Rotational grazing boosts water use

U of A researchers determine that adopting adaptive multi-paddock grazing improves water infiltration in grassland soil

Over the past five years, a group of scientists at the University of Alberta conducted a research study to better understand how rotational adaptive grazing management across Western Canada influences environmental processes.

They have demonstrated that adaptive grazing improves soil water infiltration in temperate grasslands compared to conventional grazing practices.

In a published paper, the researchers found that adaptive multi-paddock grazing (AMP) improves water infiltration in grassland soils.

The scientists concluded that giving plants sufficient time to recover from grazing activities in the growing season had substantial benefits for soil water infiltration. In contrast to extended rest, direct animal impacts including cattle stocking rate showed minimal or even negative impacts on infiltration.

However, water infiltration was only one component of a bigger study that also looked at carbon sequestration.

“This was the main hook for conducting the study because there’s so much interest in soil carbon at the moment at the science level and different stakeholder levels,” said Timm Döbert, a post-doctoral fellow at the U of A and part of the research team.

“Our idea was to look at this in the first place, but then appreciating that soil carbon is driven by vegetation, water, enzymes and microbes. So we have a lot of different response variables,” he said.

The researchers caution that intensified efforts are needed to end the ongoing conversion and degradation of natural ecosystems around the globe. Safeguarding and restoring grasslands and forests provides a cost-effective, nature-based solution for stabilizing the climate, ensuring food security and preserving ecosystem services, they said.

AMP describes a high intensity type of grazing. Instead of a conventional large ranch or one large paddock where cattle roam freely, a rotational system is set up using many small paddocks where cattle graze at a high density for short periods of time.

Applied Ecological Services staff use a hydraulic soil sampler mounted on an all-terrain vehicle to extract soil cores up to one metre deep. They are then processed in the lab to determine soil organic carbon and other soil attributes. | Applied Ecological Services/Patrick Daniels photo

“The fundamental ideas of this are using high density grazing and giving extensive rest afterwards. So these are the fundamental pillars and it’s related to holistic grazing management,” said Döbert.

The problem with conventional grazing practices, he said, is that there is not adequate time for plants to regenerate because animals often prefer to eat certain plants, which they continue to focus on in the same season. It depends partly on the size of the paddocks, the resource availability and the strategy of the farmer.

However, adaptive multi-paddock grazing puts more pressure on the land for shorter periods of time, which allows grass the opportunity to regenerate.

More than 60 beef producers participated in the study throughout the Prairies, which Döbert said was unusually large.

“What’s really unique about this study is it’s not just the scope — that we’re actually looking at more than 60 ranches in total, where most studies normally have maybe a handful of studies,” he said.

Researchers say adaptive multi-paddock grazing puts more pressure on the land for shorter periods of time, which allows grass the opportunity to regenerate. | Timm Döbert photo

“Most studies also just look at a grazing system. So they say this is (adaptive multi-paddock) grazing and this is not AMP grazing, but they don’t necessarily account for a lot of variation at the producer level.”

Half of the ranches were under the adaptive multi-paddock grazing, which is a type of high-intensity rotational grazing.

Characteristics of this grazing system are high animal unit densities, small paddocks, and short periods of grazing followed by a long rest period.

Each adaptive multi-paddock grazier was matched with a ranch neighbour using more conventional grazing.

A few ranch neighbours used continuous grazing, while the majority employed rotational grazing at low intensities.

The sample of ranch neighbours was representative for Western Canada, where about 80 percent of graziers use some form of rotational grazing but only five to 10 percent would be considered adaptive multi-paddock graziers.

Researchers use a variety of equipment to measure water infiltration in the field. | Applied Ecological Services/Patrick Daniels photo

On each ranch, university students collected soil and vegetation samples, measured greenhouse gases and water infiltration and counted birds.

Some of the soil and vegetation samples had to be processed and analyzed in the laboratory at the university, for example, to get the amounts of organic carbon in each soil sample. Data from all the samples was then analyzed using statistical methods.

The main goal was to test if there were overall differences between pastures managed by the adaptive multi-paddock grazers and their ranch neighbours.

However, it was also important to collect specific information on grazing practices from each rancher because no two ranchers manage their herds in exactly the same way.

These details included data on the number of cattle, the length of typical grazing periods and the duration of rest between grazing events.

Overall, the study is providing new insights on how variation in grazing management can influence plant productivity, soil carbon storage, greenhouse gas emissions and wildlife habitat.

The researchers found that adaptive multi-paddock grazing improved the infiltration of water into the soil, which was mainly attributed to extended periods of rest and plant recovery following early-season cattle grazing.

A Dual Head Infiltrometer measures the ease with which water moves into the soil and provides a vertical flow rate metric. | Applied Ecological Services/Patrick Daniels photo

However, there was no evidence that grazing cattle at higher densities or greater numbers would be beneficial for water infiltration.

As expected, more compacted soils had a negative impact on water infiltration. In contrast, build-up of dead plant material on top of the soil increased the flow of water into the soil of adaptive multi-paddock ranches.

“If we can adopt certain changes like a longer rest period, then this might be very beneficial for having more water. It stimulates more productivity, which is good for the producer, but at the same time reduces the carbon footprint. So we’re sparking some ideas of what could be done,” he said.