Effective Rainfall measures how much rainfall contributes to plant growth. This guide explains its relationship with farm management, the role of evapotranspiration, and how the Effective Rainfall tool helps farmers optimise water use and soil health
1. Effective Rainfall – What Is It and How Management Can Increase It?
What Is Effective Rainfall?
Effective rainfall refers to the portion of total rainfall that is available for plant growth after accounting for losses due to runoff, deep drainage, and evaporation. In agricultural systems, not all rainfall directly benefits crops and pastures—some is lost before it can be used by plants. Factors such as management practices, ground cover, and soil type play a crucial role in determining how much rainfall becomes effectively available to support plant growth.
How Management Influences Effective Rainfall
Farmers can increase their effective rainfall by adopting practices that reduce losses and improve water infiltration. Key strategies include:
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Maintaining Ground Cover – Higher levels of vegetation or mulch prevent soil erosion and slow water movement, allowing more rainfall to be absorbed rather than lost as runoff.
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Improving Soil Structure – Practices like rotational grazing, minimal tillage, and organic matter incorporation enhance soil porosity, improving water retention and infiltration.
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Managing Stocking Rates – Avoiding overgrazing preserves plant cover and root structures, helping to capture and store rainfall effectively.
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Optimizing Crop and Pasture Rotation – Diverse plant species with deep root systems increase water uptake and reduce unproductive losses.
The Connection Between Effective Rainfall, Management, and Soil Organic Carbon
Effective rainfall plays a crucial role in soil organic carbon (SOC) sequestration, as it directly influences plant productivity and microbial activity in the soil. Higher effective rainfall means greater plant biomass production, leading to increased root exudates and organic matter inputs into the soil. This, in turn, supports microbial communities that drive soil carbon storage. By improving ground cover and soil structure to maximize effective rainfall, farmers can actively influence their soil carbon levels, countering claims that soil carbon sequestration is solely dependent on environmental factors such as gross rainfall. This puts the power back into the hands of producers, emphasizing that management decisions play a critical role in soil health and carbon storage.
(source: Savory Institute (2020))
2. Evapotranspiration – What Is It and How to Boost Plant Transpiration
What Is Evapotranspiration?
Effective Rainfall is quantified through measures of Evapotranspiration. Evapotranspiration (ET) is the combined loss of water from the land surface through evaporation (from soil and water bodies) and transpiration (energetic utilisation of water from plants). It represents the main pathway through which water returns to the atmosphere and is a critical component of the water cycle in agriculture.
How to Enhance Plant Transpiration for Productivity
The goal of farm water management is to maximize transpiration while minimizing non-productive evaporation. Strategies to achieve this include:
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Increasing Green Cover – More vegetation means higher transpiration and reduced direct evaporation from the soil.
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Managing Soil Moisture – Practices such as deep-rooted perennials, mulching, and controlled irrigation improve water retention, ensuring plants have access to moisture for transpiration.
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Reducing Bare Soil Exposure – Bare soil leads to higher evaporation losses; maintaining living or non-living ground cover helps retain moisture for plant use.
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Selecting a Diversity of Efficient Crop and Pasture Species – Some plants are more water-efficient, meaning they transpire effectively while using less water.
By using the Effective Rainfall tool, farmers can make informed decisions to maximize their available water, ensuring better resilience against drought and improved productivity in their farming systems.