Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Soybeans, Glycine max (L.) Merr., cv. 'Centennial', grown on Iberia silty clay (fine, montmorillonitic, thermic Vertic Haplaquoll) responded to foliar-applied Mn (0.2 and 0.4 kg ha$\sp{-1}$ as Mn chelate, 12% Mn) and soil-applied Mn (15.3 and 30.6 kg ha$\sp{-1}$ as MnSO$\sb4\cdot$3H$\sb2$O, 27.3% Mn). Mn deficiency symptoms were corrected but reappeared in foliar-treated plots within three weeks. Symptoms disappeared following a soaking rain but reappeared as soil dried. A greenhouse investigation evaluated the effects of 12 levels of soil-applied Mn ranging from 0 to 20.5 mg Mn kg$\sp{-1}$ soil as MnSO$\sb4\cdot$3H$\sb2$O, 27.3% Mn, on growth of soybeans. Mn deficiency symptoms appeared in plants when the concentration of Mn in leaves + stems was $\leq$16 mg kg$\sp{-1}$. Nodule activity trended toward a maximum value of 445 nmoles ethylene evolved hr$\sp{-1}$ plant$\sp{-1}$ at 12.3 mg Mn kg$\sp{-1}$ soil. A greenhouse investigation evaluated effects of soil-applied Cu, Zn, Fe, Mn, and P on growth on Centennial soybeans. Dry matter yield tended to increase for treatments in the order: Zn $<$ control $<$ Fe $<$ Cu $<$ Mn $<$ P. Phosphorus did not correct symptoms of Mn deficiency. Zinc was not deficient at a DTPA-TEA-extractable level of 0.5 mg kg$\sp{-1}$. Soil Mn was separated into chemically different fractions by sequential extractions. Order of Mn fractionation was water-soluble, N NH$\sb4$OAc-exchangeable, DTPA-TEA-chelatable, easily-reducible, organically-bound, oxides of Mn, Mn associated with amorphous Fe oxides, Mn associated with crystalline Fe oxides, and residual Mn from HClO$\sb4$-HF-HCl digestion. Two annual soil applications of Mn in the field increased Mn concentrations in each fraction except crystalline Fe oxides and residual. Particle size distribution was 10% sand, 42% silt, and 48% clay. X-ray diffraction analysis showed smectites comprised 77% of the clay fraction. Mn deficiency may be found in a soybean cultivar sensitive to low soil Mn levels growing on a moderately old Mississippi River floodplain soil. Conditions associated with Mn deficiency include: (1) moderately acid to alkaline surface horizon and increasing pH with depth, (2) high exchange capacity and base saturation exceeding approximately 70%, (3) DTPA-TEA-extractable soil Mn $\leq$ 3.0 mg kg$\sp{-1}$, (4) soil organic matter $>$ 2.3%, (5) concentration of Mn in top, mature trifoliolate tissue $\leq$ 14 mg kg$\sp{-1}$, (6) leaf tissue Fe:Mn ratio $\geq$ 3.4 and (7) predominantly dry soil conditions.