D. Brian Arnall, Plant and Soil Sciences, Oklahoma State University, Stillwater, OK and Apurba K Sutradhar, 1991 Upper Buford Circle, University of Minnesota, Saint Paul, MN
Plant tissue test for mineral concentrations may be an alternative method for fertilizer recommendation where soil testing is ineffective. A study was conducted to evaluate the consistency of nutrient concentrations among growth stages as a tool for mid-season fertilizer recommendation. Canola (Brassica napus L.) tissue samples were collected on three different days of three different growth stages. Also, three sets of samples were collected on each day at morning, noon, and evening. Therefore, nine sets of samples were collected from a single growth stage, a total of 27 sets of samples were collected from all growth stages. The samples were analyzed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), copper (Cu), boron (B), iron (Fe), zinc (Zn), and manganese (Mn) concentrations. The study was conducted during 2012-2013 growing season at Agronomy Farm near Stillwater Oklahoma on Kirkland silt loam (fine, mixed, thermic, Udic Paleustoll) soil. Nutrient concentrations showed considerable variations except for N. Variability in N concentration was minimum between growth stages when compared to other nutrients. Variations in other nutrient concentrations primarily due to temporal variability. Variations in nutrient concentrations in the morning, noon, and evening within a stage were not remarkable. Based on the analysis, we have concluded that except for N, other nutrient concentrations significantly differed between growth stages. Therefore, critical levels for nutrients need to be adjusted for a specific growth stage while making fertilizer recommendation.