1.This document is ENH 132, one of a series of the Department of Environmental Horticulture, Florida C ooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date first printed: June 1987; date reviewed: February 1999. Please visit the FA IRS Web site at http://hammock.ifas.ufl.edu .The Institute of Food and A g ricultural Sciences is an equal opportunit y /affirmative action emplo y er authorized to provide research, educational information and other services onl y to individuals and institutions that function without re g ard to race, color, sex, a g e, handicap, or national ori g in. For information on obtainin g other extension publications, contact y our count y Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and A g ricultural Sciences / Universit y of Florida / Christine Ta y lor Waddill, Dean2.Thomas H. Yeager, Associate Professor and James E. Barrett, Professor, Cooperative Extension Service, Institute of Food and A gricultural Sciences, University of Florida, Gainesville, 32611.ENH 132Influence of Iron on Phosphorus Leaching from a Container Medium1 Thomas H. Yea g er and James E. Barrett2NATURE OF WORKA common phenomenon in field soils is that phosphorus (P) binds or chemically reacts with aluminum (Al) and iron (Fe) to form relatively insoluble and immobile complexes (1). However, little is known about the chemical reactions of P and Fe in soilless media, and the influence of Fe on P leaching. The objective of this research was to determine the influence of an Fe amendment on P leaching from a soilless container medium. Columns (2 x 6 inches, 4 x 15 cm) of an incubated (77F, 25C 11% volumetric moisture for 30 days) 2 milled pine bark: 1 Canadian peat: 1 builders' sand (v/v/v/) medium amended with 7 lb/yd (4.2 kg/m) of33dolomitic limestone, 5 lb/yd ( 270 g P/m) of33superphosphate and the equivalent of 0, 1.7, 10.4, or 62.0 oz Fe/yd (0, 64, 384, or 2300 g Fe/m) from either iron33citrate (16% Fe) or iron chelate (ethylenedinitrilo tetraacetic acid ferric sodium salt, FeEDTA, 15% Fe) were leached daily for 21 days with 0.5 inch (16 ml) of deionized water (pH 5.5). Leachate volumes and pH were determined on days 1, 2, 5, 9, 13, 17, and 21. Leachate P and Fe were determined by standard analyses (2).RESULTS AND DISCUSSIONLeachate P on day 1 ranged from 850 ppm for 1.7 oz Fe/yd from iron chelate to 138 and 91 ppm for 10.4 and362.0 oz Fe/yd, respectively, from iron citrate (Table 1).3Leachate P on days 1, 2, and 5 for 10.4 and 62.0 oz Fe/yd3from iron citrate was lower than for iron chelate and on day 21, P concentrations for these rates of iron citrate were 28 and 11 ppm, respectively. The 62.0 oz Fe/yd from iron3citrate resulted in the lowest leachate P concentrations at all sampling times, indicating iron citrate was more effective than iron chelate in reducing P leaching. Leachate Fe concentrations on day 1 for 10.4 and 62.0 oz Fe/yd3from iron citrate were 0.3 and 5693 ppm, respectively. Leachate Fe for 62.0 oz Fe/yd from iron citrate decreased3to 10 ppm on day 21, while leachate Fe remained at 0.3 ppm for 10.4 oz Fe/yd from iron citrate. Leachate Fe and3P concentrations were not directly related to leachate volume or pH that ranged from 4.5 to 5.5. These data indicate that Fe amendments result in decreased leachate P concentrations from a soilless medium. This indicates a chemical binding or complexing of Fe and P, as occurs with many native soils.
Influence of Iron on Phosphorus Leachin g from a Container Medium Pa g e 2March 1999LITERATURE CITED1)Mengel, K. and E. Kirky. 1982. Principles of Plant Nutrition. 3rd Edition. Intl. Potash Inst.,Bern, Switzerland. 2)Rhue, D. and G. Kidder. 1984. Procedures used by the IFAS Extension Soil Testing Laboratory and interpretation of results. Univ. of Fla. Ext. Cir. 596.Table 1. Leachate P levels ( ppm ) from columns of a 2 pine bark: 1 Canadian peat: 1 builders sand medium amended with 5 lb/ y d ( 270 g P/m ) of superphosphate and the e q uivalent of 0, 1.7,10.4, or 62.0 oz Fe/ y d ( 0, 64, 384, or 2300 g Fe/m ) 33 33Da y Leachate, ppm P 0 oz Fe/ y d 1.7 oz Fe/ y d 10.4 oz Fe/ y d 62.0 oz Fe/ y d3 333citratechelatecitratechelatecitratechelatez y 1 826 728 850 138 805 91 644 2 538 467 490 135 435 51 450 5 169 156 138 84 125 21 144 95 86 35 75 15 21 96 3 13 32 38 30 38 28 15 34 17 20 27 21 32 20 13 22 21 16 22 16 28 15 11 17 Iron citrate ( 16% Fe ) ; Iron chelate ( FeEDTA, 15% Fe ) z y