Basic Concepts in Soil Fertility Jonathan Deenik Assistant Specialist, Soil Fertility Department of Tropical Plant and Soil Sciences

Outline • Soil as a Nutrient Reservoir • Organic Matter • Soil Acidity • Liming • N and P • Soils of Hawaii

Soil Plant Relationships

Havlin et al., 2005. Soil Fertility and Fertilizers

Idealized Soil Composition

50% Solids

45% Mineral

25% H2O 25% Air

5% Organic Matter

50% Pores

Clay is Where the Action is! •Clay Properties: Microscopic size (20%) Liming (CaCO3/CaSO4) and/or organic matter inputs alleviate Al toxicity

Soils with Potential Mn Toxicity z z

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

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Kaolinitic Mollisols and Inceptisols in dry environments Keahua (0.4%), Ewa, Paia (1.7%), Hoolehua (1.5%), kahana series

Manganese Toxicity z

z

z z

Mn toxicity increases as pH drops below 5.5. Reducing conditions (saturated soils) increase Mn toxicity Fresh organic inputs increase Mn toxicity Manage Mn toxicity with lime, water management, and careful attention to organic inputs

Liming is Important z

•

To raise pH - Reduce existing/potential toxicities - Increases P availability - pH range 5.5 - 7.0 - Liming can be expensive because soils are buffered (clay content and OM) To supply Ca - Highly weathered soils are almost always deficient in Ca

Correcting Soil Acidity is Costly

Brady & Weil, 2004

Correcting Soil Acidity is Costly Al3+ + H2O

Al(OH)2+ + H+

Liming Reactions: CaCO3 + H2O

Ca2+ + HCO3- + OH-

OH- + H+

H2 O

HCO3- + H+

H2CO3

Al3+ + 3OH-

Al(OH)3

Liming

Tons CaCO3 per Acre

Uchida & Hue, 2000

Nitrogen

http://www.bettersoils.com.au/module2/images/27.gif

N Mineralization z

Mineralization: Decomposition of soil organic matter by soil microbes releasing inorganic N in the process.

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Heterotrophs use organic molecules as source of energy

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• •

Bacteria – neutral to alkaline environments Fungi - both neutral and acidic environments

Release of N from the organic matter

• • •

Soil Organic Matter ~5% N 1 to 4% organic N mineralized each year Added organic N sources (C:N ratio < 20 = mineralization

Immobilization z

Immobilization • Conversion of mineral N to organic N by microbes

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Organisms that decompose organic matter as an energy source require nitrogen

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Organic materials with a low N content (C:N > 30) cannot supply the needs of these organisms thus they use soil N in competition with the crop.

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Freshly immobilized N = 5-15% of soil N

Ammonium N Ammonium N = NH4+

• • • • • •

Cation, therefore adsorbed on CEC Won't leach or denitrify Can be fixed in certain clay minerals – micaceous clay Plant uptake Rapidly converted to NO3-N under most conditions Volatilization at high pH NH4+

+

OHHigh pH

→

NH3↑ + H2O Gas

Nitrate N

• Anion, therefore not adsorbed on CEC • Most common mineral form of N in most soils • Most common form taken up by plants • Very susceptible to leaching and denitrification losses

2NO3-

→

N2O & N2

Anaerobic

gases

+

z

No oxygen - wet soil

z

Energy source for bacteria - organic matter

z

Warm temperatures

z

Favored by higher pH

3O2

Phosphorus

http://biology.kenyon.edu/courses/biol112/Biol112WebPage/Syllabus/Topics/Week%2013/PhosphorusCycle.jpg

P Fixation

Factors Affecting P Fixation z

Soil type Andisol>Oxisol≈Ultisol>Inceptisol>Mollisol≈Vertisol Honokaa Waimea Kula

z

z

Kapaa Wahiawa Alaeloa

Makaweli Waialua Keahua Lualualei

Soil pH - acid soils P fixed by Al/Fe oxides - alkaline soils P fixed by Ca Decrease P fixation by liming and/or adding OM

Soil Fertility Depends on: z z

Clay content Clay mineralogy - 2:1 - 1:1 - Oxides

z

Organic Matter

Fertile Soils Infertile Soils z Slightly acid to z Acid to strongly neutral pH acid pH z High CEC z Low CEC z High organic matter z High P fixation Vertisols - Lualualei z Toxicities Mollisols - Waialua Medial Andisols Waimea

Oxisols - Kapaa Ultisols - Haiku Hydrus Andisols - Hilo

Weathering Intensity and Fertility

Smectite

Kaolinite

Oxides

Kauai Category Highly Weathered Very Acid

Series

Classification

Kapaa Halii Makapili Pooku Lawai Mahana Puu Opae Puhi Kalapa kunuweia Hanamaulu Lihue Niu Hihimanu

Very fine, sesquic, isohyperthermic, Anionic Acrudox Fine, ferruginous, isothermic Anionic Acroperox Very fine, sesquic, isohyperthermic, Anionic Acrudox Very fine, ferrihydritic, isohyperthermic, Anionic Acrudox Very fine, ferrihydritic, isohyperthermic, Typic Hapludox Clayey, oxidic, isothermic, Typic Acrohumox Fine, oxidic, isohyperthermic, Ustoxic Palehumult Very fine, ferruginous, isohyperthermic, Humic Kandiustox Very fine, kaolinitic, isohyperthermic, Typic Palehumult Clayey-skeletal, ferritic, isothermic Typic Hapludox Very-fine, ferruginous, isohyperthermic Humic Kandiudox Very-fine, ferruginous, isohyperthermic Rhodic Eutrustox Very fine, kaolinitic, isohyperthermic, Rhodic Eustrustox Very fine, parasesquic, isohyperthermic, Oxic Dystrudepts

Makaweli Pakala Pohakupu Koloa kaloko Kolokolo Mokuleia Mamala Kekaha Iao Waikomo Nonopahu Hanalei Kalihi Nohili Kaena Lualualei Waiawa

Fine, parasesquic, isohyperthermic, Torroxic Haplustolls Fine loamy, parasesquic, isohyperthermic, Torroxic Haplustolls Fine, parasesquic, isohyperthermic, Torroxic Haplustolls Fine, mixed, isohyperthermic, Andic Haplustolls Fine, smectitic, calcareous, isohyperthermic Cumulic Endoaquolls Fine, mixed, isohyperthermic, Cumulic haplustolls Clayey over sandy sandy skeletal, mixed isohyperthermic, Entic Haplustolls Clay, parasesquic, isohyperthermic, Lithic Haplocambids Very-fine, parasesquic, isohyperthermic, Typic Haplocambids Fine, mixed, active, isohyperthermic Cumulic Haplustolls Clayey, mixed, isohyperthermic, Lithic Haplustolls Fine, mixed, isohyperthermic, Chromic Haplotorrerts Very fine, mixed, isohyperthermic, Typic Endoaquepts Fine, halloysitic, isohyperthermic, Fluvaquentic Endoaquolls Very-fine, smectitic, isohyperthermic, Cumulic Haplaquolls Very-fine, smectitic, isohyperthermic, Typic Natraquerts Fine, smectitic, isohyperthermic, Typic Chromustert Clayey smectitic, isohyperthermic, Lithic Vertic Ustropepts

Moderately Weathered Slightly acid Limited Weathering Neutral to alkaline

Paia Kahului Lahaina

Kula Hana Kihei

Kaupo

Kalaupapa Kaluakoi

Halawa

Hoolehua

Kaunakakai

Kamalu

Kona Volcano Pahoa

Summary z

z

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Clay mineralogy important determinant of fertility Organic matter fundamental to nutrient availability Soil fertility in Hawaii closely tied to weathering intensity

Resources Books z

Havlin, J.L., S.L. Tisdale, J.D. Beaton, and W.L. Nelson. 2005. Soil Fertility and Fertilizers. Pearson Education, Inc., Upper Saddle River, NJ

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Foth, H. D. and B.G. Ellis. 1997. Soil Fertility. CRC Press, Inc., Boca Raton FL. Brady, N.C. and R.R. Weil. 2004. Elements of the Nature and Properties of Soils. Pearson Education, Inc., Upper Saddle River, NJ

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Web z z

http://www.extension.iastate.edu/pubs/so.htm http://www.montana.edu/wwwpb/pubs/mt4449.html Excellent short course in soil fertility