Corn Yield Response to Soil Applied Zinc Sources.

Alluvail soils of the Red River valley in Louisiana are frequently characterized as alkaline in pH and categorized as having high levels of soil test P. The Red River Valley stretches from the Northwest to the Southeast of the state, and is farmed primarily for corn, soybeans, cotton, and sugarcane. Corn producers often report the appearance of visible zinc deficiency symptoms, particularly in the early stages of plant growth, and are requesting updated information on the efficacy, rate, and source of zinc for optimal corn yields. A trial was initiated in 2 locations in 2011 in which 2 sources of zinc (ZnSO4 and ZnEDTA chelate) were surface applied after corn planting but prior to emergence at 4 rates (0, 2.8, 5.6, 11.2 kg Zn ha-1), on soils characterized as having pH 7.5 and soil test P = 50 mg kg-1 (Mehlich III). Parameters measured were soil test Zn, leaf tissue P and Zn at V3 and V8, and grain yield. A Zn application rate of 5.6 kg ha-1 optimized grain yield, with an average yield increase of 2197 kg ha-1 over the zero Zn rate. A lower application rate was required from ZnEDTA to optimize yield. A Zn application rate of 5.6 kg ha-1 was required for soil testing < 1.5 mg kg-1 Zn. The trial will be repeated in 2012.