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42. Root Zone Soil Water

This chapter focuses on the root zone soil water, emphasizing its significance in various agricultural and hydrological applications. Key concepts include the types of soil water, soil moisture constants, and the dynamics involved in plant-water interactions. Methods for estimating root zone moisture and essential practices for irrigation scheduling and water resource management are also discussed.

Sections

Root Zone Soil Water

This section explores the role and dynamics of water in the root zone, including types of soil water, moisture constants, water movement, and estimation methods for effective agricultural practices.

42 Section Overview

Start current section content and materials

42.1 Soil Water in the Unsaturated Zone

The unsaturated zone, or vadose zone, is crucial for plant water absorption, containing gravitational, capillary, and hygroscopic water, each with varying availability to plants.

42.1.1 Types of Soil Water

Soil water is categorized into three types based on its availability to plants: gravitational water, capillary water, and hygroscopic water.

42.2 Field Capacity and Wilting Point

Field Capacity and Wilting Point are critical soil moisture constants that define the range of water availability for plant growth.

42.3 Rooting Depth and Root Zone Storage Capacity

This section discusses the concepts of rooting depth and root zone storage capacity, highlighting their significance in water absorption by plants and water management in agriculture.

42.3.1 Rooting Depth

Rooting depth indicates how deep plant roots typically grow and affect water absorption.

42.3.2 Root Zone Storage Capacity (RZSC)

The Root Zone Storage Capacity (RZSC) indicates the total amount of water stored between field capacity and wilting point in the soil that is accessible to plant roots.

42.4 Soil-Water Characteristic Curve (SWCC)

The Soil-Water Characteristic Curve (SWCC) illustrates the relationship between soil moisture and matric potential, crucial for water movement modeling and irrigation scheduling.

42.5 Infiltration and Redistribution in the Root Zone

Infiltration is the process by which water enters the soil and redistributes within the root zone, affecting water availability and soil moisture dynamics.

42.5.1 Infiltration

Infiltration is the process by which water enters the soil surface and begins to move downward, significantly influencing water availability in the root zone.

42.5.2 Redistribution

Redistribution in the root zone pertains to how water moves within the soil after infiltration, affecting water availability and plant uptake.

42.6 Plant-Water Interaction and Uptake

Plants extract water through their roots using gradients in water potential, which are influenced by root density, soil moisture levels, and evaporative demand.

42.7 Evapotranspiration from the Root Zone

Evapotranspiration (ET) encompasses the processes of evaporation from soil and plant surfaces, as well as transpiration through plant stomata, and is crucial for managing soil moisture within root zones.

42.7.1 Types of ET Estimates

This section discusses the two primary types of evapotranspiration (ET) estimates: potential ET and actual ET.

42.8 Moisture Movement in Unsaturated Soil

This section explores the principles governing water movement in unsaturated soil, focusing on Darcy’s Law for unsaturated flow and factors affecting hydraulic conductivity.

42.9 Methods to Estimate Root Zone Soil Moisture

This section discusses various methods to estimate root zone soil moisture, exploring both direct and indirect techniques used in practice.

42.9.1 Gravimetric Method

The gravimetric method involves measuring soil moisture by weighing soil samples before and after drying, providing a highly accurate yet time-consuming assessment.

42.9.2 Neutron Scattering

Neutron scattering is a non-destructive method used to estimate root zone soil moisture by measuring hydrogen atoms in the soil.

42.9.3 Time Domain Reflectometry (TDR)

This section discusses Time Domain Reflectometry (TDR), focusing on its methodology for estimating soil moisture content effectively.

42.9.4 Remote Sensing & Satellite-Based Estimation

This section discusses the role of remote sensing and satellite technologies in estimating root zone soil moisture.

42.10 Irrigation Scheduling Based on Root Zone Water Balance

This section discusses the water balance approach to irrigation scheduling, focusing on the management of soil moisture for optimal plant growth.

42.11 Modeling Root Zone Water Dynamics

This section discusses the common models used to simulate root zone water dynamics, focusing on soil moisture, evapotranspiration, root uptake, and percolation.

42.12 Factors Affecting Root Zone Water Availability

This section discusses the various factors influencing water availability in the root zone, crucial for plant growth.

42.13 Engineering Applications and Importance

This section discusses the significance of understanding root zone water for various engineering applications.

Learning Objectives

  • The root zone is crucial for plant water absorption and hydrology.

  • Soil water is classified into gravitational, capillary, and hygroscopic types.

  • Field capacity and wilting point help determine available water for plants.

Key Concepts

Field Capacity (FC)

The maximum amount of soil moisture remaining after excess water has drained away.

Permanent Wilting Point (PWP)

The soil moisture level at which plants can no longer extract water.

Root Zone Storage Capacity (RZSC)

The total volume of water that can be stored within the root zone between field capacity and permanent wilting point.

Evapotranspiration (ET)

The combined process of evaporation from the soil and transpiration through plant stomata.

Practice Exercises

Total Questions

2

Estimated Time

4 min

Passing Score

70%

Instructions

  • Read each question carefully
  • You can use hints if you need help
  • Complete all questions before submitting
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