SOS206D_Unit 2_2024

Table of Contents

• Chapter 1: Introduction

• Chapter 2: Soil Water Content

• Chapter 3: Scheduling Irrigation

  • 3.1 Upper and Lower Limit of Plant Available Water

  • 3.2 Crop Water Use

  • 3.3 Irrigation Scheduling Using Class-A Pan Evaporation, Crop Factor and the Book Keeping Method

• Chapter 4: Infiltration Rate

  • 4.1 Definitions

  • 4.2 Measurement

  • 4.3 Practical Example

  • 4.4 Factors Affecting Infiltration Rate of Soil

• Chapter 5: Irrigation Methods

  • 5.1 Surface Irrigation

  • 5.2 Overhead Irrigation

  • 5.3 Micro Irrigation

  • 5.4 Subsurface Irrigation

• Assessment Criteria

• Bibliography

• Appendix: Application of the Book Keeping Method in Irrigation Scheduling

Soil Water and Irrigation

1. Introduction

   • Soil stores water for plant growth, essential for processes like photosynthesis, solvent for biochemical reactions, and maintaining turgor pressure.

   • 99% of absorbed water is evaporated through transpiration.

2. Soil Water Content

   • Crucial for determining water stored in soil.

   • Expressed on mass (gravimetric) and volumetric basis.

     • Gravimetric soil water content (Өm): mass of water per unit mass of dry soil.

     • Volumetric water content (Өv): volume of water per unit volume of soil.

   • Measurement methods outlined, including lab techniques and equations for calculating water content and root zone depth.

Scheduling Irrigation

1. Key Concepts

   • Full irrigation aims to maintain soil water content between upper (field capacity) and lower (permanent wilting point) limits.

   • Maximum plant-available water content calculated from the difference between field capacity and permanent wilting point (PAW = FC - PWP).

   • Irrigation is scheduled before depletion reaches the permanent wilting point.

2. Crop Water Use

   • Refers to water lost via evapotranspiration.

   • Depends on weather and crop characteristics; methods include Class-A pan evaporation and crop factors to estimate needs.

Infiltration Rate

1. Definition

   • Infiltration: process of water entering soil; varies by type, soil conditions, and is measured using double ring infiltrometers.

2. Factors Affecting Infiltration

   • Influenced by soil texture, water content, and soil structure. Coarse soils have higher rates than fine textured soils.

Irrigation Methods

1. Overview of Methods

   • Surface Irrigation: simple, gravity-fed; suited for level land. Techniques include basin, border strip, and furrow irrigation.

   • Overhead Irrigation: simulates rain, can be used on variable terrains but faces evaporation losses and uneven distribution in wind.

   • Micro Irrigation: efficient, uses small devices to apply water; complex and best for high-value crops.

   • Subsurface Irrigation: waters roots directly below surface, high efficiency but posed clogging risks.

Appendix: Book Keeping Method of Irrigation Scheduling

• Utilizes Class-A pan data to track soil water and plan irrigations. Includes example calculations for a tomato crop, emphasizing the importance of accurate measurements for effective irrigation management.