Soil Moisture

Introduction

Soil moisture is water that is held in the air pockets, or pore spaces, between soil particles. Soils collect, store, and release water. Collection occurs as water enters the soil through surface pores such as during a rain storm. Water is stored in the pore spaces until it is taken up by the roots of a plant, or it evaporates from the soil surface, or it is pulled deeper into the ground by gravitational forces.

Dry soil is made up of minerals and pore spaces. A typical volumetric ratio would be 55% minerals and 45% pore space. As water is added to the soil, the pore spaces begin to fill with water. Soil that seems damp to the touch might now have 55% minerals, 35% pore space and 10% water. This would be an example of 10% volumetric water content. The maximum water content for this soil is 45% because at that value, all the available pore space has been filled with water. This soil is referred to as being saturated, because at 45% volumetric water content, the soil can hold no more water.

In this experiment, you will gain experience using a Soil Moisture Sensor as you determine the volumetric soil water content of a soil sample. You will then investigate the water absorption properties of a sand/soil mixture.

Objectives

In this experiment, you will

• Learn to use a Soil Moisture Sensor.
• Determine the volumetric soil water content of a soil sample.
• Investigate the water absorption properties of a sand/soil mixture.
• Gain increased understanding of the role of soil moisture in ecosystems, watersheds, and the water cycle.