The impact of grazing management on soil properties and plant growth
Grazing is not just a traditional agricultural practice; it is essential for the economic and nutritional support of millions globally. It occurs on approximately 8.5 billion acres — almost half of the Earth’s terrestrial land — playing a pivotal role in food security and rural livelihoods.
These grazing lands are often located in regions unsuitable for intensive agricultural practices due to poor soil, steep slopes, or aridity, making grazing one of the few viable forms of land use in those places. Moreover, grazing supports a significant portion of the global meat and dairy industry and is crucial for the diets of billions.
The importance of these lands extends beyond food production; they are key reservoirs of biodiversity and provide essential ecosystem services such as water filtration, flood mitigation and carbon storage, all of which are crucial for environmental sustainability and climate regulation.
Grazing directly affects soil physical properties (such as bulk density and compaction), biogeochemical cycles (like carbon and nitrogen cycling) and biological functions (including soil microbial diversity and activity). Depending on the grazing intensity and management strategy, these impacts can either degrade or enhance soil health.
Different Grazing Systems
By tailoring grazing practices to the ecological feedback of specific environments, managers can harness grazing as a tool for environmental enhancement rather than degradation. This nuanced understanding of grazing’s potential impacts underscores the need for informed, adaptive management strategies that consider both the ecological health of grazing lands and their economic productivity.
Continuous Grazing
Continuous grazing is the simplest grazing management form, wherein livestock continuously graze the same area all year. This often leads to overgrazing, especially where vegetative recovery is slow, causing soil compaction from constant trampling. Compaction severely degrades the soil’s structure, reduces porosity, lowers water infiltration, and increases runoff and erosion, which also impairs water filtration near water bodies.
This degradation not only harms the land but also diminishes its agricultural productivity. Continuous grazing reduces soil organic carbon and total nitrogen, indicating worse soil health than in ungrazed or rotationally grazed areas. While initially cheaper, it incurs higher long-term costs due to increased feed needs and ongoing land maintenance.
Rotational Grazing
Rotational grazing is a strategic grazing method that divides a pasture into smaller paddocks, rotating livestock according to a planned schedule. This allows vegetation time to recover, enhancing ground cover, reducing soil erosion and improving water infiltration.
Rotational grazing has been shown to maintain or even increase soil organic carbon levels compared to continuous grazing, and it also reduces soil bulk density while improving structural quality and enhancing resilience to erosion. The periodic resting of paddocks promotes balanced root system development and nutrient cycling, boosting long-term soil fertility and plant health.
Although initial costs are higher, rotational grazing ultimately lowers long-term expenses by improving livestock productivity by 15-25 percent and forage efficiency by up to 30 percent, reducing the reliance on purchased feed.
Adaptive Multi-Paddock
Adaptive multi-paddock grazing is an advanced form of rotational grazing that involves intensive management to offer significant ecological benefits. This method involves closely monitoring grazing impacts and tailoring paddock rotation and rest periods to specific site conditions and ecological feedbacks. AMP grazing is designed to mimic natural grazing behaviors, with animals grazing intensely but briefly, followed by extended recovery periods for vegetation.
This strategy optimizes forage utilization and maintains high biodiversity levels both above and below the soil surface. It enhances soil health by improving organic matter content, boosting microbial activity, and promoting efficient water use through better soil structure. AMP grazing supports sustainable livestock production by fostering robust ecosystem functions and enhancing resilience against environmental stresses.
Despite higher initial costs and complexity, AMP grazing significantly improves economic returns by boosting livestock performance and pasture health, potentially increasing profitability by 20-35 percent.
Pasture Effects
The choice of grazing system plays a crucial role in determining the ecological and economic outcomes of livestock management. Transitioning from continuous to rotational or AMP grazing not only mitigates the adverse impacts on soil health but also enhances the productivity and sustainability of grazing lands. These systems require thoughtful implementation and ongoing adjustment to local conditions, emphasizing the need for skilled management and for understanding pasture ecology.
Effects of Grazing on Plant Responses
Grazing alters primary production by changing plant growth rates and biomass distribution across landscapes. Moderate grazing, often beneficial under the “grazing optimization hypothesis,” stimulates growth by reducing competition, promoting tillering, and enhancing light penetration, which increases photosynthetic activity by removing senescent plant material.
Animal movement redistributes nutrients through feces and urine, creating high nutrient concentrations especially around favored resting spots and significantly affecting nutrient cycling. Grazing impacts the soil microbial community, which is essential for decomposing organic matter and nutrient cycling. Properly managed grazing enhances nutrient cycling by increasing organic matter turnover and improving soil aeration through hoof action, thereby boosting plant nutrient uptake and soil fertility. However, excessive grazing can disrupt microbial communities and lead to nutrient leaching, particularly in wet conditions, reducing the availability of key nutrients like nitrogen and phosphorus.
Grazing also influences plant species composition by reducing the dominance of certain species and allowing less competitive ones to thrive, thereby enhancing biodiversity in managed grazing systems. Biodiverse plant communities are more resilient to environmental stresses such as drought and provide stable, varied habitats for wildlife. Thus, managing grazing to promote plant diversity is crucial for maintaining healthy and productive ecosystems.
Soil Carbon Sequestration
Soil carbon sequestration is critically influenced by grazing practices, which affect both the quantity and quality of plant inputs and soil organic matter turnover.
A global meta-analysis examining the impacts of grazing on soil health indicators found that continuous grazing often resulted in a significant reduction in soil organic carbon, with a mean effect size showing a decrease of SOC by about 0.08 units compared to no-grazing scenarios. In contrast, rotational grazing demonstrated a 0.25-unit increase compared to continuous grazing, suggesting improved carbon storage capabilities under rotational management regimes. These effects are attributed to better ground cover and enhanced root biomass in rotational systems, which help to maintain or increase soil organic matter.
Soil Organic Matter Accumulation
Soil organic matter (SOM) is fundamental to soil health, influencing nutrient availability, water retention and soil structure. Grazing affects SOM dynamics by altering plant productivity and the physical soil environment.
According to studies, managed rotational and AMP grazing systems have been shown to facilitate significant increases in SOM by promoting more balanced plant growth and allowing periods for vegetation recovery. These practices also increase ground cover and organic residue on the soil surface, which are crucial for protecting the soil against erosion and for promoting the incorporation of organic materials into the soil matrix.
Water Infiltration and Retention
Water infiltration and retention are critical soil functions that affect plant availability to water and resilience to drought. Grazing management significantly influences these properties through its impact on soil structure and porosity. Studies have documented that rotational grazing improves soil structure by reducing compaction and increasing soil organic matter, which enhances pore space and infiltration rates.
For instance, research indicates that rotational grazing can lead to improved water infiltration rates by as much as 20-30 percent compared to continuously grazed systems. This improvement is largely due to the maintenance of a more robust grass cover and less soil compaction, which facilitates easier water penetration through the soil profile and better moisture retention. These effects are particularly pronounced in systems where grazing is carefully managed to avoid overgrazing at any time, thereby ensuring that the soil is never left bare and susceptible to crusting or sealing, which can severely reduce infiltration rates.
Testing and Tracking Your Progress
Understanding soil health begins with targeted, comprehensive soil testing, which provides a baseline and ongoing metrics for assessing the impact of grazing practices. Many of these metrics focus on soil components related to biology, such as carbon pools or nutrient cycling.
| Test | Description | Significance | Optimal Range | Measurement Method |
| Soil Organic Carbon (SOC) | Measures total soil carbon, indicating soil health and fertility | Enhances soil structure, nutrient availability and microbial activity | 2-6% of soil mass | Dry combustion method to quantify CO2 |
| Permanganate Oxidizable Carbon (POXC) | Assesses the labile soil organic carbon, reactive and easily decomposed | Crucial for rapid nutrient cycling and assessing grazing impacts | 100-300 ppm | Colorimetric method using potassium permanganate to measure changes in labile carbon |
| Particulate Organic Matter (POM) | Organic particles loosely bound in soil, larger than 53 micrometers | Responds quickly to management changes; affects nutrient sourcing and soil structure | 20-40 g/kg of soil | Sieving to isolate, then weighing for concentration |
| Mineral-Associated Organic Matter (MAOM) | Stable organic matter linked with soil minerals | Indicates long-term carbon storage potential; decomposes slower than POM | 1-3% of soil mass | Sieving for separation, followed by weighing to measure concentration |
| Soil Respiration | Measures CO2 production by soil organisms decomposing organic matter | Reflects microbial activity and overall soil health; higher rates indicate active biology | 60-120+ ppm/24-hour period | Capturing and quantifying CO2 from incubated soil samples |
| Bulk Density | Measures soil mass per unit volume | High bulk density suggests compaction, affecting porosity and root penetration | 1.1-1.6 g/cm³ | Drying and weighing a known volume of soil |
| Water Infiltration Rate | Measures how quickly water enters the soil | Essential for evaluating the impact of grazing on soil structure and compaction | More than 20 mm/hour | Using infiltrometers or ring infiltrometers to record water descent rate |
| Microbial Biomass | Evaluates living microbial content in the soil | Crucial for organic matter decomposition and nutrient cycling; influenced by grazing. | 2000+ ng/g; 40+ ng/µl | Phospholipid Fatty Acid Analysis or DNA for microbial content |
Field experiments validate the insights gained from soil testing by applying them in real-world settings, measuring a range of soil parameters before, during and after grazing interventions. These experiments are essential for testing the efficacy of different grazing strategies on soil health.
After establishing baseline data through soil tests and field experiments, systems simulation modeling can be an indispensable tool. It integrates diverse data sources — including climate conditions, soil characteristics, plant growth dynamics and animal behavior — to simulate potential outcomes of various grazing strategies. By adjusting variables such as grazing intensity, timing and paddock design, these models allow researchers and land managers to explore how different factors might influence soil properties over extended periods. Simulation modeling helps in forecasting the long-term effects of grazing on soil health, aiding in decision-making to optimize grazing practices for both sustainability and productivity.
Grazing Land Restoration Strategies
Reversing years of detrimental grazing practices is essential for enhancing the ecological health and productivity of grazing lands. Implementing diverse seed mixes like tall fescue and alfalfa, which improve soil structure and nutrient cycling, can break up compacted soil layers and increase soil organic matter. Tall fescue, seeded at 15-30 pounds per acre, and alfalfa at 15-20 pounds per acre, are particularly effective for these purposes.
Switchgrass and clovers enhance soil stability and fertility — switchgrass helps retain water and prevent erosion and is typically seeded at 4-6 pounds per acre, while nitrogen-fixing clovers, such as red clover (8-12 pounds per acre) and white clover (2-4 pounds per acre), suppress weeds and enrich the soil.
Drought-tolerant species like blue grama and buffalo grass, requiring minimal nutrients, conserve moisture and protect against erosion; these are suitable for arid regions. Species such as ryegrass and sorghum-sudangrass, which grow quickly and improve soil structure, are seeded at about 20-30 pounds per acre, quickly covering the ground and adding organic matter.
Combining these plantings with management practices like targeted grazing, mechanical removal of invasive species, and the implementation of erosion control structures like terraces and windbreaks, can significantly enhance soil health and reduce the impact of past overgrazing.
Conclusion
Grazing holds a profound influence on soil health, the responses of plant communities and the broader ecosystem, with these impacts varying significantly according to the grazing management strategies deployed. By effectively implementing optimal grazing practices — such as rotational and AMP grazing — soil properties are enhanced, plant vitality is improved and overall pasture productivity increases.
These improvements not only contribute to environmental sustainability but also bolster the economic viability of agricultural enterprises by optimizing livestock productivity and reducing costs associated with land degradation and feed.
Patrick Freeze is a soil health scientist, research and development manager, and technical specialist at Ward Labs. He earned his Ph.D. in soil chemistry from Washington State University where he studied soil health and heavy metal chemistry as a USDA NIFA Needs Fellow and in Thailand as a U.S. Fulbright Scholar.
