elemental toxicities in hawaiian soils: myths and realities
TRANSCRIPT
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Elemental Toxicities in Hawaiian Soils: Myths and
Realities
Jonathan DeenikAssistant Specialist, Soil Fertility
Department of Tropical Plant and Soil Sciences
Soil Aluminum and Manganese
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Outline• Soil Aluminum
• Mineralogy and chemistry of Al• Al and soil weathering• Al toxicity in Hawaiian soils
• Soil Manganese• Chemistry of Mn• Mn toxicity in Hawaiian soils
• Management Strategies
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Source: http://www.ga.gov.au/education/minerals/images/edexp3.gif
http://www.solarviews.com/browse/earth/earthint.jpg
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Soil Aluminum3 Hawaiian BasaltsEarth’s Crust
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Young Soil
Moderately Weathered
Ultisol
Highly Weathered
Oxisol
(Source: Bohn et al., 2001)
Si:Al+Fe: 2.6 4.5 4.4 0.4
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Al and Clay MineralsSmectite
Unstable under leaching conditions and as pH< 6.0
Brady & Weil, 2004
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Al and Clay MineralsKaolinite
Unstable at low pH, < 5.0Kaolinite has low zero point of charge (pH = 2.0-4.6)Soils rich in kaolinite under leaching environment can be very acidic and release Al3+ into solution
Brady & Weil, 2004
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Al Oxides (Gibbsite)
Source:http://www.icmab.es/multimetox/docs_lectures/lectures_html/Gale_J/img033.JPG
Stable at low pHZero point of charge (pH = 5.9-6.7)Al only dissolves under very acidic conditions
Al and Clay Minerals
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Fe Oxides (Geothite)
Source: www.cnr.berkeley.edu/.../soilmineralogy.html
Stable at low pHHigh zero point of charge (pH = 5.9-6.7)Does not readily dissolve
Al and Clay Minerals
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Silicate clays are unstable under acidic conditions
- Relatively high Si:Al+Fe ratio- Kaolinite releases Al as pH < 5.5
Al & Fe oxides are more stable under acidic conditions
- They have relatively higher zero point of charge so they tend to keep soil pH well above 5.0 as they increase in dominance
• As Si:Al+Fe ratio decreases (more weathered), Al less soluble
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Aluminum Solubility and pH
Al stable as Al(OH)3 down to pH 4.5
Source: Bohn et al., 2001
KCl extractable Al and pH in a Kauai Oxisol
Source: Ayers et al., 1965
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Weathering Intensity and Al Toxicity
Smectite Kaolinite Oxides
Fox et al., 1991
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Weathering Intensity and Al SolubilityVertisol (Lualualei)
Si:Al+Fe = 0.69
Soil Conservation Service, 1976
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Weathering Intensity and Al SolubilityVertisol (Waihuna) under Pineapple
20% Al saturation
Si:Al+Fe = 0.62
Soil Conservation Service, 1976
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Weathering Intensity and Al SolubilityMollisol (Pamoa)
15% Al saturation
Si:Al+Fe = 0.63
Soil Conservation Service, 1976
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Weathering Intensity and Al SolubilityUltisol (Haiku)
Si:Al+Fe = 0.310.35
52% Al saturationSoil Conservation Service, 1976
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Weathering Intensity and Al SolubilityUltisol (Paaloa)
Si:Al+Fe =0.38
86% Al saturationSoil Conservation Service, 1976
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Weathering Intensity and Al Solubility
Oxisol (Lahaina)
- Relatively dry environment
http://ssldata.nrcs.usda.gov/querypage.asp
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Weathering Intensity and Al SolubilityOxisol (Makapili)
Si:Al+Fe = 0.200.12
4% Al saturationSoil Conservation Service, 1976
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Kauai Ultisols with potential for Al toxicity
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Oahu Ultisols with potential for Al toxicity
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Maui Ultisols with potential for Al toxicity
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Molokai Ultisols with potential for Al toxicity
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Hoolehua series and Al toxicity
Si:Al+Fe = 0.54
Al saturation = 37%
Soil Conservation Service, 1976
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Al and Big Island Soils
Hamakua
Puna
Kona
Kohala
Waimea
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Al and Big Island Soils Waimea
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Medial AndisolsWaimea Series - Ustand
Soil Conservation Service, 1976
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Hydrus AndisolsHonokaa Series - Udand
Soil Conservation Service, 1976
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Al and Big Island Soils
UdifolistsPapai
UstifolistsKekake
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Al and Histosols
UstifolistsKekake
UdifolistsPapai
http://ssldata.nrcs.usda.gov/querypage.asp
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Aluminum Summary
At pH below 5.0 Al solubility increasesUltisols most likely to have Al toxicity under acid conditionsSoils acidified by pineapple production may be problematic especially if Si content is high (>20%)Ca deficiency may be the more serious limitationLiming (CaCO3/CaSO4) and/or organic matter inputs alleviate Al toxicity
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Manganese
A mineral in basalt - MnO2, Mn2O3, Mn3O4In solution as Mn2+, Mn3+, Mn4+
Mn2+ is an essential plant nutrient, but at high concentrations it becomes toxicMn2+ concentration depends on pH, O2availability and organic matterMn toxicity depends on:• Soil pH• Oxygen status• Organic matter status
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Critical level
Mn solubility and soil pH
Source: Hue et al., 1998
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Mn solubility Depends on O2 Status
- O2
+ O2
Source: Porter et al., 2004
Oxisol Wahiawa, high Mn
Mollisol, moderate Mn
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Mn solubility Increases with Organic Inputs
Source: Hue et al., 2001
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Soils with Potential Mn Toxicity
Average MnO2 content of soils = 0.1%Oxisols exisiting at low to moderate elevation (200-750 ft) with moderate rainfall (20-60 in/yr)Molokai, Lahaina, Wahiawa (1.5% MnO2) series
Kaolinitic Mollisols and Inceptisols in dry environmentsKeahua (0.4%), Ewa, Paia (1.7%), Hoolehua (1.5%),
kahana series
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Makaweli Soil with Potential for Mn Toxicity
0.98% MnO2 in surface horizon
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Oahu Soils with Potential MnToxicity
Hue et al., 1998
Soil SeriesWahiawaLahainaMolokaiEwaWaialua
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Molokai Soils with Potential for Mn Toxicity
% MnO20.31.49
0.81
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Maui Soils with Potential for MnToxicity
% MnO20.33
0.4
1.38
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Manganese SummaryMn toxicity occurs in soils with relatively dry climate. Mn toxicity increases as pH drops below 5.5.Mn toxicity can occur in wet soils where organic inputs are highManage Mn toxicity with lime, gypsum, water management, and careful attention to organic inputs
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Summary
Tropical soils are not always Al toxicAl toxicity is most common in acid soils with appreciable amounts of Si. As weathering intensity increases likelihood of Al toxicity decreasesIn most of Hawaii’s highly weathered soils Ca and P deficiency are the limiting factorsAl toxicity is managed with lime and organic matter
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Summary
Managanese toxicity may be a serious problem in HawaiiMn toxicity occurs in dry lowland soils with high MnO2 content that have been acidified, don’t drain well, and/or received organic inputsMn toxicity is managed with lime and careful water management