Understanding soil moisture constants along with soil type and crop water needs, are crucial factors for making informed irrigation decisions. There are four important soil moisture constants that we need to consider when determining the best time to irrigate: field capacity, wilting point, available water capacity and saturation capacity:
- Field capacity: This is the amount of water remaining in the soil after excess water has drained away. The water held at this point is easily accessible for plant uptake.
- Saturation Capacity: This is the maximum amount of water the soil can hold when all pores are completely filled with water.
- Wilting Point: This is the water content at which plants can no longer extract water from the soil and begin to wilt permanently. It represents the lower limit of water available for plants.
- Available Water Capacity (AWC): This is the amount of water held between ‘field capacity’ and ‘wilting point’. The AWC is the most important factor in determining how much water is available for plants and influences the decision of irrigation.
These soil Moisture Constants can help with irrigation decisions:
Determining Irrigation Trigger Points: Irrigation should ideally be initiated before the soil moisture drops to the permanent wilting point.
Optimising Irrigation Depth: By understanding the water holding capacity of the soil and the root zone depth, we can determine the appropriate amount of water to apply during each irrigation event.
Determining Irrigation Strategies: Different crops and soil types have different water requirements and sensitivities to water stress. Soil moisture monitoring allows for customized irrigation strategies based on these factors.
Preventing Over- and Under-Irrigation: Monitoring soil moisture helps to avoid overwatering, which can lead to waterlogging and nutrient leaching, as well as underwatering, which can cause plant stress and yield reductions.
Improving Water Use Efficiency: By applying the right amount of water at the right time, we can minimize water waste and maximize water use efficiency.
Meeting Compliance Requirements: Soil moisture monitoring can provide valuable data for demonstrating responsible water management practices and meeting environmental regulations.
Natalia Zefferino
Evironmental Consultant