CHEMICAL AND BIOLOGICAL

PROPERTIES OF THE SOIL

KARAN VERMA COA, PALAMPURCSKHPKV PH.D

AGRONOMY

Lesson Objectives

Describe the properties of acids and bases. Differentiate between strong and weak

acids, strong bases and weak bases. Use the pH scale to calculate and measure

the concentration of oH. Relate soil pH to nutrient availability.

Lesson Objectives continued

Investigate the effect of soil pH on plant growth.

Develop a plan for changing soil pH to meet crop needs.

Determine how to take a soil sample for testing.

What is the pH scale? The pH scale

measures how a c id ic or ba s ic a solution is.

The pH scale

The pH scale is the concentration of hydrogen ions in a given substance.

[ ]+−= HpH log

Identifying Acids and Bases

Acids have a ph from 0-7 Lower pH value indicates a

stronger acid.

Ba s e s have a pH from 7-14 Higher pH value indicates a

stronger base.

Definitions of Acids and Bases

An acid is a substance that breaks into ions in an aqueous solution.

A Base (alkaline) is a substance that breaks into ions in an aqueous solution.

Note: aqueous solution is any solution where is the solvent.

[ ]+H

[ ]−OH

[ ]−OH

OH 2

Did we Miss something??

What happens when the pH of a substance is 7?

Ans: A pH level of 7 indicates a Neutral Substance i.e: Water!

Test Your Knowledge

What is the range of an ACID on the pH scale?

Ans: 0-7

What is the range of a BASE and what is another name for a BASE?

Ans: 7-14, Alkaline

Characteristics Of Acids

Acids can be characterized by:

1. A sour taste.

2. It turns blue litmus paper red

3. It tastes sour. Try drinking lemon juice (citric acid)

Characteristics of Bases

A Base is characterized by:

1. A bitter taste. (Milk of Magnesia)

2. It feels slippery. (Soapy Water)

3. It turns Red Litmus Blue.

pH Scale

Each pH point multiplies acidity by a factor of 10.

A pH of 5.0 is 10 times more acid than pH 6.0 and 100 times more acid than pH 7.0.

Why Learn about Acids & Bases?

What do you think is the pH level of (Your Town) tap water?

The pH of a swimming pool must be checked periodically. Why?

Is it important for Lakes & Rivers to maintain a certain pH?

How to calculate concentration of OH-?

OH-= 14 - pH

Soil pH requirementsBeans 6.0-7.0

Broccoli 6.0-7.0

Cabbage 5.6-6.6

Cantaloupe 6.0-7.0

Cauliflower 6.0-7.0

Cucumber 5.0-6.0

Eggplant 5.0-6.0

Garlic 5.0-6.0

Okra 6.0-8.0

Peanuts 5.0-6.0

Symptoms of nutrient deficiencies

Deficiency- plant condition where an essential nutrient is not sufficiently available.

Symptom- a visual sign or condition that results from a deficiency

Primary nutrient deficiency symptoms

Nitrogen (N)- Stunted and spindly- yellow, yellowish green or light green in leaf

color (chlorosis)- Older leaves affected first, starting at the tip

and moves along the middle of the leaf

Phosphorus (P)- stunted growth- Very dark green color- Purple leaves or portions of leaves in

advanced stages- Older leaves affected first

Primary nutrient deficiency symptoms

Potassium (K)- Shorter plants- Bronzing or browning of leaf color- Lodging (bending of stem) occurs

Primary nutrient deficiency symptoms

Sulfur (S)- Young plants have stunted appearance- Leaves have light-green to yellow coloring- Stems are thin and spindly- Sulfur deficiency symptoms are similar in

appearance to Nitrogen deficiency symptoms

Secondary nutrient deficiency symptoms

Magnesium (Mg)- Leaf parts between veins show a whitish color- Leaf tissue becomes yellow, veins remain

green- Leaves curl upward along the margins

Secondary nutrient deficiency symptoms

Macronutrients

Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur

Micronutrients

Boron Copper Iron Chloride Manganese Molybdenum Zinc

pH

Determines the solubility and availability of nutrients

General range for most cases: 6.5 to 7

Biological Effects on pH

More organic matter (decaying plant matter and animal debris) lowers soil pH

More organic matter can support larger number of microorganisms

Microorganisms release Nitrogen into the soil and make N more available

Effect of pHon nutrient availability

Cation Exchange Capacity

soil’s ability to exchange and retain cations cation- positively charged ion anion- negatively charged ion

A high CEC soil will be able to resist changes in pH

Macronutrients

Most macronutrients are more available within a pH range of 6.5 to 8.

the exception to this is P, which likes the pH to be from 6 to 7.

Ca, K, and Mg are prone to leaching at a low pH.

Plant uptake of N and P is restricted at pH below 6.

Micronutrients Most micronutrients (B, Cu, Fe, Mn, Ni, and

Zn) are more available within a pH range of 5 to 7

Metals (Cu, Fe, Mn, Ni, and Zn) and bound tighter to the soil at high pH. Low pHs can cause toxicities.

Micronutrients decrease in availability as pH approaches 8.

Chlorine is rarely deficient at high pH levels, but can become toxic as pH increases.

Steps for Soil Sampling

Steps for Soil Sampling

Steps for Soil Sampling

Steps for Soil Sampling

Steps for Soil Sampling

Steps for Soil Sampling