Chemistry-of-the-Soil-student-files

Unit Overview

• Focus: Basic concepts in soil chemistry and its relevance to soil fertility.

• Key Topics Covered:

  • Basic chemistry concepts: atoms, compounds, ions, and chemical reactions.

  • Essential soil nutrients for plant growth.

  • Nutrient uptake processes, including Cation Exchange Capacity (CEC) and base saturation.

  • Soil pH and effects on nutrient availability.

Learning Objectives

Concepts

• Basic chemistry concepts pertaining to soil chemistry and nutrient uptake processes.

• Principles of cation exchange and its importance in soil fertility.

• Understanding of soil pH and its impact on nutrient availability.

• Overview of plant nutrients, their cycles, and deficiency symptoms.

Skills

• Building foundational knowledge to support practical organic farming skills.

Instructional Methods

• Lectures: 2 sessions (1.5-2 hours each) to discuss soil chemistry and nutrient cycling.

• Demonstrations: 5 suggested demonstrations to enhance learning through visual representation.

• Assessment: Questions to reinforce key concepts, encouraging comprehension and application.

Required Readings

• Gershuny, Grace. Start With the Soil. Key chapters covering basic soil chemistry.

• Brady, Nyle C., and Ray R. Weil. The Nature and Properties of Soils. Selected chapters for theoretical backing.

Lecture 1: Basic Soil Chemistry Concepts & Nutrient Uptake

Basic Chemistry Concepts

1. Atoms and Elements

• Elements: Basic units of matter (e.g., O, Fe).

• Atoms: Smallest part of an element not broken by chemical means.

• Components: Protons (positive), neutrons (neutral), electrons (negative).

2. Compounds and Molecules

• Compounds: Formed when different elements combine (e.g., H2O).

• Bonds: Atoms join by sharing electrons, forming ionic or covalent bonds.

3. Ions

• Formed by imbalances of protons and electrons. Types include cations (positive) and anions (negative).

4. Plant Nutrients

   • Sources: Carbon, hydrogen and oxygen from air and water; essential nutrients from soil (e.g. N, P, K).

Soil Properties

1. Soil Colloids

   • Tiny particles (0.1 to 0.001 µm) that stay suspended in solution; critical for cation exchange.

2. Soil Solution

   • Water carrying dissolved nutrients and colloidal matter essential for plant uptake.

3. Cation Exchange Capacity (CEC)

   • Indicates soil's ability to retain and exchange cations; influenced by clay and organic matter content.

4. Base Saturation

   • The percentage of CEC sites occupied by bases. High saturation indicates higher fertility.

Nutrient Uptake Processes

1. Root Interception

   • Roots grow into nutrient-rich areas, enhancing uptake.

2. Mass Flow

   • Nutrients dissolved in soil water are drawn into roots via transpiration.

3. Diffusion

   • Movement from areas of high concentration to low; significant for nutrients like P and K.

Lecture 2: Plant Nutrient Requirements & Nutrient Cycles

Nutrient Balance

• Plants need a balance of macronutrients and micronutrients for optimal growth.

Macronutrients and Micronutrients

• Macronutrients: N, P, K (needed in large quantities).

• Micronutrients: B, Cu, Fe, Mn, Mo, Zn (required in trace amounts, but critical).

Nitrogen Cycle

• Fixation: Conversion of N2 gas into usable forms by bacteria.

• Ammonification & Nitrification: Process converting organic N to usable forms.

• Denitrification: Loss of N under anaerobic conditions, which can pollute groundwater.

Phosphorus Cycle

• Necessary for DNA and energy transfer, usually bound tightly to soil particles, making losses minimal except through erosion.

Potassium Cycle

• Vital for photosynthesis and growth, mobile in soil, but may be trapped in clay particles; sources include wood ash and granite dust.

Micronutrient Function

• Iron: Important for chlorophyll synthesis, deficiency causes yellowing.

• Manganese: Important for metabolism and photosynthesis; symptoms include grey specks.

• Zinc: Key for enzyme activation, symptoms include stunted growth and mottled leaves.

Sources of Nutrients

• Recycled organic matter, various amendments, and careful management of soil to maintain nutrient levels.