Available water capacity (AWC) – Definition & Detailed Explanation – Soil & Fertilizers Glossary

I. What is Available Water Capacity (AWC)?

Available Water Capacity (AWC) is a term used in soil science to describe the amount of water that can be stored in the soil and is available for plant uptake. It is a crucial parameter for understanding the water-holding capacity of soil and plays a significant role in determining the growth and productivity of plants. AWC is typically expressed as the volume of water that can be held in a specific depth of soil, such as inches or centimeters.

II. How is Available Water Capacity (AWC) measured?

AWC is measured by conducting a soil water retention curve, also known as a soil moisture characteristic curve. This curve is generated by subjecting soil samples to different levels of suction or pressure and measuring the corresponding water content at each pressure level. The data obtained from this curve can be used to calculate the AWC of the soil by determining the range of water content between field capacity (maximum water-holding capacity) and permanent wilting point (minimum water content at which plants wilt).

III. What factors influence Available Water Capacity (AWC)?

Several factors influence the AWC of soil, including soil texture, organic matter content, soil structure, and compaction. Soil texture refers to the relative proportions of sand, silt, and clay particles in the soil, with clay soils typically having higher AWC than sandy soils due to their smaller particle size and higher surface area. Organic matter content also plays a significant role in AWC, as organic matter acts as a sponge, holding onto water and increasing the soil’s water-holding capacity. Soil structure, which refers to the arrangement of soil particles into aggregates, can affect AWC by influencing water infiltration and retention. Compaction, caused by heavy machinery or foot traffic, can reduce AWC by decreasing pore space and limiting water movement through the soil.

IV. Why is Available Water Capacity (AWC) important for plant growth?

AWC is crucial for plant growth and productivity because it determines the amount of water available to plants for uptake through their roots. Adequate AWC ensures that plants have a constant supply of water, which is essential for photosynthesis, nutrient uptake, and overall growth. Insufficient AWC can lead to water stress in plants, resulting in wilting, reduced growth, and lower yields. By understanding and managing AWC in the soil, farmers and gardeners can optimize water use efficiency and promote healthy plant growth.

V. How can Available Water Capacity (AWC) be improved in soil?

There are several ways to improve AWC in soil, including adding organic matter, improving soil structure, reducing compaction, and implementing irrigation and drainage practices. Adding organic matter, such as compost or manure, can increase AWC by improving soil structure, increasing water retention, and promoting microbial activity. Improving soil structure through practices like reduced tillage and cover cropping can also enhance AWC by creating larger pore spaces for water storage and movement. Reducing compaction through practices like controlled traffic farming or using cover crops can help increase AWC by allowing for better water infiltration and root growth. Implementing irrigation and drainage systems can also help maintain optimal AWC levels by providing water when needed and preventing waterlogging.

VI. What are the implications of low Available Water Capacity (AWC) in soil?

Low AWC in soil can have significant implications for plant growth and productivity. When AWC is limited, plants may experience water stress, leading to wilting, reduced nutrient uptake, and stunted growth. Low AWC can also increase the risk of crop failure during periods of drought or water scarcity, as plants may not have access to enough water to survive. In addition, low AWC can result in poor soil health, as it can lead to increased erosion, nutrient leaching, and compaction. By understanding the implications of low AWC and taking steps to improve soil water-holding capacity, farmers and gardeners can ensure healthy plant growth and sustainable land management practices.