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Manganese Toxicity in a Hawaiian Oxisol Affected by Soil pH and Organic Amendments

Dep. of Tropical Plant and Soil Science, Univ. of Hawaii, 1910 East-West Road, Honolulu, HI 96822

View larger version (37K): [in a new window]   Fig. 1. Chemical structure and common names of the 16 organic compounds used in the soil Mn dissolution study

View larger version (39K): [in a new window]   Fig. 2. Concentration of Mn in the saturated paste extract as a function of soil pH in the Wahiawa Oxisol

View larger version (34K): [in a new window]   Fig. 3. Soybean cv. Kahala response to lime and gypsum applied to the Wahiawa Oxisol. LSD is the least significant difference at 0.95 probability level

View larger version (19K): [in a new window]   Fig. 4. Soybean shoot dry weight as a function of (A) leaf Mn and (B) leaf Ca/Mn ratio grown on the Wahiawa Oxisol

View larger version (45K): [in a new window]   Fig. 5. Soybean response to different Ca and Mg salts (anion effects) added to the acid Wahiawa Oxisol. Standard errors of the mean are drawn on the top of bars

View larger version (27K): [in a new window]   Fig. 6. Soil Mn dissolution as affected by 16 organic compounds (organics). Relative Mn dissolution = 100[(organics-extractable Mn - KCl-extractable Mn)/KCl-extractable Mn]. Experimental conditions: initial pH 4.5 in 0.1 M KCl, 2-h shaking, 80 mg Mn kg-1 soil was extracted by KCl alone

View larger version (28K): [in a new window]   Fig. 7. Ultraviolet spectra of (A) 100 µM hydroquinone in 0.1 M KCl, pH 5.0 with and without 1.00 g Wahiawa soil after different equilibration time intervals and filtration. Note the change from hydroquinone (curve 1) to p-benzoquinone (curves 2–5). In contrast, UV spectra of (B) 50 µM tannic acid in 0.1 M KCl, pH 5.0 with and without 1.00 g Wahiawa soil showed little change in shape but a sharp decrease in absorbance intensity (an indication of polymerization or adsorption) with the reaction time

View larger version (28K): [in a new window]   Fig. 8. Effect of five organic compounds (100 µM) on soil Mn dissolution at different initial pH. Supporting electrolyte: 0.1 M KCl, soil/solution ratio: 1:100, equilibration time: 2 h. Standard errors of the mean are drawn on the top of bars

View larger version (22K): [in a new window]   Fig. 9. Soil Mn dissolution by five organic compounds (100 µM) as a function of equilibration time. Supporting electrolyte: 0.1 M KCl, initial pH 6.0, 1:100 soil/solution ratio. Standard errors of the mean are drawn as vertical bars

View larger version (45K): [in a new window]   Fig. 10. Soybean shoot dry weight and shoot Mn contents as affected by CaCO3, cowpea green manure, and biosolid additions. Numbers on the top of bars are leaf Ca/Mn ratios