Critical Soil Manganese Deficiency Levels for Four Extractants for Soybeans Grown in Sandy Soil

Abstract

AbstractSoil extractants for Mn are often assigned critical deficiency levels based on indirect experimental evidence. This research was undertaken to calibrate four soil Mn extractants for critical deficiency levels using soybeans [Glycine max (L.) Merr. cv. ‘Ransom’]. Two adjacent field experiments were conducted on Olustee‐Leefield sand (Ultic Haplaquod‐Arenic Plinthaquic Paleudult) with soil pH, microelement, and Mn rate variables. Leaf samples taken at the R‐2 growth stage were analyzed for Mn and soil samples were analyzed for pH and extractable Mn by four separate procedures. Critical deficiency levels were determined using the Cate‐Nelson procedure as well as by comparing tissue Mn critical levels with soil Mn levels using a regression method. The latter method was unsatisfactory for determining critical levels except for two extractants for 1 year. Critical deficiency levels based on the Cate‐Nelson method averaged over the 3‐year experiment period were Double Acid—2.6 ppm, DTPA — 0.22 ppm, Mehlich (NH4Cl‐NH4F) — 1.8 ppm, and AB‐DTPA (NH4HCO3‐DTPA) — 0.4 ppm. Leaf Mn vs. extractable soil Mn correlation coefficients were best for the two DTPA‐based extractants, but all four coefficients were similar when soil pH was included in multiple regression equations.