Fundamentals of Nutrient Management...Nature and Properties of Soils, Brady and Weil similar diagram on p. 67 of the MANMH Department of Environmental Science and Technology Why Liming

Department of Environmental Science and Technology

Soil Fertility

Fundamentals of Nutrient ManagementJune 1, 2010

Patricia SteinhilberDepartment of Environmental Science and Technology

Ag Nutrient Management Program

University of Maryland College Park


Main Topics

• plant nutrition

• functional soil model

• soil chemical properties relating to soil fertility


Plant Nutrition Topics…

• growth factors

• plant nutrients

• mechanisms for nutrient delivery

• law of minimum


Growth Factors:What do plants need to grow?

1. water2. oxygen3. heat4. carbon dioxide5. mechanical support6. nutrients


Definition of a Nutrient• an element that has a direct effect on

growth or metabolism

• required by plants to complete their vegetative and reproductive stages of life

• must be specifically required and can not be replaceable by another element


Non-mineralNutrients

Mineral Nutrients

carbonoxygenhydrogen

macronutrients micronutrients

primary secondary iron cobalt nickelzinc chlorineManganese boroncopperMolybdenum

nitrogenphosphoruspotassium

calciummagnesiumsulfur

What elements do plants require?(Table 4-2, p. 56, MANMH)


Forms in Which Nutrients Exist

• cation – positively charged ion

• anion – negatively charged ion

• neutral – uncharged


So which nutrients exist in what form?

(Table 4-1, p. 55, MANMH)

• ammonium – NH4+

• potassium – K+

• calcium – Ca+2

• magnesium – Mg+2

• iron – Fe+2, Fe+3

• zinc – Zn+2

• manganese – Mn+2, Mn+4

• copper – Cu+2

• cobalt – Co+2

• nickel – Ni+2

• nitrate – NO3-

• phosphate – H2PO4- ,

HPO4-2

• sulfate – SO4-2

• chlorine – Cl-

• borate – H3BO3, H2BO3-,

B4O7-2

• molybdate – MoO4-2


Plant Nutrient Terminology

• mineral nutrients• non-mineral nutrients• macronutrients• primary nutrients• secondary nutrients• micronutrients


Relationship between Plant Growth and Nutrient Concentration

• What happens when a nutrient or nutrients are inadequate in supply?

• Can the concentration of a nutrient be too high?

• The next diagram addresses these questions.



How can you tell if a nutrient is deficient?

• visual symptoms– note location and type

OMAFRA


How can you tell if a nutrient is deficient?

• visual symptoms– note location and type– http://www.mawaterquality.org/publications/pubs/manmh/chapter4.ppt

– deficiency is severe if noticeable• diagnostics via plant analysis

– sample correct plant part at the correct time– see Soil Fertility Guide, PL-1, Plant Tissue

Analysis


hidden hunger


What happens when more than one nutrient is

inadequate?


Liebig-Sprengel Law of the Minimum

• Growth is limited by the growth factor present in the least adequate amount.

• Yield is proportional to most limiting factor.

• Barrel stave example is the most common representation.



Penn State Agronomy Guide


Mechanisms for Nutrient Delivery

• mass flow– the passive movement of nutrients in soil water to

roots

• diffusion – the movement of nutrient from regions of high

concentration to regions of low concentration

• root interception– direct contact of nutrients with roots as roots grow and

explore soil


Important Mechanisms of Delivery


Practice Question #1

Examples of macronutrients are the following:

A) nitrogen, iron and potassium;B) phosphorus, nitrogen and calcium;C) sulfur, nitrogen and zinc;D) potassium, magnesium and cobalt.


Functional Soil Model

• beyond the pie chart

• expand our vocabulary & concepts

• 2-D slice of a soil


A

B

C

D

E

F

G


soil solution

soil air

primaryminerals

secondaryminerals

residuesandby-products

humus

biomass

inorganicsolids

organicsolids

pore space


Surface Area and Reactivity



Soil Chemistry and Soil Fertility

• pH

• soil clays and reactive surfaces

• managing soil pH


What is pH?

• “p”

• H


What is pH?

• “p” – negative log– a mechanism to make communication about

very small numbers (decimal fractions) easier• “H” – hydrogen ion concentration (activity)

– [H+] or (H+)

pH = -log [H]


Some pH Facts• pH and hydrogen ion concentration are

inversely related.• As pH increases, hydrogen ion

concentration decreases.• descriptors

– acid (pH<7)– basic or alkaline (pH>7)– neutral (pH=7)


[H+] - pH relationship[H+] (moles/L) [H+] (moles/L) pH

.1 10-1 1

.01 10-2 2

.001 10-3 3

.0001 10-4 4

.00001 10-5 5

.000001 10-6 6

.0000001 10-7 7

.00000001 10-8 8

.000000001 10-9 9


pH of Soils and Other Materials


Practice Question #2

If the hydrogen ion concentration of a soil is 0.0000001, its pH is

a) 4b) 5c) 6d) 7


Cation Exchange Capacity(CEC)

• ability of a soil to hold cations on charged sites

• measure of the net negative charge of a soil

• expressed as meq/100g (old) or cmole/kg (new)


Importance and Consequences of CEC

• Exchange phase is the storehouse of cationic nutrients.

• Exchangeable cations are protected from leaching.

• Dynamic equilibria exist between nutrients in the soil solution and on exchange sites.



Mechanisms/Types of Charge Development

• isomorphic substitution (permanent charge)– main mechanism for clay minerals

• protonation and deprotonation of surfaces (variable or pH-dependent charge)– gain or loss of a H+ at a surface– main mechanisms for hydrous oxides and organic

matter– occurs broken edges of clay minerals


Building Blocks of Aluminosilicate Clays




Aluminosilicate Clay Minerals

Name Structure Layers CEC

kaolinite 1:1 3-15

montmorillonite 2:1 80-120

illite (hydrous mica)

2:1 15- 40

vermiculite 2:1 120 -150

chlorite 2:1:1 15- 40




Variable (pH-dependent) Charged Sites

• hydrous oxides of iron, aluminum and manganese,

• humus, and

• edges of aluminosilicate clays.


How does pH-dependent charge arise?


On a Humus Molecule…


Cation Exchange Capacities of the Common Soil Colloids

Soil Colloid Cation Exchange Capacity(cmolc/kg of colloid)

humus 100-300

vermiculite 120-150

montmorillonite 60-120

illite 15-40

iron oxides 0-3*

*at pH 7


Soil Texture and Cation Exchange Capacity

Soil Texture Cation Exchange Capacity(cmolc/kg)

sands 1-5

fine sandy loams 5-10

loams and silt loams 5-15

clay loams 15-30

clays >30


Factors Affecting CEC of Soils

• amount of clay-sized particles (texture)

• kind of clay

• amount of humus

• pH


Just how much does a change in pH affect CEC?

Pratt & Bair,1962


Base Saturation• percentage of the exchange capacity

occupied by basic cations– calcium (Ca), magnesium (Mg), potassium

(K), sodium (Na)• hydrogen (H) and aluminum (Al) are acidic

cations• greater base saturation, the more fertile

the soil


Base Saturation• routine analysis by some soil testing labs• Example: exchangeable cations were

extracted and measured (cmoles per 100 grams soil)H – 3Ca – 12Mg – 5Na – 1K – 4

What is the CEC of this soil?

What is the base saturation (%)?


Types of Soil Acidity

• active acidity• reserve acidity


Where/How does soil acidity originate?

• nitrification (oxidation) of ammonium– most fertilizers and all organic sources– 2 H+ per 1 NH4

+1

• organic acids produced by plant roots and microbes

• rainfall – carbonic acid, nitric acid, sulfuric acid

• hydrolysis of aluminum – 3 H+ per 1 Al+3

• oxidation of sulfur– 2 H+ per 1 S


Nature and Propertiesof Soils, Brady and Weil

similar diagram on p. 67 of the MANMH


Why Liming to Reduce Soil Acidity is Helpful…


Many crops prefer a specific pH range for optimal growth.


Target pH in Maryland• pH 7.0

– alfalfa establishment• pH 5.6

– tobacco• pH 5.2

– potatoes, sweet potatoes• pH 6.5

– most other agronomic and horticultural crops


Adjusting Soil pH

• Lime materials are used to neutralize acidity and raise pH.

• Acid-forming materials are used to produce acidity and decrease pH. – elemental sulfur, iron sulfate, aluminum

sulfate


Is lime required?

• Depends upon

– crop and its optimal pH range

– pH of the soil solution (active acidity)


How much lime is required?• Depends upon

– target pH– pH of soil solution– reserve acidity

• “lime requirement” (LR) is a process or chemical test which estimates the amount of pure, fine limestone needed


Soil Tests for LR:Soil-Buffer Equilibrations

• mix soil and a carefully-designed buffer solution

• equilibrate (15 – 30 min.)• measure pH of soil-buffer mixture• the more the soil lowered the pH of the

buffer mixture, the greater the lime requirement


Popular Buffers

• SMP buffer (pH 7.0)– named for Shoemaker, McLean and Pratt– developed in mid-West for soils with high LR

• high organic matter content and medium to fine textures, 2:1 clays

• Adams-Evans buffer (pH 8.0)– developed in southern U.S. for soils with low

CEC and small amounts of 2:1 clays and OM• Mehlich buffer (pH 6.6)

– developed in North Carolina


From Adams-Evans Buffer to LR(target pH = 6.5, pounds of limestone)

pH buffer

pH H2O 7.8 7.6 7.4 7.3

6.3 366 732 1098 1281

6.1 648 1295 1943 2267

5.9 872 1744 2616 3052

5.7 1056 2112 3169 3697

4.7 1672 3343 5015 5850


Texture and Lime Requirement


How often is lime required?

Brady & Weil, 13th edition


When should lime be applied?

• 2-6 months before most sensitive crop

• data from Alley at VPI indicate that application at planting improved yield

lime rate(tons/A)

alfalfa yield(pounds/A)

0 303

1 1,229

3 1,817

6 2,262


Review Question #3

Cation exchange is affected by a) amount of clayb) type of clayc) amount of humusd) pHe) all of the above


Questions?

Lemke, UWSP

Documents

Fundamentals of Nutrient Management...Nature and Properties of Soils, Brady and Weil similar diagram on p. 67 of the MANMH Department of Environmental Science and Technology Why Liming