Soils and Plant NutritionMaster Gardener Class

Soil is the medium in which plants grow - the basis for plant growth.

I can’t get any respect. People treat me like dirt!

What is Soil?

Mineral45-48%

Air

20-30%

Water

20-30%

Organic Matter

2-5%

• Sand

• Silt

• Clay

Four Major Components of Soil

Soil Components

Mineral

Sand = 2.0 to 0.05mm

Silt = 0.05 to 0.002mm

Clay = less than 0.002mm

The proportion of sand, silt and clay determine a soil’s texture.

Soil texture Soil texture determines adetermines asoil’s water-soil’s water-

holding holding capacitycapacity

Relationship Between Soil Textureand Water Availability

• Improves the soil’s physical condition.

• Supplies plant nutrients.

• Increases water infiltration.

• Helps decrease erosion.

• Improves soil tilth (the soil’s ability to resist compaction).

••• Basically nature’s way of recycling!

Five Things Organic Matter Does for Soil:

The Ideal Soilfor Crop Production

• Medium texture and organic matter for air and water movement

• Sufficient clay to hold soil moisture reserves

• Deep, permeable subsoil with adequate fertility levels

• Environment for roots to go deep for moisture and nutrients

1 352 603 754 855 956 100

Soil Depth InfluencesRelative Productivity

Soil depth usable Relativeby roots, ft. productivity, %

Soil depth usable Relativeby roots, ft. productivity, %

Soil slope, % Not easily eroded Easily

eroded

Soil slope, % Not easily eroded Easily

eroded

Soil Slope AffectsRelative Productivity

0-1 100 951-3 90 753-5 80 505-8 60 30

Relative productivity, %

The smallest particles of soil are called colloids. Colloids have a negative charge so they attract

positively charged particles. Colloids repel other negatively charged particles - like a magnet.

An element or group of elements with an electrical charge is called an ion.

Ions with negative charges are called anions. Ions with positive charges are

called cations.

Unlike a magnet, colloids can only hold a limited number of cations. The total amount of exchangeable cations a soil can hold (the amount of its negative charge) is called its Cation Exchange Capacity or CEC.

Soil Colloid

K+

Potassium

H+

Hydrogen

2Ca +

CalciumMg +

2

Magnesium

Cation Exchange Capacity

Plant Nutrients 1616 Nutrient

elements are essential

for plant growth and

reproduction.

Plant Nutrients

C HOPKN’S CaFe Mg B Mn Cu Zn Mo Cl

See Hopkin’s Cafe Managed By My Cousin Mo Clay

Carbon - Hydrogen - Oxygen

The three most abundant elements - plants obtain them from water and

air.

These three elements make up more than 94% of plant dry tissue. The remaining 13 elements make

up less than 6% of plant dry tissue.

Nitrogen

Phosphorus

Potassium

Sulfur

Calcium

Magnesium

Manganese

Iron

Boron

Zinc

Copper

Molybdenum

Chlorine

Macronutrients

Micronutrients

Roots Roots contact onlycontact only

a small a small percentagepercentageof available of available nutrientsnutrients

• A nitrogen deficiency most limits plant growth.

• Provides a visual green response in plants.

• Plants use large amounts of nitrogen.

• Necessary for the production and transfer of energy - photosynthesis.

• Stimulates plant growth.

• Increases seed and fruit yield.

• Improves the quality of leaf and forage crops.

• Present in the soil in three forms.

Nitrogen . . . (N)Nitrogen . . . (N)

Nitrogen is present in the soil in three major forms:

• Organic

• Inorganic

• Elemental

The Nitrogen CycleAtmospheric

nitrogenAtmospheric

fixation and deposition

Animalmanures

and biosolids

Industrial fixation(commercial fertilizers)

Crop harvest

Volatilization

Denitrification

Runoff anderosion

Leaching

Organicnitrogen

Ammonium(NH4)

Nitrate(NO3)

Plant residues

Biologicalfixation by

legume plants Plantuptake

Immobilization

Immobilization

Mineralization

Mineralization

Input to soil ComponentLoss from soil

-+

Nitrogen Deficiency

Phosphorus . . . (P)Phosphorus . . . (P)

• Also an essential part of photosynthesis.

• Responsible for utilization of starch and sugar.

• Cell nucleus formation.

• Cell division and multiplication.

• Cell organization.

• Transfer of heredity.

Phosphorus Cycle

Phosphorus Deficiency

Potassium . . . (K)Potassium . . . (K)

• After nitrogen, plants use the largest amount of potassium.

• Plays an essential role in the metabolic process of plants.

• Plays a role in raising the disease resistance of many plant species.

How Potassium Moves in Soil

Potassium Deficiency

Calcium . . . (Ca)Calcium . . . (Ca)

• An essential part of the wall structure and strength of plant cells.

• Provides for normal transport and retention of other elements.

• Does not move in plant, deficiency develops in new leaves

• Counteracts the effects of alkali salts and organic acids within the plant.

Magnesium . . . (Mg)Magnesium . . . (Mg)

• Is essential for photosynthesis.

• Makes up a part of the chlorophyll in green plants.

• Helps activate plant enzymes needed for plant growth.

• Dolomitic lime and epsom salts contain Magnesium

Magnesium Deficiency

Sulfur . . . (S)Sulfur . . . (S)

• Activates plant enzymes.

• Is required for nodulation and nitrogen fixation of legumes.

• Present in glycosides which give the characteristic odors and flavors of mustard, onion and garlic.

Soil organic

matter is a

major

source of SSS

Manganese . . . (Mn)Manganese . . . (Mn)

• Activates plant enzymes.

• May substitute for magnesium

Iron . . . (Fe)Iron . . . (Fe)

• Essential for the synthesis of chlorophyll.

• Symptoms include chlorosis between the veins with green veins

Copper . . . (Cu)Copper . . . (Cu)

• Essential for plant growth.

• Activates many plant enzymes.

Zinc . . . (Zn)Zinc . . . (Zn)

• Regulates plant growth by controlling the synthesis of indoleacetic acid.

• Activates plant enzymes.

Boron . . . (B)Boron . . . (B)

• Regulates the metabolism of carbohydrates in plants.

Molybdenum . . . (Mo)Molybdenum . . . (Mo)

• Required in tiny amounts.

MicronutrientsMicronutrientsARE NOTARE NOT

miracle workersmiracle workers

Nutrient Deficiencies

A note about nutrient deficiencies:

While many deficiencies show specific symptoms this is an inexact science at best.

Many of the symptoms overlap so the only way to be sure is with a combination of tissue analysis and soil sampling.

Nutrient Deficiency Symptoms

Nutrient

Position on plant Chlorosis

Leaf margin necrosis?

Color and leaf shape

N All leaves Yes No Yellowing of leaves and leaf veins

P Older leaves

No No Purplish patches

K Older leaves

Yes Yes Yellow patches

Mg Older leaves

Yes No Yellow patches

Ca Young leaves

Yes No Yellow leaves

S Young leaves

Yes No Yellow leaves

Mn, Fe Young leaves

Yes No Interveinal chlorosis

B, Zn, Cu, Mo

Young leaves

- - Deformed leaves

Soil pH is a measure of the hydrogen ion

concentration in the soil.

Buffer pH is the soil’s ability to resist changes

in pH.

Optimum pH for most plants

5.5 to 6.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neutral

Range of AlkalinityRange of Acidity

pH Units

Ideal

Factors in Addition to Soil pH Which Influence the Frequency of Liming

• Soil texture• Rate of N fertilization• Rate of crop removal of Ca and Mg• Amount of lime applied• pH range desired• Tillage system• Irrigated crops

Why Acid Soils Should Be Limed

• Increases CEC in variable charge soils

• Increases availability of several nutrients

• Supplies Ca and Mg to plants

• Improves symbiotic N fixation in legumes

• Improve crop yields

• Reduces Al and other metal toxicities

• Improves the physical condition of the soil

• Stimulates microbial activity in the soil

Soil Acidity Affects Plant Growth

• Aluminum, Fe and Mn can reach toxic levels because of increased solubilities in acid soils

• Reduced activity of organisms responsible for the breakdown (mineralization) of organic matter

• Possible Ca deficiency . . . but most likely a Mg deficiency

Soil Acidity Affects Plant Growth

• The performance of soil-applied herbicides can be adversely affected

• Reduced activity of symbiotic N fixing bacteria

• Clay soils high in acidity are less highly aggregated

• Availability of nutrients such as P, K and Mo is reduced

• Tendency for K to leach is increased

How Lime Reduces Soil Acidity

• Ca2+ ions from aglime replace Al3+ at the exchange sites. The Al3+ reacts with water releasing H+…

• Carbonate ions (CO32-) from aglime react in the soil solution,

creating excess OH- (hydroxyl) ions which combine with H+ ions forming water

• The pH increases because the acidity source (H+) has been reduced

(Al3+ + H2O Al(OH2+) + H+

Liming Materials

• Calcitic Lime

• Dolomitic Lime

• Hydrated Lime(Use 75% of the above recommended amount)

• Wood Ashes(Use with caution!)

Relative Neutralizing Values of Some Common Liming

Materials

RelativeLimingneutralizingmaterial value, %

Calcium carbonate

100Dolomitic lime

95-108Calcitic lime

85-100Baked oyster shells

80-90Marl

50-90Burned lime

150-175

Burned oyster shells

90-110Hydrated lime

120-135Basic slag

50-70Wood ashes

40-80Gypsum

NoneBy-products

Variable

RelativeLimingneutralizingmaterial value*, %

*Relative neutralizing value is used interchangeably here with calcium carbonate equivalent

Particle SizeDetermines Lime Reactivity

0

20

40

60

80

100

4-8 8-20 20-50 50-100

Lim

e re

acte

din

1 t

o 3

year

s, %

Finer particle size(logarithmic scale of mesh size)

For best results, apply lime well ahead of planting to allow

sufficient time to neutralize soil acidity

Fertilizer ratio describes the

relative proportions of N-P-K in a fertilizer.

Fertilizer grade (or analysis) refers to how much of an element there is in a fertilizer based on percentage

by weight.

• Complete when it contains all three major plant nutrients.

• Incomplete when it lacks one of the major plant nutrients.

• Balanced when it contains equal amounts of N-P-K.

• Premium refers to fertilizers that contain the minor elements

• Slow release refers to fertilizers that release the elements slowly over time

Fertilizer is referred to as:

Let’s Do Some MATH

• Many fertilizer recommendation come as pounds of (insert element) per 1000 square feet.

• If you add that much product you will NOT get the right amount because the product contains only a percentage of the element.

• So now what do you do?

To determine the amount of ammonium sulfate a 5,000-sq ft lawn needs if the lawn requires one lb of nitrogen per 1,000 sq

ft...Lawn: 5,000 sq. ft.

Fertilizer: Ammonium sulfate (21-0-0)

Rate of Application: 1lb of nitrogen per 1,000 sq. ft.

• Ammonium sulfate is 21% nitrogen.

• 21% is the same as 0.21 or 21/100.

• This means for every 100 lb. of fertilizer there are 21 lb. of nitrogen.

• We need 1 lb of nitrogen for every 1,000 sq. ft. Using proportions, we can calculate the amount of ammonium sulfate needed to get 1 lb of N. “X” represents the unknown amount being calculated.

21 lb. N

100 lb. 21-0-0

=

=

1 lb. N

X lb. 21-0-0

Tim’s Method

• ½ lb/1000 ft2 = 50

• 1 lb/1000 ft2 = 100

• 1.5 lb/1000 ft2 = 150

• 2 lb/1000 ft2 = 200

• 2.5 lb/1000 ft2 = 250

See the pattern?

To get the right amount of product take the constant supplied on the right and divide by the analysis of the element you want.

For the example to apply 1 lb of nitrogen /1000 ft2 using 21-0-0. 100/21 = 4.76 lbs of 21-0-0 per 1000 ft2.

How much lime and fertilizer

should I add to my garden?

Soil testing is essential to applying the correct fertilizer and Lime!

Adding fertilizer to the soil without testing is like baking a cake without reading the recipe or measuring the ingredients

The greatest The greatest potentialpotential

for error in soil for error in soil testingtesting

is in taking the is in taking the samplesample

A good sample is critical to

getting a good soil analysis!

Sampling for Home Gardens and Lawns

• Consider different soils and management situations that need to be sampled

Plant analysis and soil testing go hand-

in-hand

Soil Testing vs. Plant Analysis• Soil testing and plant analysis are

complementary, but very different …– Soil tests predict nutrient availability– Plant analysis assesses nutrient uptake

• Soil tests are not always good predictors of nutrients that leach easily, i.e. N or S

• Plant analysis is a better tool to assess some micronutrients, e.g. B, Fe, Mo

Let’s Review

• To a horticulturist what is soil?

• What is organic matter and what does it do for the soil?

• What is pH? What is buffer pH?

• How can I KNOW how much lime and fertilizer to add?

Other Recommended Information

Follow the Links• Home and Garden Infor

mation Center (HGIC)• Soil testing• Changing the pH of you

r soil• Fertilizers• Composting

• Bob Lippert’s Soil Page• Indoor plants• Fertilizing Lawns

• Mulch

• Fertilizing Trees

• Fertilizing Vegetables

• www.clemson.edu/sandhill

• On the left you will see a link to the South Carolina Master Gardener Program.

• This program is available under both powerpoint presentations and Electronic Training

Credits

I am not a soil scientist so much of this was taken from several sources. Some of the following are sources I’ve “stolen” this information from. Thanks to all who

had a part.

•South Carolina Master Gardener Manual

•Home and Garden Information Center (http://hgic.clemson.edu)

•Bob Lippert’s Powerpoint (Clemson University) Slide Presentation

•Michelle Clark’s (Richland County Master Gardener) MG Slide Presentation

•Brian Smith’s (Charleston County Extension Agent) COTS Slide Presentation

This concludes our lesson.

If you have questions feel free to email me at rdncn@clemson.edu