha, except in a drought year. During drought, 3.4 kg of atrazine or simazine combined with 45 kg N reduced herbage yields and yields of protein. The most practical treatment was a combination of 1.1 kg simazine and 22 Kg N/ha. Averaged over 3 years, this combination increased protein concentration 43% and yield of protein 35% in September.