ESTIMATING PLANT-AVAILABLE MANGANESE IN SELECTED KENTUCKY SOILS1

Abstract

To assess plant-available Mn in soil, 7 extraction methods were evaluated by correlating data for plant Mn with soil test values. Burley tobacco (Nicotiana tabacum L. ''Burley 21'') and flooded rice (Oryza sativa L. ''Blue Bonnet 50'') were grown in the greenhouse on 15 soil types treated with NH4NO3 (448 kg N/ha), NH4NO3 (448 kg N/ha) + lime (to pH 6.8), or NH4NO3 (448 kg N/ha) + ground alfalfa (6720 kg/ha). Weight of dry matter and Mn content were measured at 50 and 60 days after planting for tobacco and rice, respectively. Plant Mn was then correlated with soil Mn extracted by 7 methods, namely, water, 0.1 N H3PO4, 0.01 M CaCl2, DTPA (0.005 M (diethylenetriamine pentaacetic acid), 0.005 M CaCl2, 0.1 M triethanolamine), 0.1 M NH2OH .cntdot. HCl, N NaOAc [sodium acetate] and 3 N NH4H2PO4. The extractions were made on moist soil samples incubated for 10 days at 30.degree. C at field capacity or flooded. Based on correlations between extractable Mn and plant Mn, no significant relationship was detected for any extractant in limed soils, whereas in unlimed soil treated with NH4NO3 or NH4NO3 and ground alfalfa, DTPA, CaCl2, H3PO4 and water gave significant correlations. For tobacco, DTPA gave the highest correlation coefficient. For rice, DTPA, CaCl2, H3PO4 and water gave significant correlation values that differed little among extractants. Adjusting the Ph of DTPA to pH of 6.3 or 5.3 reduced the correlation coefficient from that of pH 7.3. Soil test values for soils extracted at moisture contents of near field capacity were more closely related to Mn concentration of tobacco and rice than values for soils extracted after incubating under flooded conditions for 10 days.