Partial Measurement in Pasture Assessment

Partial Measurement Overview

• Focus on indirect or nondestructive methods of measuring pasture mass on farms.
• Alternatives to direct cutting methods are cheaper and easier.

Methods for Measuring Pasture Mass

• Visual Assessment

  • Cheapest and quickest method for measuring pasture mass.
  • Requires practice for accurate estimates.
  • Essential for farmers to quantify assessments in kilograms of dry matter per hectare.

  Advantages:

  • Fast and simple.
  • Can visually assess large sample sizes and areas.
  • Applicable to various types of pastures, including hill country.

  Limitations:

  • Inconsistency between different observers.
  • Requires calibration to improve accuracy.
  • Difficult to see all botanical components, which may differ in dry matter content and nutritional values.

Calibration Process

• Calibrate by setting visual benchmarks of known mass/composition across a range from low to high pasture mass.
• Visual assessment accuracy of around ±100 kg dry matter per hectare requires calibration.

Visual Assessment Techniques

• Use visual benchmarks for calibration, including:
  • Quadrats with known area to cut and assess herbage mass.
  • Regularly check and benchmark visual assessments against actual cuts to ensure consistency.

Example of Calibration

• Example data indicates different dry matter content at different heights.
  • E.g., samples varied widely in height (e.g., 2.5 cm could show ~200 kg/ha to 15 cm might show ~2,200 kg/ha).

Botanical Composition Analysis

• Assessment of component composition (e.g., clover, grass, dead material, etc.) is necessary for effective management.
• Understanding proportions of clover can impact estimations of crude protein values:
  • Example: 15% clover contributes high ME value compared to grasses.

Tools for Measuring Pasture Mass

• Sword Sticks or Ruler:

  • Measure height and relationships to pasture mass.

• Rising Plate Meter:

  • Measures height and density of pasture.
  • Accounts for variations in pasture density to improve accuracy of estimates.

• Capacitance Probes:

  • Measure electrical conductivity of pasture components.
  • Allow for rapid measurement but may require calibration for accuracy.

Important Notes on Tools

• Calibration is vital for accuracy with all these tools.
• Direct comparison to actual pasture cut mass establishes relationships for future estimates.

Estimating Pasture Productivity

• Grazing Days Calculation:
  • Number of animals x number of days in a paddock determines productivity per hectare.
  • Example: 500 ewes grazed for 4 days in a paddock would yield 2000 grazing days.

Summary of Techniques and Their Application

• Various methods exist with different sophistication levels:
  • Visual assessments (simple) to sophisticated electronic tools (expensive).
  • Calibration against actual dry mass cuts improves reliability.
  • Use of knowledge of ME values of pasture components to visually assess quality and manage grazing effectively.

Importance of Consistent Calibration

• It's recommended to calibrate tools regularly (about five times during the growing season) to adjust for changing botanical compositions and dry matter contents.
• These adjustments are crucial for the accuracy of indirect measurement methods used by farmers.