December 16, 2024 by Lachie

Legumes in Your Pasture: Why 30% is the Ideal Proportion

Legumes play a key role in creating a profitable, productive, and sustainable pasture system. They contribute to higher livestock weight gains, improve soil fertility, and enhance paddock health—making them an essential component of any successful grazing system.

But how much legume is the right amount? While this may vary depending on your grazing goals—for instance, you might not be best to target 30% legumes in a system applying 500 units of nitrogen fertiliser per hectare—However, research and experience consistently shows that a good proportion to strive for is 30% of your paddock to be legume, this strikes the perfect balance between productivity and sustainability.

In this blog, we’ll explore:

• Why 30% is the ideal proportion
• The benefits of maintaining this balance
• The risks of allowing legumes to dominate

Why Aim for 30% Legumes?

The 30% target is a widely recommended proportion because it provides the best of both worlds: a balance that boosts pasture performance while avoiding the challenges associated with legume-dominated systems. Here’s why:

1. Improved Livestock Weight Gains

Maintaining 30% legumes in your pasture significantly improves livestock performance due to higher protein and metabolisable energy (ME) content found in most legumes.

Why It Matters:

• Higher Protein Content: Legumes provide crude protein (CP), the essential building blocks for muscle development and growth.
  • Particularly valuable for:
    • Young, growing livestock
    • Lactating females with high nutritional demands.
• Metabolisable Energy (ME): Legumes deliver higher energy levels than grasses, enabling livestock to meet energy requirements for:
  • Weight gain
  • Milk production
  • Reproductive performance

Real-World Benefits

Research consistently demonstrates the impact of legumes on livestock weight gains:

1. Higher Daily Gains:
   • Livestock grazing on legume-rich pastures achieve higher average daily gains (ADG) compared to grass-only systems.
   • Example: Incorporating legumes like Desmanthus spp., Sytlostanthes spp., butterfly pea has shown measurable increases in weight gain.
2. Improved Feed Efficiency:
   • With legumes providing superior nutrition, livestock can convert feed to weight gains faster, improving:
     • Time to market for beef and lamb producers.
     • Overall profitability of grazing operations.

Supporting Research and Resources:

• B.NBP.0765 Final Report on Legumes in Northern Grazing Systems
• MLA Feedbase Hub: Legume Benefits for Livestock
• Beef Production Benefits of Legumes at Wandoan

2. Nitrogen Fixation

• Legumes have a unique ability to fix atmospheric nitrogen in the soil through symbiotic bacteria in their root nodules. Choosing the correct Rhizobia strain is key to getting the most out of legumes/fixation.
• At 30%, legumes are likely to provide adequate nitrogen levels to support companion grasses’ growth, thus boosting dry matter production and nutritive value.

Above: Nodulation on a 4-week-old Butterfly Pea (Clitoria ternatea) seedling (Explore more with the Pasture Picker →). While these nodules are mostly inactive (white colour), they highlight the critical symbiotic relationship between rhizobia bacteria and legumes. This relationship allows legumes to fix atmospheric nitrogen, enhancing soil fertility and supporting productive pasture performance.

Further Reading:

• How to assess legume nodulation →
• Nodulation Fact Sheet →
• MLA Research on Nodulation and Pastures →
• Tips and Tactics for Legumes and Nitrogen Fixation →

3. Optimised Pasture Productivity

• Research has shown that pastures with around 30% legumes produce higher overall dry matter yields.
• Legumes complement grasses rather than outcompeting them, creating a diverse and productive forage base.

4. Resilience to Climate Variability

A pasture with a mix of grasses and legumes is far more resilient to changing weather conditions.

• Drought Tolerance: Legumes, such as desmanthus, clover, and lucerne, often withstand dry conditions better than grasses. They provide critical forage when grasses are under stress.
• Long-term Productivity: The nitrogen fixed by legumes supports companion grasses, ensuring continued regrowth after dry periods or heavy grazing.

In short, 30% legumes create a pasture system that can adapt to the challenges of climate variability.

What Happens If You Exceed 30% Legumes?

While legumes offer numerous benefits, an excess can lead to several challenges:

1. Risk of Bloat

• Legumes such as clover and lucerne (alfalfa) (more temperate) can cause frothy bloat in cattle and sheep due to their high soluble protein content.
• Keeping legumes at around 30% significantly reduces this risk while still providing their nutritional benefits.

2. Nutritional Imbalance

• Legume-dominant pastures may lead to excessive protein intake, which can result in ruminal acidosis and inefficient nitrogen utilisation by livestock. Note that many tropical legumes have higher tannin levels which enables the protein to bypass the rumen which increases protein utilisation in the true stomach of ruminants.

3. Competition with Grasses

• If legumes exceed 30%, they may be more dominant than grasses. This is less desirable in lower rainfall periods or regions with a distinct dry season, whereas legumes tend to lose their leaves during dry periods, leading to reduced forage availability. In contrast, grasses provide valuable dry feed that sustains livestock when fresh forage is scarce.

How to Maintain the Right Proportion?

Achieving and maintaining 30% legumes in your pasture requires careful management. Here are some practical tips:

1. Choose the Right Legume Species

• Different legumes thrive in different climates and soil types. For example:
  • Tropical Pastures: Consider Desmanthus spp., Stylostanthes spp., butterfly pea or Centrosema spp.
  • Temperate Pastures: Subterranean clover, white clover, or lucerne work well.
• Explore more with the Pasture Picker → Select legumes that complement your pasture goals and conditions.

2. Monitor Your Pasture Composition

• Regularly assess the proportion of legumes in your paddock through plant counts or visual estimates.
• If legumes fall below 20% or exceed 40%, consider adjusting your grazing strategy (length, stocking rate) or possibly reseeding.

3. Implement Rotational Grazing

• Rotational grazing enables optimal grazing management. Ensuring legumes are utilised in their optimal nutritive period although not grazing legumes out. This ensures high livestock weight gains and long term paddock/pasture productivity.
• It also promotes even utilisation of the pasture and encourages regrowth.

4. Avoid Over-Fertilising

• Excess nitrogen fertiliser can suppress legume growth, while nutrients such as phosphorus and sulphur fertiliser can encourage legume establishment. Apply fertilisers based on soil test results or advice from an agronomist.

5. Graze Strategically

• Grazing during periods of rapid legume growth aids utilisation and control of legume dominance and maintain balances.

The Bottom Line: Balance is Key

Legumes are an invaluable component of any pasture system, but balance is crucial. By maintaining approximately 30% legumes in your paddock, you can enjoy the benefits of improved soil fertility, better livestock gains/nutrition and higher pasture productivity without the risks of legume dominance.

Whether you’re managing cattle, sheep, or mixed livestock, the 30% rule ensures a diverse, sustainable, and productive pasture that works in harmony with your farming goals.

Take Action

Ready to optimise your pasture? Use our Pasture Picker Tool to find the perfect legume-grass mix for your region. It’s quick, easy, and tailored to your farm’s conditions.

Explore the Pasture Picker Now!