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When you can’t turn off the rain

Serkan Ates and David Hannaway for Progressive Forage Published on 01 March 2020

Pastures provide an inexpensive source of high-quality feed for livestock and have a positive impact on soil- and water-related processes.

A temperate climate and the winter-dominated precipitation conditions of western Oregon are highly conducive to vegetation growth during the cool season. However, good management of pastures does not come without challenges.

Temperature and precipitation are the main governing factors affecting pasture growth and producers’ grazing plans. High rainfall combined with a slowly draining soil type makes grazing challenging at the time when forage plants are in their optimal nutritional stage. Soil type and soil health are huge factors in both the production of forages and grazing planning.

The soil type and conditions at the time of grazing interact with the extent of trampling and dictate the required recovery period. Clay soils can be a fertile medium of forage species growth but are not ideal for grazing in early spring due to slow drainage and resulting waterlogging. In addition, these soils tend to have a low pH, limiting species selection or requiring liming.

Effect of livestock on soil health

Grazing livestock have significant effects on plant growth, soil health and nutrient cycling. Intensive grazing can result in soil pugging (damage caused by livestock hooves) and compaction, severely damaging soil structure and plant regrowth over time. Deterioration of soil health is more severe under waterlogged and compacted soil conditions due to poor aeration and animal trampling. Degraded grazing systems can result in significant losses of soil organic carbon (SOC) and increases in greenhouse gas (CO2 and CH4) emissions. However, destocking to avoid pugging damage typically leads to low pasture utilization and accumulation of more stemmy forages in the late spring/summer period, resulting in poor-quality forage and reduced legume content.

Without grazing or mechanical removal, forage plants become more fibrous and lignify, decreasing feed value. Low-quality forages cannot satisfy energy requirements of lactating dairy cows. Therefore, it is imperative to develop management decision guidelines to increase the bio-economic efficiency and forage utilization without causing detrimental effects to soil conditions.

Management practices

Various management practices can improve soil health. Subsurface drainage systems, like tile drainage, can help remove excess water from land. It may be worth tiling poorly drained fields to improve infiltration.

Water infiltration in compacted soils can be increased through mechanical aeration as well. However, economic and practical aspects need to be considered, particularly for humid environments, where many soils are prone to soil compaction and waterlogging. Using machinery on wet soils can be even more damaging than livestock.

Flash (on/off) grazing

Adaptive grazing management practices should be used when the temperature enables pasture growth but soil conditions are susceptible to trampling damage due to high moisture content. A typical management system for dairy cows consists of animals being confined during the cool, wet season. This may lead to low pasture utilization and to accumulation of more stemmy forages in the late spring/summer period, resulting in poor-quality pastures.

On-off (flash) grazing is a management practice that can reduce damage to soil and pasture when grazing wet paddocks. In on-off grazing management, livestock are turned onto pasture paddocks to graze for a short period of time (less than four hours). Then animals are moved to a sacrifice paddock or onto a paved or gravel area where they are fed supplemental forage.

Grazing with light stock

Pasture utilization and forage quality can be improved without damaging the physical and structural conditions of seasonally wet soils through adaptive management practices that employ grazing with lightweight stock. Often, grazing wet pastures with sheep or heifers is a valuable practice to prevent the buildup of excess low-quality forage without causing excessive pugging.

Choice of a pasture mixture for poorly drained paddocks

The response and resilience of pasture species and mixture combinations to animal traffic differs. Certain forage species are more sensitive to trampling and stage of maturity when they are subjected to heavy livestock traffic. Sod-forming grasses that produce rhizomes or stolons can tolerate trampling in wet conditions better than those bunchgrasses with tufted growth habit.

Traditionally, grazing-based dairies rely primarily on perennial ryegrass and white clover pastures. This pasture combination provides an abundance of high-quality feed in spring and is more tolerant of trampling than orchardgrass or red clover. An alternative to grass-clover pastures in problematic soils can be designing specialized pastures through using more summer-active pasture species like legumes and herbs.

Due to their higher temperature requirements, legume species have slower growth rates in early spring. They provide high-quality forage in late spring and summer when the growth rates and quality of grasses decrease. A significant distinction between grasses and legumes is: Reduction in feeding values of legumes with maturation is less profound than grasses. Pasture herbs like chicory also have the highest amount of digestible forage in the summer and fall compared to grass-clover pasture mixes. Therefore, try diversifying pastures through using well-managed, specialized forb- and legume-based pastures that are better able to maintain their growth rates and feeding quality toward summer and provide superior animal performance.

In particular, birdsfoot trefoil (Lotus corniculatus L.) is highly tolerant of both waterlogging and summer dry conditions. In addition, it contains highly active condensed tannins and requires less lime than white clover for nodulation in acid soils. However, birdsfoot trefoil is slow to establish and not highly competitive with fast-growing species. Therefore, combining birdsfoot trefoil with other waterlogging-tolerant annual legumes such as balansa clover (Trifolium michelianum Savi) or Persian (reversed) clover (Trifolium resupinatum L.) may help increase the first-year production of the pasture stands.

Overseeding deep-rooted annual crops to improve infiltration

Vegetation can help improve soil aeration and infiltration by providing root channels that enable the flow of water and air. Yet the sown grass-clover combinations traditionally used in grazing pastures have shallow rooting systems that are often ineffective in promoting soil aeration and water transport. Variable rooting structure plant mixtures can be used as biological tools to improve soil aeration, carbon sequestration and water transport through the soil profile.

A novel and practical strategy to enhance soil health is through overseeding herbs and brassicas with deep tap roots into existing grass-dominated pastures. Deep-rooted plants form deep channels in soil that enable greater infiltration, reducing surface runoff. They also better utilize nutrients and water, reducing nitrate leaching below the rooting zone. For instance, brassica species like forage radish (Raphanus sativus L.) may improve N utilization due to more effective scavenging of mineral N and help aeration of soils during winter when other plants are dormant.

Additional benefits of diversifying species composition in grazing pastures include enhancing ecosystem services such as carbon sequestration, water quality and habitat for bee pollinator species. Adding brassica and legume species in pasture mixtures also helps large-scale promotion of honeybees and native bee species.  end mark

David Hannaway is a professor with the department of crop and soil science, Oregon State University.

Serkan Ates is with the Department of Animal and Rangeland Sciences at Oregon State University. Email Serkan Ates.

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