Soybean Yield Response to Foliar-Applied Micronutrients and Relationships among Soil and Tissue Tests

Research is needed to assess the value of soil and tissue testing for micronutrients. This research evaluated the soybean [Glycine max (L.) Merr.] grain yield response to foliar application of B, Cu, Mn, and Zn and relationships between soil and plant-tissue tests at 42 sites in Iowa. Treatments sprayed at the V5-V6 and R2-R3 growth stages were a control, each nutrient applied separately, and their mixture. Soil-test results for moist or dried (40 degrees C) samples (15-cm depth) for B were 0.23 to 1.66 mg kg(-1) (hot-water test) whereas for Cu, Mn, and Zn were 1.6 to 4.2, 31.5 to 128, and 1.2 to 11 mg kg(-1) by the Mehlich-3 (M3) test and 0.28 to 1.83, 3.8 to 42.3, and 0.48 to 15.1 mg kg(-1) by the diethylenetriamine-pentaacetic acid (DTPA) test. Tissue B, Cu, Mn, and Zn concentrations were 24.3 to 41.5, 5.3 to 15.0, 29 to 113, and 24.5 to 47.8 mg kg(-1) in plants and 27 to 62.3, 3.8 to 11, 26 to 88, and 17.8 to 47.3 mg kg(-1) in leaves. Fertilization did not increase yield, sometimes increased leaf concentrations, but oft en increased grain concentrations. Except for Mn, M3 and DTPA tests were related for dried or moist samples (r(2) 0.310.95). Relationships between soil and tissue tests were not significant or poor (r2 < 0.31). With the exception of DTPA tests for Cu and Mn, published soil and tissue sufficiency ranges were too high for the conditions of this study.