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Title: EVALUATION OF ROOT GROWTH LIMITING FACTORS IN SPODIC HORIZONS OF SPODOSOLS

Author
item Alva, Ashok
item HUANG, B - WSU-PUYALLUP RES & EXT
item PARAMASIVAN, S - SAVANNAH ST UNIV GEORGIA
item SAJWAN, K - SAVANNAH ST UNIV GEORGIA

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2001
Publication Date: 6/1/2002
Citation: ALVA, A.K., HUANG, B., PARAMASIVAN, S., SAJWAN, K.S. EVALUATION OF ROOT GROWTH LIMITING FACTORS IN SPODIC HORIZONS OF SPODOSOLS. JOURNAL OF PLANT NUTRITION, 25:2001-2014. 2002.

Interpretive Summary: The extent root growth vary considerably in different soils depending on the soil horizon characteristics which could restrict the root growth. Spodosol is a soil type which contains a soil horizon, at about 90 to 120 cm depth, which is acidic in reaction and may contain high levels of aluminum. At low pH aluminum becomes readily available to plant roots and could cause damage to the roots and in turn the whole plants. To evaluate the phytotoxicity of aluminum, it is necessary to measure that fraction of aluminum which is not complexed with organic ligands, i.e. called as the reactive aluminum. The concentrations of reactive aluminum in soil solution from three spodosols ranged from 29.5 to 51.9 micrmolar and 27.5 to 62.7 micromolar for the top soil and spodic horizon samples, respectively. The growth of soybean seedlings was lower in the spodic horizon soil as compared to that in the top soil of the respective soil. The study demonstrates that the reactive aluminum in the spodic horizon was growth limiting in all three soils extracted in this study.

Technical Abstract: Spodic horizon in Spodosols often restricts growth of plant roots. Generally the Spodic horizon is acidic with high levels of aluminum (Al). In this study soil solution Al was characterized in the Spodic horizon and the respective surface horizon (top soil) of three Spodosols in the major citrus production region in Florida. The soil pH ranged from 4.92 to 5.14, and 4.82 to 5.50 in the Spodic and top soil samples, respectively. The modified aluminon analytical technique was used to characterize Al in the soil solution as monomeric Al which includes both organic and inorganic monomeric Al complexes, and as reactive Al (which excludes the organically complexed Al). The organically complexed Al was determined by the difference between the above two concentrations. The concentrations of total Al in soil solutions were measured by the aluminon technique. The polymeric Al was estimated by the difference between the total and monomeric Al concentrations. Further, the activities of different monomeric Al species were calculated by MINTEQA2 thermodynamic speciation model. The reactive Al varied from 29.5 to 51.9 and 27.5 to 62.7 micromolar in soil solutions from the top soil Spodic horizon samples, respectively. The corresponding values for the organically complex Al were 10.3 to 32.5 and 15.6 to 51.0 micromolar, and those for polymeric Al were 11.6 to 54.8 and 25.4 to 46.0 micromolar. The shoot and root dry weights of soybean seedlings were lower in the Spodic horizon samples as compared to that of the seedlings in the respective top soil samples, in all three soil series.