Enhancing Climate Resilience of Forage Ecosystems Through Sustainable Intensification and Educational Knowledge Transfer in the Southeastern USA

Abstract

Forages are the primary feed source for livestock production systems due to their diversity of adapted species and lower production costs. Forage-based livestock operations are complex systems across climates, soil types, genetics, and production systems. Therefore, increasing the resilience of forage ecosystems requires a comprehensive approach to assess and understand the conditions of each system while considering its needs, goals, and resources. In the southeastern USA, favorable climatic conditions allow for the incorporation of annual forage species into perennial stands to extend the grazing season. Adopting management strategies that support forage biodiversity and nutrients, and land use efficiency are ways to improve sustainable production intensification of forage ecosystems. Additionally, providing proper access to education and knowledge transfer for current and future generations is essential to guarantee the success and longevity of the livestock industry. This review provides an overview of key issues related to the climate and economic resilience of forage–livestock ecosystems and the role of agricultural education and knowledge transfer in shaping sustainable ecosystems.

1. Introduction

Grasslands occupy one-third of the total agricultural land area in the United States of America (USA) [1]. Although grasslands play a critical role in the livestock industry as the primary source of feed for animals [2], they are traditionally sites with low agricultural suitability and primarily under non-irrigated conditions. With the growing world population and limited areas for agricultural expansion, the agricultural sector faces challenges to increase food and fiber production while minimizing negative impacts on the environment. Ruminants can convert high fiber products and coproducts (e.g., sugarcane bagasse, cottonseed) into protein-dense animal products for human consumption [3]. Additionally, grasslands deliver a wide range of ecosystem services (ES), supporting the sustainability of the ecosystems [4]. In this context, using sustainable intensification strategies enhances production per area, resiliency, and economic viability of operations.

Climate change is defined as changes that persist for decades and are expected to impact, directly or indirectly, food security and agricultural production [5]. Future climate scenario simulations show changes in rainfall and temperature patterns in the world’s main agricultural regions [6]. Hence, these changes may impact forage systems, such as decreased productivity and nutritive value and increased seasonality [7,8]. Anthropogenic activities are the main drivers of climate change, primarily due to greenhouse gas (GHG) emissions. Currently, the carbon dioxide (CO₂) atmospheric concentration is estimated at ~422 µL CO₂ L⁻¹, but it is expected to reach between 450 and 520 µL CO₂ L⁻¹ by 2040 [9]. The increase in the CO₂ atmospheric concentration may impact forage production and the nutritive value of C3 and C4 species [9,10,11,12,13], as well as the overall system environment.

Over recent decades, there has been an emphasis on reducing the negative impacts while enhancing the positive environmental benefits from forage–livestock systems [14], which has directly informed forage science research initiatives and educational efforts. In the southeastern USA region, the majority of livestock producers are classified as small farmers [15]. In this context, production costs, management strategies, and innovative technologies must meet their needs and be feasible to allow for the longevity of these operations in the livestock industry. There is a growing need to advance educational aspects and transfer knowledge about sustainable food production to farmers and the general population. This review focuses on strategies to enhance the climate and economic resilience of forage–livestock ecosystems and the role of agricultural education and knowledge transfer in shaping future generations and sustainable ecosystems.

2. Forage–Livestock Operations in the Southeastern USA

The southeastern USA region encompasses twelve states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, and Texas) [16]. This region’s climatic conditions are characterized as humid subtropical, with hot, humid summers and mild, wet winters [17]. The livestock industry is one of the most important agricultural activities in the Southeast, and cow–calf operations are predominant, with over 12 million beef calves [15]. The livestock operations are primarily based on perennial grasses such as bahiagrass (Paspalum notatum Flueggé), bermudagrass (Cynodon dactylon L.), and tall fescue (Festuca arundinaceae (Schreb.) Dumort.). These perennial grasses require inorganic nitrogen (N) fertilizer to support forage production and nutritive value to sustain animal performance [18], which contributes to increasing the environmental footprint of the livestock industry.

The seasonality of forage production of perennial grasses is a major challenge for livestock operations. This requires the use of conserved feed (e.g., hay), supplements, and the use of annual cool- and warm-season forages to meet the forage needs for the livestock herd. The costs related to livestock feeding during the fall and winter months can represent over 40% of annual operating costs [19]. Therefore, increasing interest has been in using annual forages to extend the grazing season. The most used annual cool-season forages are cereal ryegrass (Secale cereale L.), oat (Avena sativa L.), wheat (Triticum sativum), annual ryegrass (Lolium multiflorum), and clovers (Trifolium spp.) [17]. Mixing these forage species to combine forage growth distributions and maturities to extend the grazing season length has been widely adopted by operations [20]. For warm-season annuals, the most used species are pearl millet (Pennisetum glaucum), sorghum (Sorghum bicolor L.), sorghum–sudangrass (Sorghum bicolor L. × S. arundinaceous hybrid), crabgrass (Digitaria sanguinalis), cowpea (Vigna unguiculata) [21], and sunn hemp (Crotalaria juncea). These are high-production and nutritive value forages that grow during the warmer months and complement the nutritional requirements of livestock [22].

3. Climate-Resilient Sustainable Intensification Strategies for Forage Ecosystems

The Food and Agriculture Organization (FAO) of the United Nations defines sustainable food systems as those that “deliver food security and nutrition for all in such a way that the economic, social, and environmental bases to generate food security and nutrition for future generations are preserved” [23]. Over the past decades, there has been an increasing focus on better understanding nutrient accumulation and resilience responses to management practices that support grassland productivity, ecosystem services, and the mitigation of greenhouse gases [24,25,26]. In this context, climate-resilient management strategies (CRMS) are gaining more emphasis, since they are improved strategies that support forage production, nutrient cycling and accumulation, and soil organic carbon (SOC) and stability [27,28,29,30,31,32]. The CRMS requires an integrated approach to addressing plant, animal, human, and environmental factors, and their interrelationships, and contributes to sustainable, ecological, and economically resilient operations. This review will focus on three major CRMS and briefly describe and discuss how they can support grassland ecosystems in the scope of climate change in the southeastern USA.

3.1. The Use of Diverse Forage Mixtures

Diversified agricultural systems can improve the agronomic and ecological responses of ecosystems [33] and complement forage production, distribution, and nutritive value through the proper combination of different plant functional groups (e.g., grass, legume, brassica) in livestock operations. In the Southeast, a common practice is to overseed perennial grass stands (e.g., bermudagrass, bahiagrass) with cool-season annuals to extend the grazing season [17]. Traditionally, these overseeded systems are based on a small grain monoculture or combination with annual ryegrass, with multiple studies conducted to assess and summarize agronomic and animal performance responses [17,34,35,36,37,38]. In Marianna, FL, a 2-year study investigated the animal performance and production characteristics of three binary cool-season annual mixtures (ryegrass–annual ryegrass, oat–annual ryegrass, and triticale–annual ryegrass) [37]. These mixtures were sown into a prepared seedbed, and the authors reported an average daily gain (ADG) of 0.85 to 0.90 kg head⁻¹ d⁻¹ for Angus steers grazing. In addition, the authors mentioned that oat and triticale demonstrated a more even distribution of growth rates during the season, which allowed for better adjustments to stocking rates and grazing management.

Forage legumes (e.g., clovers) can add organic N into the system through the biological nitrogen fixation BNF [39], and their incorporation is the most common practice when diversifying grass-based forage systems [17,37,40,41,42,43]. In recent decades, there has been growing interest in their incorporation due to their ability to conduct BNF [39], reduce GHG emissions, improve forage and animal performance [38,44,45,46,47,48], and support nutrient cycling [49,50,51], pollinators’ habitat [52], and SOC accumulation [27,53]. Additional ecosystem services and environmental benefits of forage legumes and their incorporation into forage systems have been described in previous studies [26,54,55]. In a 2-year study conducted in Florida, bahiagrass stands were managed either in monoculture (with or without N fertilizer) or in a mixture with rhizoma perennial peanut (Arachis glabrata L.) [46]. These forage systems were overseeded in fall with cool-season annual mixtures [grass only (oat–ryegrass) or grass–clovers]. The authors reported similar average daily gains and stocking rates for the winter period across treatments (0.87 kg⁻¹ d⁻¹ and 2.7 animal unit (AU) ha⁻¹, respectively). A 2-year study [56] determined agronomic, litter decomposition, and soil nutrient accumulation responses in year-round N-fertilized grass [bermudagrass and ryegrass–annual ryegrass; 290 kg N ha⁻¹ yr⁻¹] and legume–grass [rhizome perennial peanut–annual ryegrass–clovers (crimson and red); 30 kg N ha⁻¹ yr⁻¹] systems under two defoliation methods [grazing and mechanical harvest (hay)]. The authors reported greater annual herbage accumulation for N-fertilized grass over the legume–grass system under grazing and hay management (9680 and 10,100 kg DM ha⁻¹ vs. 5900 and 5690 kg DM ha⁻¹, respectively). In this study, the greater annual herbage and nutrient accumulation observed was associated with a larger environmental footprint and economic costs.

Brassicas are high-nutritive value and production forage crops [57] that can scavenge for nutrients and improve water infiltration and soil structure, while adding organic matter (OM), in deeper soil profiles. In a 2-year study, the authors determined agronomic responses of seven cool-season annual forages in monoculture and a three-way mixture (radish–grass–clover) in Louisiana [58]. A 2-year study conducted in Kansas evaluated the forage mass, plant composition, and costs of three-way cover crop mixtures planted in August [59]. The authors reported that grasses and brassicas contributed to a greater portion of the mixtures and that mixing different plant functional groups was the most economical forage option. There is still limited information for determining the fitness of diverse plant functional groups in forage mixtures under grazing in the southeastern region and for optimizing agronomic and environmental responses while reducing the costs of dry matter production in operations.

Another system that has been expanding in adoption is alfalfa–bermudagrass systems (ABG), as producers are aiming to improve forage production and nutritive value while reducing inorganic N input into grass fields [60,61,62,63]. The adoption of alfalfa in the southeastern region has been possible through breeding efforts that developed grazing-tolerant, dual-purpose cultivars, allowing management through grazing or conserved forage production [64,65]. Under conserved forage production, the authors reported higher forage mass, nutritive value, and a longer production season for ABG versus bermudagrass monocultures [62]. Previous studies determined the plant and animal responses of ABG under grazing management, including undercut-grazing and stockpiling strategies, in an attempt to better determine grazing management, production distribution and length, and strategies to optimize agronomic, animal, and ecological responses [60,61,66]. A 2-year study was conducted at Headland, AL, and Tifton, GA, to determine the forage and animal responses of ABG managed undercut only (baleage production), graze only, and cut–graze strategies [66]. The authors reported crude protein ranging from 15% to 22% for the treatments and animal unit days from 178 to 322.

3.2. The Use of Integrated Systems in Livestock Operations

The use of integrated systems has been increasing over the past decades, aiming to optimize resource use efficiency, productivity, and ecosystem services, and diversifying operational income [33,67,68,69]. Diversified agricultural systems improve ecological responses by enhancing nutrient cycling, soil health, and biodiversity while supporting control of weeds, insects, and diseases [33]. There are several variations in the integration of plant crops (e.g., row crops, trees) and livestock in single integrated systems used worldwide. The integrated crop–livestock system (ICLS) is an approach that has been used worldwide since the 20th century and continues to expand in the southeastern region [33,68,70]. On ICLS, cover crops (e.g., cereal ryegrass) are planted in row crops (e.g., cotton (Gossypium hirsutum L.)) areas during their off-season and grazed by livestock. Cover crops are defined as grasses, legumes, and forbs, and they are used for improving soil structure, fertility, and microbiota diversity, reducing leaching and runoff, and weed suppression, among other benefits [71]. A 3-year study determined the short-term effects of cover crop planting in contrasting cropping systems, including ICLS, imposing different grazing intensities and N fertilization strategies [71]. The authors reported that cover crops decreased cumulative N leaching compared to fallow areas (18 vs. 32 kg N ha⁻¹ season⁻¹). In a review of ICLS fitness to support agricultural resilience to climate change, the authors concluded that ICLS can support agroecosystems’ long-term stability and economic and ecological benefits. However, this will require properly incorporating environmental knowledge into management strategies [72].

Silvopasture integrates trees, forages, and livestock into a single production system [73]. Due to the reduction of solar radiation available for the forage canopy, there may be a reduction in forage production in these systems [74,75]. However, silvopasture provides thermal comfort for livestock grazing [76], which reflects in animal performance and reproductive parameters [77,78] and ecosystem services, such as nutrient cycling, soil health, and water infiltration and quality. In a review of the impact of silvopasture in the southeastern USA region, the authors reported multiple ecosystem services and benefits for silvopasture use and emphasized the need for further investigation in long-term field experiments to better understand responses and variations due to edaphoclimatic characteristics [79]. Silvopasture is a viable alternative for sustainable intensification within the scope of climate change [76], due to enhanced efficiency in the use of resources and productivity [80], while collaborating in the reduction of GHG emissions [81].

3.3. Soil Fertility, Health, and Nutrient Accumulation

Soil is a complex system [82] that is crucial for food production and the sustainability and delivery of environmental benefits by agricultural ecosystems [83]. Soil health is defined as the capacity of soil to continue to function as a living ecosystem that sustains plants, animals, and human beings [84] and encompasses biological, chemical, and physical parameters. Soil health includes effects on water quality, plant, and animal health within the ecosystem [85] and management practices (e.g., tillage, plant biodiversity) applied to the forage system to directly impact it and its fauna communities. Biodiversity in forage systems offers contrasting phenology to support beneficial insects (e.g., pollinators, dung beetles) and microbial communities.

Nutrient cycling is crucial to support soil fertility and overall ecosystem sustainability. In grazing systems, dung beetles play an essential role in the incorporation and decomposition of dung, as coprophagous insects, and nutrient release [N, phosphorus (P), and potassium (K)] [86]. They are classified as dwellers, rollers, and tunnellers based on their nesting techniques [87]. Dung beetles also support soil characteristics and health through improved water infiltration and porosity [87], bulk density reduction, and microbiota diversity [87,88] and can also influence GHG, especially for nitrous oxide [89]. A study was conducted in Marianna, FL, using contrasting systems to determine the role of dung beetle species on nitrous oxide emissions, ammonia volatilization, and nutrient cycling [89]. The authors reported that the dung beetles, Onthophagus taurus and Digitonthophagus gazella, were associated with improved N mineralization, enhancing plant uptake. The ecological benefits of dung beetles extend to enhanced plant health; therefore, correctly understanding sustainable management practices to improve soil nutrient and dung beetle interactions in forage systems is crucial. Similarly, pollinators’ presence enhances wildlife diversity; beneficial insects help to control pests and are associated with higher-quality seeds (for reseeding pastures). Biodiversity is crucial to extend the feed availability for pollinators, and the presence of native plant species can support native pollinator communities and is currently of elevated importance, especially for bees.

Grasslands occupy an estimated 3.5 billion ha globally, and due to the reduced disturbance and frequent input of above- and belowground plant biomass, soils under perennial stands are important C sinks [27,28,90]. Management practices that cause soil disturbance (e.g., disking, tillage) impact soil organic carbon (SOC) accumulation and stability in the soil. In a review of 126 studies, [27] observed rates of soil organic carbon accumulation of 0.82 and 0.54 Mg C ha⁻¹ yr⁻¹ under organic and inorganic fertilizer application, respectively. Studies have shown a positive effect of legume and legume–grass systems over grass-only systems in soil C accumulation [56,91,92]. However, these results are not guaranteed, as reported by [93], who evaluated the changes in C and N accumulation in the soil after six years in a grass system with high N fertilizer input versus a legume-based system. They observed greater changes in N in the soil surface under the N-fertilized grass system. They concluded that further research is necessary to better understand the main drivers of nutrient accumulation and how forage functional groups and fertilization management impact forage systems.

3.4. Strategies for Greenhouse Gas Emissions Mitigation in Forage–Livestock Systems

In recent decades, there has been increasing emphasis on the implementation of sustainable livestock production to reduce their carbon footprint and GHG emissions while supporting the production, animal performance, and feasibility of operations [94]. Livestock activities emitted around 18% of global non-CO₂ GHG emissions [94]. Ongoing research efforts aim to develop strategies to mitigate enteric methane (CH₄) and nitrous oxide (N₂O) emissions since they are the major GHGs associated with livestock production systems. The primary emissions of CH₄ are enteric fermentation [95], and of N₂O are animal excreta (i.e., urine), decomposition, and inorganic fertilizer use [96]. Research efforts have focused on developing management practices and novel products (e.g., additives) that support the reduction of GHG emissions in forage–livestock systems. For example, incorporating legumes into forage systems has been seen as an option to reduce the use of inorganic N fertilizers and reduce the carbon footprint of the activity [97]. Although cumulative N₂O emissions from legume systems can be similar to N-fertilized grass systems, the soil losses were less in the legume systems, while [48] reported GHG emissions reductions from beef steer excreta under tannin-rich forage legume diets.

Methane production is a natural process in ruminants [98]. Among the strategies to mitigate CH₄ emissions are selecting animals with improved feed conversion, use of additives, and enhanced diet digestibility [98,99,100]. Ruminants fed legume-containing diets tend to emit less enteric CH₄ [99,100] due to grass monocultures’ increased forage nutritive value. A meat analysis [99] showed 17% higher CH₄ emission (per kg intake) for ruminants consuming C₄ than C₃ grasses. Over the past decades, there has been growing research interest in using condensed tannins in ruminant diets as natural mediators of rumen fermentation [48,100]. Condensed tannins are plant secondary metabolites, and their concentration varies widely. Among the rich condensed tanning forage species, sericea lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don.] has been a research focus for different animal species. Regarding grazing management, improved practices that improve forage nutritive value, reduce plant maturity, and balance the spatial nutrient distribution can mitigate CH₄ emissions. There has been an increase in the development of comprehensive life cycle assessments for forage–livestock systems. Still, further investigation and funding acquisition are needed, since these efforts are costly and labor-intensive.

There is limited GHG emissions information about pasture-based livestock systems, including commercial beef operations. While discussing some of the challenges associated with conducting grazing research, Sollenberger [14] mentioned limited spatial and time scales, constraints to measuring key variables, and the scarcity of funding. Similarly, ongoing studies in the southeastern region estimating GHG responses (personal communication) face limitations, including the prohibitive cost of equipment and personnel required, infrastructure, and limited funding opportunities to maintain long-term, year-round studies, limiting the ability to acquire “real-world” estimates. Additionally, the availability of livestock, overhead costs, and limited funding availability to apply for within the specific scope of work have been constant challenges faced by researchers in the forage and pasture science area for decades. Additionally, new CRMS need to be practical, scalable, and financially sound to facilitate and encourage adoption by farmers. Practices that promote year-round grazing, improve soil fertility and health, and carbon accumulation are viable options. Still, producers need to properly understand their management principles and goals for implementation into their operations. Therefore, agricultural education and knowledge transfer are key factors in this process and are underestimated, as educators and researchers are responsible for bridging the gap between innovation and on-farm adoption.

4. The Role of Agricultural Education and Knowledge Transfer in Shaping Climate-Resilient Forage–Livestock Ecosystems

Higher education institutions (HEIs) are crucial in developing innovative knowledge and technologies while providing expertise and practical experience transfer through proper educational efforts for current and future farmers to adopt into their operations. Bridging the gap between developed research and practical application requires the development of multi-format educational resources and the understanding that operations have specific needs, goals and resource availability [101], which requires a holistic analysis to best address issues and provide proper recommendations for adoption by farmers [102,103]. In this context, the availability of well-trained educators is crucial, and these educators need to be able to establish collaborative interactions with stakeholders, communities, and organizations to reach and impact farmers adequately [104]. Agunbiade et al. [79] emphasized the role that the extension services play in transferring the scientific findings into educational resources and technical support to producers. Similarly, Silva et al. [104] concluded that educational resources and training are needed to support farmers in making educated management and economic decisions and better understanding the ecological responses of forage ecosystems in the southern USA.

In the current scenario, livestock production systems must identify improved management strategies to reduce feed costs and off-farm inputs while supporting operations’ sustainability, resilience, and feasibility [4,52,105]. However, there are limitations regarding farmers’ perceptions and access to research-based information and cost-share programs that can limit their ability to innovate and adapt in their operations. Multi-state collaborations through HEIs initiatives are increasing to address common issues and improve engagement and reach of farmers and communities, including beginner farmers [106]. Additionally, educating the public and consumers is necessary since a wide range of misinformation is available about agriculture and production systems. Consumer perceptions about agriculture, food production, and environmental impacts have been central to discussions over the last decades [107]. However, there is a significant disconnect between the public and food production systems; therefore, farmers face substantial challenges in enhancing sustainable production while remaining profitable in the livestock industry. Hence, there is an enhanced emphasis on teaching and engaging the youth in agriculture, aiming to repair the disconnect between food systems and the public and support their involvement in the livestock industry. In the southeast, most farmers are considered small [15], and optimizing their access to technical information enhances resource use efficiency, supporting their continuity in the livestock business.

5. Conclusions and Implications

With the growing world population, the agricultural industry faces challenges to enhance production to meet food demands, especially in the face of climate change and its impacts, such as increased temperatures and changes to rainfall patterns. Well-managed grasslands play a key role in supplying high-protein animal sources, contributing to land use efficiency and conservation and delivering ecosystem services. Over the past decades, there has been a growing emphasis on forage research efforts in developing and implementing CRMS in grasslands to cope with impacts from changing climate conditions. Among the CRMS, the increasing plant diversity in forage ecosystems has been expanding because the combination of species allows for improved forage growth, distribution, and nutritive value. Thus, when utilizing forage legumes, there is the added benefit of the input of organic N into soil, enhancing soil fertility and health over time, and supporting organic matter and carbon accumulation and stability. Strategies that optimize nutrient distribution and cycling in systems are essential to allow for adequate use of resources while reducing runoff and leaching that could lead to environmental issues.

Additionally, using contrasting plant groups to optimize species diversity supports improved nutrient recycling, soil characteristics optimization, and soil macro- and micro-biota. In ICLS, the presence of livestock grazing areas intensifies the nutrient deposition and cycling, while also helping reduce some off-farm inputs, such as herbicides, since using cover crops helps with weed suppression. In silvopasture, there is an increase in land use efficiency while supporting animal welfare and income diversification, which is particularly important for small producers. Due to their importance and role in supporting resilient systems, a proper understanding of OM and SOC deposition and accumulation, and strategies to reduce GHG emissions are currently among the most essential topics in research efforts. However, there are still challenges with funding scarcity to support infrastructure, equipment, and personnel needed to conduct grazing studies to properly determine key variables related to those responses and conduct long-term studies.

Some efforts aim to build sustainability-related markets for additional gains for forage and livestock producers, such as carbon credits. Unfortunately, there is still a need for a better understanding and more scientific information to guide proper predictions of long-term estimates of carbon accumulation in various edaphoclimatic conditions and grassland management strategies. Large regional multidisciplinary funding initiatives that are interdisciplinary in measuring soil nutrient accumulation are a good example of ways to generate the data needed to inform and build future carbon credit markets. In addition to the marketing and economic aspects, the role of education in bridging the gap between scientific findings and the implementation of technologies must be appropriately addressed by agricultural educators and researchers. The transference of CRMS research-based findings requires multi-format educational resources, and the involvement with practical on-farm demonstration is a valid way to support the adoption of practices while reaching wider groups and communities, including youth. The CRMS supports enhanced productivity and ecological and economic resilience, but these solutions must be practical, scalable, and financially sound for farmers to adopt.