Why does plant available water increase as particle size decreases

The availability of water is a crucial factor that determines the growth and survival of plants. As such, farmers and gardeners must ensure that their plants have sufficient water for them to thrive. One major factor that plays a role in the availability of water to plants is the particle size of the soil. In this article, we will explore the relationship between particle size and plant available water, and why plant available water increases as particle size decreases.

Understanding Soil Particle Size

Soil particle size refers to the size of individual particles that make up the soil. The three main categories of soil particles are sand, silt, and clay. Sand particles are the largest, with sizes ranging from 0.05mm to 2mm. Silt particles are smaller, ranging from 0.002mm to 0.05mm, while clay particles are the smallest, with sizes less than 0.002mm.

Water Holding Capacity of Soil

The ability of soil to hold water is known as its water holding capacity. The water holding capacity of soil is affected by several factors, including particle size, organic matter content, and soil structure. Soils with smaller particle sizes have higher water holding capacities as they have more surface area that can hold onto water. In contrast, soils with larger particle sizes have lower water holding capacities as they have less surface area to hold onto water.

Water Movement in Soil

Water moves through soil in two ways: gravitational water movement and capillary water movement. Gravitational water movement occurs when water enters the soil and drains through it due to gravity. Capillary water movement occurs when water is held by the soil's surface tension and moves upward through the soil. This movement is due to the small spaces between soil particles, known as pores.

Effect of Particle Size on Water Movement

The size of soil particles affects the size of the pores in the soil. Soils with smaller particle sizes have smaller pores, which means this soil can hold onto water for longer periods. Soils with larger particle sizes have larger pores, which means that they cannot hold onto water for as long. This is because water moves through larger pores more easily due to gravity, leading to gravitational water movement.

Relationship between Particle Size and Plant Available Water

The amount of water that is available for plants in the soil is known as plant available water. This water is needed for plant growth and survival. As previously stated, soils with smaller particle sizes have higher water holding capacities, which means they can retain more water. This leads to more plant available water being present in the soil. In contrast, soils with larger particle sizes have lower water holding capacities, which means they can retain less water, leading to less plant available water.

Conclusion

In conclusion, the relationship between particle size and plant available water is an important factor that must be considered by farmers and gardeners. Soils with smaller particle sizes have higher water holding capacities and can retain more plant available water than soils with larger particle sizes. Understanding the water holding capacity of soil is important when planning for irrigation, choosing plants to grow, and improving soil health.