Summary of Pasture Irrigation Principles and Management

Principles of Pasture Irrigation

Irrigation can significantly affect forage yield and persistence. Excessive irrigation leaches nutrients and can lead to water quality problems. Insufficient irrigation causes drought stress, raising nitrate levels in plants, which is hazardous to livestock.

Function of Water in Plants

Water is essential for plants, constituting 70-90% of their tissues. It supports photosynthesis, nutrient transport, and temperature regulation. Stomata control water evaporation, and water must be available in the soil for root absorption.

Key Terms in Pasture Irrigation

  • Available Soil Water (AW): Difference between field capacity and permanent wilting point; indicates water that plants can use.

  • Water-Holding Capacity (WHC): Soil's ability to retain moisture.

  • Evapotranspiration (ET): Total water loss from evaporation and plant transpiration.

  • Field Capacity (FC): Water content when soil is saturated and free drainage occurs.

  • Permanent Wilting Point (PWP): Soil moisture level at which plants cannot recover.

  • Management Allowable Depletion (MAD): Fraction of AW that can be used before plant growth declines, typically 50%.

  • Readily Available Water (RAW): Portion of AW usable by plants without yield penalties.

Irrigation Management

Efficient water management improves forage production. AW helps schedule irrigation based on soil texture and structure. Sandy soils have less AW, while clay soils have more. Plant roots can extend to varying depths, impacting water uptake.

Types of Irrigation Systems

  • Surface & Flood Irrigation: Simple methods but may require more labor and have lower efficiency.

  • Sprinkler Systems: More efficient in water use, better suited for sloping areas.

  • Center Pivot Systems: Overhead systems suitable for large areas but more expensive.

  • Line Pod Systems: Flexible and easy to maintain; suitable for various scales.

Factors for Effective Irrigation

Understanding soil texture and rooting depth is crucial for irrigation planning. Overwatering can damage crops and increase costs, while underwatering reduces yields. Plant observation, soil feel, and moisture monitoring devices aid in effective scheduling.