Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key terms like carrying capacity and grazing systems.
• Calculate the carrying capacity of a pasture.
• Evaluate different grazing systems for South African farms.
• Explain techniques to improve pasture quality.
• Analyze the impact of overgrazing and how to prevent it.

Lesson summary

South Africa's livestock industry is a vital part of our economy, contributing significantly to food security and livelihoods, particularly in rural communities. Effective pasture and fodder production is fundamental to the success of this industry. Poor pasture management leads to overgrazing, soil erosion, and reduced livestock productivity. This week, we will delve deeper into the principles of pasture management, focusing on grazing systems, carrying capacity, and improving pasture quality. Understanding these concepts will equip you with the knowledge to manage pastures sustainably and improve livestock production.

Lesson notes

2. 1. Grazing Systems A grazing system is a planned approach to managing livestock grazing on pastureland. The primary goal is to optimize pasture utilization while maintaining or improving pasture health and productivity. There are several common grazing systems, each with its own advantages and disadvantages: Continuous Grazing: Livestock have unrestricted access to the entire pasture area throughout the grazing season.

Advantages:* Simple to manage, requires minimal infrastructure.

Disadvantages:* Can lead to overgrazing of preferred plant species and under-utilization of less palatable species. Increases soil compaction in certain areas.

Rotational Grazing: The pasture is divided into several paddocks, and livestock are moved between these paddocks on a planned schedule. This allows grazed paddocks to rest and recover.

Advantages:* Improves pasture utilization, promotes even grazing, enhances plant recovery, reduces soil erosion, and controls parasites.

Disadvantages:* Requires more infrastructure (fencing, water systems), more intensive management.

Strip Grazing: Livestock are given access to a narrow strip of pasture each day, usually using temporary fencing. This maximizes forage utilization and minimizes wastage.

Advantages:* Very efficient use of forage, reduces selective grazing, promotes even distribution of manure.

Disadvantages:* Requires daily management, can be labor-intensive, not suitable for large herds.

Deferred Rotational Grazing: Some paddocks are rested (deferred) during critical plant growth periods, allowing them to fully recover and set seed.

Advantages:* Improves pasture vigor and seed production, enhances biodiversity.

Disadvantages:* Requires careful planning and monitoring, may reduce available grazing area in the short term. 2.

2. Carrying Capacity Carrying capacity is the maximum number of livestock that can be grazed on a given area of pasture without causing damage to the pasture or soil. It is typically expressed in terms of Animal Units (AU) per hectare. An Animal Unit is generally defined as a 450 kg cow with a calf.

Factors affecting carrying capacity: Pasture productivity (influenced by rainfall, soil fertility, plant species). Livestock size and type (cattle, sheep, goats). Grazing system. Climate. Management practices.

Calculating Carrying Capacity: Estimate Pasture Yield: Determine the amount of usable forage produced per hectare. This can be done by clipping and weighing samples of pasture vegetation, or by using published data for similar pasture types in the region.

Estimate Forage Intake: Determine the daily forage intake of the livestock. A general rule of thumb is that livestock consume approximately 2.5-3% of their body weight in dry matter per day.

Calculate Total Forage Required: Multiply the daily forage intake by the number of livestock and the length of the grazing season.

Calculate Carrying Capacity: Divide the total pasture yield by the total forage required.

Example: A farmer has 10 hectares of pasture. The estimated pasture yield is 4000 kg of dry matter per hectare per year. The farmer wants to graze cows weighing 500 kg each for 180 days.

Pasture Yield: 10 hectares * 4000 kg/hectare = 40000 kg Daily Forage Intake per Cow: 500 kg * 0.025 (2.5%) = 12.5 kg Total Forage Required per Cow: 12.5 kg/day * 180 days = 2250 kg Carrying Capacity: 40000 kg / 2250 kg/cow = 17.77 cows Therefore, the carrying capacity of the pasture is approximately 17 cows. It is critical to not exceed this number, or ideally, to graze slightly below it to allow for pasture regeneration and prevent overgrazing. 2.

3. Overgrazing Overgrazing occurs when livestock graze plants faster than they can regrow, leading to a decline in pasture productivity, soil erosion, and reduced biodiversity.

Consequences of Overgrazing: Reduced pasture yield. Soil erosion and compaction. Loss of desirable plant species. Increased invasion of weeds and undesirable plants. Decreased water infiltration. Increased runoff and sedimentation. Lower livestock productivity.

Preventing Overgrazing: Maintain stocking rates below the carrying capacity. Implement rotational grazing systems. Monitor pasture condition regularly. Adjust grazing management based on seasonal conditions. Provide supplemental feed during periods of drought or low pasture availability. 2.

4. Pasture Improvement Techniques Fertilization: Applying fertilizers (nitrogen, phosphorus, potassium) to improve soil fertility and increase pasture yield. Soil testing is crucial to determine the specific nutrient needs of the pasture.

Reseeding: Introducing new, improved pasture species to enhance productivity and palatability. This may involve complete renovation of the pasture or overseeding existing pastures.

Weed Control: Controlling weeds that compete with desirable pasture plants for resources (water, nutrients, sunlight).