Grazing Management Effects on Pasture Growth and Quality

Grazing management is about making the best use of pasture so that both livestock and the grassland can thrive. The goal is to find a balance where livestock have enough food while the pasture remains healthy and continues to grow well.

Historical Context

In 1955, Ray Brom highlighted the need to understand how grass recovers after being grazed. Knowing how grass grows between grazing helps make better management decisions.

Key Researcher: Ray Brom

Ray Brom did important research on how to manage pastures effectively at DSIR Palmerston North, New Zealand. He studied how different grazing methods affected mixtures of grasses and clover. One of his key findings was how to measure the amount of grass after it has been grazed, leading to the discovery that grass grows in a predictable pattern.

Pasture Growth Rate Dynamics

After grass is grazed, it doesn’t grow much at first. Then, it grows quickly, and eventually, its growth slows down again. Brom identified three growth phases:

• Phase 1: Slow growth right after grazing.

• Phase 2: Rapid growth when conditions are good.

• Phase 3: Growth slows as maximum grass yield is reached.

Factors Influencing Pasture Growth

• Stored Reserves: The amount of carbohydrates in roots and grass stems after grazing is essential for recovery.

• Soil Moisture: Even when there's enough water, grass might not thrive if it doesn't have enough leaves.

• Light Interception: Grass needs proper leaf area to capture sunlight for photosynthesis; fewer leaves mean less light absorption.

Effects of Grazing Height

The height at which grass is cut matters. Grazing too low prolongs the slow growth phase (Phase 1), which is not ideal. The best height for encouraging regrowth is around 5 inches, as this helps the grass capture more sunlight.

Leaf Area Index (LAI) and Growth

The amount of leaf area is crucial for grass regrowth; an LAI of around 5 is necessary for optimal light capture. Managing to maintain this LAI maximizes grass growth through effective photosynthesis.

Phase Two Growth Factors

• Competition: Other plants may compete for light and nutrients, slowing down grass growth.

• In older pastures, shading from taller plants can hinder grass regrowth.

Nutrient Requirements

More grass means higher nutrient needs, especially nitrogen. For instance, if a pasture produces 3 tons of hay per hectare with 4% nitrogen, it needs about 120 kg of nitrogen.

Grazing Management Systems

Brom’s experiments compared different grazing systems based on how often and hard animals grazed to see how it affected total grass production. Keeping pastures in the fast growth phase is key to providing nutritious feed for livestock.

Grazing Height Effects from Later Studies

Later research looked into how continuous grazing versus rotating pastures influences growth. An ideal grass mass is found to be 1000 to 1500 kg dry matter per hectare for optimal growth, keeping the grass about 3-5 cm tall.

Pasture Quality Considerations

How we manage grazing impacts the types of plants in a pasture and their energy value for livestock. Leafy pastures often offer more energy than fibrous, taller ones. Understanding the best energy values and conditions is vital for effective livestock feeding.

Conclusion

Good grazing management is essential for keeping pastures healthy and ensuring livestock get enough nourishment. Focus on maintaining pastures in the fast growth phase while managing how much and how often animals graze to support efficient livestock production.