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Ecosystem services of grass- and legume-based year-round forage systems managed under grazing or hay harvest
Abstract
Link for download: https://ufdc.ufl.edu/UFE0056041/00001
Perennial grasses are the predominant feed source for ruminant livestock in Florida, but N fertilizer is required to maintain acceptable levels of forage productivity, persistence, and nutritive value. Use of N fertilizer may increase greenhouse gas (GHG) emissions
and risk of nitrate leaching to groundwater, and it may not be economical in some situations. Legumes are an alternative to N fertilizer to potentially address these limitations. The objective of this research was to compare the effects of year-round N fertilized grass (GN)- and legume (LG)-based forage systems, defoliated by grazing or
cutting for hay on nutrient cycling in plant litter, emissions of nitrous oxide (N2O), and accumulation of soil carbon (C) and nitrogen (N). Greater herbage accumulation of GN than LG systems resulted in greater existing litter mass for GN. The LG system released 60% as much N as GN over two years (36 vs 59 kg N), despite receiving only
10% (30 vs. 290 kg N ha-1 yr-1) as much N fertilizer as GN. Thus, LG systems contributed important quantities of N through decomposition of aboveground plant litter, potentially decreasing need for N fertilizer. Nitrous oxide emissions varied widely among seasons and within and among treatments. The greatest emissions were associated with the GN treatment in summer and occurrence of significant rainfall events. The greatest N2O emissions following N fertilization of GN systems occurred by 20 d after fertilization. Differences among systems in cumulative emissions were observed only in summer of Year 2 when emissions for GN were approximately four times as great as for
LG. Cumulative changes in soil C stock to a 0- to 20-cm depth averaged 2.6 and 0.32 Mg C ha-1 year-1for GN and LG systems, respectively, while N accumulation averaged 0.3 and 0.2 Mg ha-1 year-1, respectively, and was 4.5 times greater for grazed than hayed LG treatments. The LG systems provided less but important amounts of N through plant litter, had lesser N2O emissions, and amounts of soil C and N accumulation than GN systems, while receiving only 10% as much N fertilizer year-1 as GN systems.
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The ingrowth core method for measuring root accumulation has several advantages over sequential soil cores or mini‐rhizotrons. However, current ingrowth core designs are not well suited for use with rhizomatous perennial forage species or when defoliation occurs during the measurement period. Our objective was to develop a modified ingrowth core device and to evaluate its use for measuring root‐rhizome accumulation of a rhizomatous perennial forage in a hay management context. The modified ingrowth cores were constructed of 4‐mm polyester mesh surrounding a 7.5‐cm diameter cylinder constructed of cage wire. Field testing of the core design involved placing three ingrowth cores in each of four replicates of six treatments arranged in a randomized complete block design. Treatments consisted of six rhizoma peanut (Arachis glabrata Benth.) entries, and they were evaluated during 2017 and 2018. The ingrowth core design facilitated ease of placement, maintenance of core structural integrity throughout 100‐d deployment periods, rapid location of cores using a metal detector at the end of deployment periods, and precision to detect differences among treatments. We conclude that this modified ingrowth core design is well suited for measuring root‐rhizome accumulation rate of perennial forage species.
Core Ideas Root or root‐rhizome biomass is the dominant C supply to grassland soils.
There is little information on root‐rhizome accumulation rates under perennial forage crops.
A modified root ingrowth core device was developed and tested in a field study.
The modified core maintained structural integrity and successfully detected differences among treatments.
Core Ideas
Bahiagrass–rhizoma peanut mixtures resulted in similar whole soil C stocks as N‐fertilized bahiagrass monocultures.
Bahiagrass–rhizoma peanut mixtures had greater total and particulate organic matter C than rhizoma peanut monocultures.
Particulate organic matter C/N ratio of rhizoma peanut and N‐fertilized bahiagrass monocultures were lower than C/N ratio in bahiagrass–rhizoma peanut mixtures.
The use of δ¹³C to verify changes in the soil organic matter caused by the plant component was a better predictor than the use of δ¹⁵N.
Soil particulate organic matter (POM) represents a labile soil organic matter (SOM) fraction and is an important source of nutrients for soil microorganisms and plants. This study assessed C and N stocks in POM and soil mineral‐associated fractions for forage mixtures of rhizoma peanut (RP; Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flüggé) in contrast with their monocultures. Treatments included two bahiagrass entries receiving 90 kg N ha–1 harvest–1, two RP entries, and the four bahiagrass–RP combinations. Samples were collected from the 0‐ to 15‐cm soil depth in July 2015 and in September 2016, after seven harvests. Soil samples were fractionated into POM and mineral‐associated organic matter (MAOM) by dispersion with sodium hexametaphosphate and sieving (53 μm). Samples were analyzed for δ¹³C, δ¹⁵N, and total C and N. Groups of bahiagrass, bahiagrass–RP, and RP were contrasted. There were no differences in N stocks among forage treatments. Bahiagrass–RP mixtures had greater soil POM‐C stock (5.1 Mg C ha–1) than RP monocultures (4.0 Mg C ha–1). Soil POM C/N ratio was lower for bahiagrass (18.2) and RP monocultures (16.2) than bahiagrass–RP (20.6). Bahiagrass–RP and bahiagrass had similar soil δ¹³C and were less depleted than RP (–23‰ vs. –26‰ and –26‰ vs. –28‰, for POM and MAOM, respectively). Soil POM‐C stock under forage mixtures was not different from N‐fertilized bahiagrass, and it was greater than RP. Hence, mixing RP and bahiagrass can be an option to increase POM‐C without the need of N fertilizer.
Ecosystem services (ES) are the direct and indirect contributions of ecosystems to human well‐being. Grassland ecosystems cover >40% of Earth's ice‐free terrestrial surface, and grassland management affects the ES provided. Our objective was to synthesize the existing literature assessing management effects on regulating and supporting ES provided by grasslands, explore the related mechanisms, and determine which practices favor ES delivery. Current literature supports the following conclusions. Increasing management intensity of grasslands through planting more productive species or increasing fertilizer inputs generally increases soil organic C (SOC) accumulation. Increasing the number of plant species or functional groups, especially when legumes are added, often increases SOC accumulation. Grazed grasslands generally accumulate SOC more rapidly than undefoliated grasslands. Low or moderate stocking rates favor SOC accumulation relative to high stocking rates, especially in lower‐rainfall environments. Short‐term SOC accumulation rates observed after conversion of cropland to perennial grassland do not continue indefinitely. More digestible forages defoliated at optimal maturity may decrease CH4 emitted per unit of feed consumed or per unit of animal product. Substituting legumes for N fertilizer and reducing livestock N excretion through diet manipulation reduce N2O emissions. Managing grazing to increase uniformity of excreta deposition increases efficiency of nutrient cycling. Species‐rich grasslands with flower‐rich legumes and forbs increase foraging opportunities for pollinators. Finally, to optimize delivery of grassland ES, management practices that sustain ecosystem function likely need to replace those that maximize short‐term resource utilization or economic return. To encourage adoption, such practices may need to be incentivized.
Soil organic carbon (SOC) is primarily formed from plant inputs, but the relative carbon (C) contributions from living root inputs (i.e. rhizodeposits) vs litter inputs (i.e. root + shoot litter) are poorly understood. Recent theory suggests that living root inputs exert a disproportionate influence on SOC formation, but few field studies have explicitly tested this by separately tracking living root vs litter inputs as they move through the soil food web and into distinct SOC pools.
We used a manipulative field experiment with an annual C4 grass in a forest understory to differentially track its living root vs litter inputs into the soil and to assess net SOC formation over multiple years.
We show that living root inputs are 2–13 times more efficient than litter inputs in forming both slow‐cycling, mineral‐associated SOC as well as fast‐cycling, particulate organic C. Furthermore, we demonstrate that living root inputs are more efficiently anabolized by the soil microbial community en route to the mineral‐associated SOC pool (dubbed ‘the in vivo microbial turnover pathway’).
Overall, our findings provide support for the primacy of living root inputs in forming SOC. However, we also highlight the possibility of nonadditive effects of living root and litter inputs, which may deplete SOC pools despite greater SOC formation rates.
Overseeding warm-season legumes into warm-season perennial grass pastures may increase productivity and nutritive value of pastures in tropical and subtropical regions. The objective of this study was to investigate the effects of overseeding ‘Amarillo’ pintoi peanut (Arachis pintoi Krapov. & W.C. Greg.) into Jiggs bermudagrass [Cynodon dactylon (L.) Pers.] pastures grazed at different stubble heights. The experiment was conducted in Ona, FL, from June to October in 2014 and 2015. Treatments were a split-plot design of two sward types (bermu-dagrass monocultures or overseeded with pintoi peanut, main plots) and two postgrazing stubble heights (15 or 25 cm [SH15 and SH25], subplots) arranged in a randomized complete block design with four replicates. Pastures were mob stocked, with 28-d resting periods between grazing events. There was no effect of stubble height on pintoi peanut plant density (5.8 plants m⁻²), ground cover (5.8%), or proportion in the herbage mass (HM, 5.2%); however, proportion in the HM increased from 1.1 to 8.2% over 2 yr. There was no effect of sward type on weed ground cover; however, SH25 had greater weed ground cover than SH15 (53.4 vs. 18.2%). Herbage accumulation rate, crude protein, and in vitro digestible organic matter were not affected by sward type (23.4 kg ha⁻¹ d⁻¹, 101 g kg⁻¹, and 431 g kg⁻¹, respectively). Pintoi peanut proportion in the HM increased over time; however, it may take >2 yr to have a significant presence of pintoi peanut in the mixed sward. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Soil organic carbon (SOC) plays a critical role in the sustainability of grazingland ecosystems around the world. However, maintaining or increasing SOC levels remains a major challenge, particularly in subtropical regions where coarse-textured soils predominate. This study evaluated the long-term (>20 years) impacts of grazingland intensification (conversion of native rangelands into more intensively managed silvopasture and sown pasture) on SOC and nitrogen (N) responses in particle size/density fractions. Treatments consisted of field replicated (n = 2) experimental sites that represented a gradient of intensification ranging from native rangelands (low intensification), pine (Pinus spp.)-bahiagrass (Paspalum notatum) silvopasture (moderate intensification), and bahiagrass pastures (high intensification). Soil organic C and N increased in response to the conversion of native rangelands into more intensively managed grazinglands, but no difference was observed in total SOC and N between silvopasture and sown pasture. Despite the positive impact of intensification on SOC and N pools, accumulation occurred primarily in more labile fractions. For instance, at the 0 to 10 cm depth, light-free C (LF-C) increased from 12.9 g kg⁻¹ soil in the native rangeland to 24.7 g kg⁻¹ soil in the sown pasture. Largest differences between the ecosystems were observed at the 10 to 20 cm depth where LF-C increased by as much as 170% following the conversion from native rangelands to sown pasture. Similar responses were also observed for N. Grazingland intensification showed no effect on soil aggregation, but SOC and N associated with macroaggregates (2,000 to 250 μm) increased with intensification. Results indicate that grazingland intensification promoted SOC and N accumulation, primarily through an increase in the LF fraction. © 2018 Soil Conservation Society of America. All rights reserved.
Southern cow-calf producers are expected to experience multiple years of tight margins and cash flow constraints due to cattle market prices adjusting to price levels below the average cost of production. To combat this, a team of Extension specialists from across the Southeast United States began working on areas to reduce cow-calf cost of production. One critical area the team chose to address was the cost of wintering the cowherd. Producers usually feed hay, stored feedstuffs, stockpiled forage, cool-season annual forage, and other supplements once warm-season perennial grasses become dormant. Feeding during this time period could last for 90 to 180 d based on management programs and weather conditions. Regardless, most cow-calf producers will agree this is a very costly activity and greatly reduces the profitability of their operation. During the fall of 2016 and 2017, six Extension programs were held to discuss the current winter forage situation and evaluate the expected cost of alternative winter forage options and hay feeding systems. The objective of these programs was to help producers assess the potential to reduce the cost of their winter feeding systems. A 120 d winter feeding cost analysis was evaluated to compare the estimated costs of alternative winter forage and hay feeding systems. These cost projections provided a guide to help cow-calf producers develop a cost-effective plan when making decisions on winter feeding. A total of 89 cattle and forage producers from across the Southeast U.S. attended these programs. Participants included large, medium, and small sized operations. Participants completed an evaluation of the program: 90% found the information received to be excellent or good, 86% said it was useful or very useful, 92% said their knowledge had greatly improved, 88% will definitely make changes to management as a result, and 72% will use recommended decision-aid tools. The value of the program information was estimated at 65 per brood cow, average 110,000.
Root‐rhizome mass and chemical composition are important determinants of nutrient cycling and soil C accumulation in grasslands. Adding legumes to grass monocultures increases forage nutritive value and N cycling in animal excreta and aboveground plant litter, but the effects of mixtures on root‐rhizome mass and composition have not been studied extensively. This experiment compared belowground responses of rhizoma peanut (RP, Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flüggé) monocultures with those of their binary mixtures, 3 yr after establishment. Treatments were two bahiagrass entries (‘Argentine’ and DF9, receiving 90 kg N ha⁻¹ harvest⁻¹) and two RP entries (Ecoturf and Q6B) in monoculture, and the combinations of each entry of bahiagrass with each entry of RP. Root‐rhizome biomass in Argentine bahiagrass did not differ from mixtures, but it was greater than RP monocultures in the second year. Total N and C contents were greater in 2016 (P < 0.05, 139 kg N ha⁻¹ and 5360 kg C ha⁻¹) than in 2015 (61 kg N ha⁻¹ and 3540 kg C ha⁻¹) across treatments. In 2016, C/N ratio in mixture belowground biomass was equivalent to that of N‐fertilized bahiagrass monocultures. Bahiagrass and RP belowground proportion did not differ among the mixtures. There was a significant change (P < 0.05) in the Argentine δ¹⁵N from −0.76 to 1.68‰ from 2015 to 2016, respectively. Results indicated that mixing legumes and grasses is a good strategy to improve storage of belowground N in root and rhizome, even compared with bahiagrass fertilized with 90 kg N ha⁻¹ harvest⁻¹.
Fertilization of perennial grass pastures is a major expense in beef cattle operations, and grass pastures may degrade in the absence of N fertilization. Grass–legume mixtures can reduce the demand for N fertilizer use while increasing productivity of the system. Arachis spp. have shown potential for use in association with grasses in the southeastern United States. During 2014, 2015, and 2016, we evaluated one annual peanut species (Arachis hypogaea L. TUFRunner ‘727’) and two perennial peanut species, pintoi peanut (A. pintoi Krap. & W.C. Greg ‘Amarillo’) and rhizoma peanut (A. glabrata Benth. ‘Florigraze’ and germplasm Ecoturf), when planted into previously established ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) sod. Responses measured included herbage accumulation (HA), botanical composition, nutritive value, biological N2 fixation, and belowground root‐rhizome responses. TUFRunner 727 showed reseeding ability, illustrating potential for use as a short‐term forage, but by 2016, its contribution was negligible. In 2016, Ecoturf–bahiagrass had greater HA than unfertilized bahiagrass (4160 and 2710 kg ha⁻¹, respectively), and the Ecoturf contribution to HA was ∼30% in 2016. Average N concentrations for Ecoturf and Florigraze were 25 and 22 g kg⁻¹, respectively, and in vitro digestible organic matter concentration was 700 g kg⁻¹ for both. Pintoi peanut contributed little to mixture HA in the first 2 yr, but it persisted and increased in proportion with time. Over the course of 3 yr, Ecoturf rhizoma peanut performed better than all other entries, exhibiting increasing participation in mixtures each year and the greatest total HA in 2016.
Ruminant livestock have the ability to produce high-quality human food from feedstuffs of little or no value for humans. Balanced essential amino acid composition of meat and milk from ruminants makes those protein sources valuable adjuncts to human diets. It is anticipated that there will be increasing demand for ruminant proteins in the future. Increasing productivity per animal dilutes out the nutritional and environmental costs of maintenance and rearing dairy animals up to production. A number of nutritional strategies improve production per animal such as ration balancing in smallholder operations and small grain supplements to ruminants fed high-forage diets. Greenhouse gas emission intensity is reduced by increased productivity per animal; recent research has developed at least one effective inhibitor of methane production in the rumen. There is widespread over-feeding of protein to dairy cattle; milk and component yields can be maintained, and sometimes even increased, at lower protein intake. Group feeding dairy cows according to production and feeding diets higher in rumen-undegraded protein can improve milk and protein yield. Supplementing rumen-protected essential amino acids will also improve N efficiency in some cases. Better N utilization reduces urinary N, which is the most environmentally unstable form of excretory N. Employing nutritional models to more accurately meet animal requirements improves nutrient efficiency. Although smallholder enterprises, which are concentrated in tropical and semi-tropical regions of developing countries, are subject to different economic pressures, nutritional biology is similar at all production levels. Rather than milk volume, nutritional strategies should maximize milk component yield, which is proportional to market value as well as food value when milk nutrients are consumed directly by farmers and their families. Moving away from Holsteins toward smaller breeds such as Jerseys, Holstein-Jersey crosses or locally adapted breeds (e.g. Vechur) would also reduce lactose production and improve metabolic, environmental and economic efficiencies. Forages containing condensed tannins or polyphenol oxidase enzymes have reduced rumen protein degradation; ruminants capture this protein more efficiently for meat and milk. Although these forages generally have lower yields and persistence, genetic modification would allow insertion of these traits into more widely cultivated forages. Ruminants will retain their niches because of their ability to produce valuable human food from low value feedstuffs. Employing these emerging strategies will allow improved productive efficiency of ruminants in both developing and developed countries.
Use of Jiggs bermudagrass [Cynodon dactylon (L.) Pers.] for hay has increased in warm climates like southern Florida, but effects of defoliation and K fertilizer management on Jiggs adaptation to environments with frequent winter freezes are not known. During 2 yr, K fertilization (0, 17, and 34 kg K ha⁻¹ harvest⁻¹) and cutting stubble height (SH, 8 and 16 cm every 28 d) effects on herbage accumulation (HA), ground cover, K removal, and tissue and soil K were evaluated for Jiggs and ‘Tifton 85’ (Cynodon spp.) bermudagrasses. All treatments received 240 kg N ha⁻¹ yr⁻¹. Herbage accumulation was greater for 8‐ than 16‐cm SH (8050 and 7330 kg ha⁻¹ yr⁻¹, respectively) and increased linearly from 7040 to 8120 kg ha⁻¹ yr⁻¹ with increasing K fertilization. Potassium fertilization did not affect grass percentage ground cover, but Jiggs had 17 (2014) and 40% (2015) greater cover than Tifton 85. Increasing K fertilization increased tissue K concentration (15 to 19 g kg⁻¹ in 2014 and 13 to 25 g kg⁻¹ in 2015) and K removal in HA (from 104 to 149 kg ha⁻¹ in 2014 and 88 to 216 kg ha⁻¹ in 2015). During 2 yr, soil‐extractable K declined 6 mg kg⁻¹ for the zero K level but increased 6 mg kg⁻¹ when K was applied. In a cooler subtropical region characterized by frequent winter freezes and across a range of K fertilizer and SH levels, Jiggs sustained ground cover better than Tifton 85, but K fertilization did not affect persistence.
Despite scientific evidence suggesting that warm-season grasses can respond favorably to K and P fertilization, the increasing costs of fertilizers limit the extent to which these nutrients are used in pastures and hayfields. Two field studies evaluated ‘Jiggs’ bermudagrass [Cynondon dactylon (L.) Pers.] and ‘Floralta’ limpograss (Hemarthria altissima Stapf. and Hubbard) herbage accumulation (HA), nutritive value, and persistence to reduced fertilization strategies during 2012 to 2014. Treatments were allocated in a split-plot design with N (90 or 180 kg N ha−1, bermudagrass study) or harvest frequency (6 vs. 12 wk, limpograss study) as the main factors and P (0, 8.7, and 17.4 kg P ha−1) and K (0, 33, and 66 kg K ha−1) levels as subplots. Bermudagrass HA increased linearly (up to 377% in Year 3) as K level increased. Similarly, K fertilization increased limpograss HA from 8.4 to 11.6 Mg ha−1 in 2013 and from 5.8 to 15.7 Mg ha−1 in 2014 as K levels increased from 0 to 66 kg K ha−1; however, no effect was observed in 2012. Bermudagrass HA and ground cover decreased from 2012 to 2014 in all K treatments. Conversely, decreases in limpograss HA and ground cover over time were observed only in the control (no K) treatments. Bermudagrass and limpograss crude protein concentrations generally decreased with increased K level. No effects of N or P were observed. Continuous aboveground removal without proper K fertilization is detrimental to bermudagrass and limpograss production and persistence.
The prevailing discourse on the future of agriculture is dominated by an imbalanced narrative that calls for food production to increase dramatically—potentially doubling by 2050—without specifying commensurate environmental goals. We aim to rebalance this narrative by laying out quantitative and compelling midcentury targets for both production and the environment. Our analysis shows that an increase of approximately 25%–70% above current production levels may be sufficient to meet 2050 crop demand. At the same time, nutrient losses and greenhouse gas emissions from agriculture must drop dramatically to restore and maintain ecosystem functioning. Specifying quantitative targets will clarify the scope of the challenges that agriculture must face in the coming decades, focus research and policy on achieving specific outcomes, and ensure that sustainable intensification efforts lead to measurable environmental improvements. We propose new directions for research and policy to help meet both sustainability and production goals.
Cynodon grasses are a major feed source for livestock in the US Gulf Coast region. Although continuous stocking is widely used for regional perennial grass pastures, there has been limited evaluation of animal performance on continuously stocked bermudagrass [Cynodon dactylon (L.) Pers.]. This 3‐yr experiment compared forage and animal performance on continuously stocked ‘Tifton 85’ (Cynodon spp.) and ‘Florakirk’ bermudagrass pastures using a variable stocking rate during summer (average of 159 d yr⁻¹). Tifton 85 had greater herbage accumulation than Florakirk (average of 13.6 vs. 7.5 Mg ha⁻¹ yr⁻¹, respectively), in part because Florakirk percentage cover declined from 89% at initiation of the experiment to 35% after 3 yr. Change in cover of Tifton 85 over the same period was 93 to 90%. The Tifton 85 forage concentrations of in vitro digestible organic matter was greater than for Florakirk (563 vs. 523 g kg⁻¹, respectively), but yearling cattle average daily gain did not differ between grasses (0.61 kg d⁻¹). Greater herbage accumulation for Tifton 85 resulted in a greater average stocking rate than for Florakirk (6.4 vs. 3.8 head ha⁻¹, respectively) at a similar herbage allowance of approximately 1.0 kg forage dry matter kg⁻¹ animal body weight. Gain ha⁻¹ was greater for cattle grazing on Tifton 85 than on Florakirk (638 vs. 358 kg ha⁻¹, respectively). Tifton 85 was superior to Florakirk bermudagrass under continuous stocking in northern Florida because of its greater herbage accumulation, herbage in vitro digestible organic matter, average stocking rate, animal gain ha⁻¹, and persistence.
This edition updates a narrative that has been at the forefront of soil science for more than a century. The first edition, published in 1909, was largely a guide to good soil management for farmers in the glaciated regions of New York State in the northeastern U.S. Since then, it has evolved to provide a globally relevant framework for an integrated understanding of the diversity of soils, the soil system and its role in the ecology of planet Earth.
The 15th edition is the first to feature full-color illustrations and photographs throughout. These new and refined full color figures and illustrations help make the study of soils more efficient, engaging, and intellectually satisfying. Every chapter has been thoroughly updated with the latest advances, concepts, and applications. Hundreds of new key references have been added. The 15th edition, like preceding editions, has greatly benefited from innumerable suggestions, ideas, and corrections contributed by soil scientists, instructors, and students from around the world. Dr. Nyle Brady, although long in retirement and recently deceased, remains as co-author in recognition of the fact that his vision, wisdom and inspiration continue to permeate the entire book.
This edition,1082 pages in length, includes in-depth discussions on such topics of cutting edge soil science as the pedosphere concept, new insights into humus and soil carbon accumulation, subaqueous soils, soil effects on human health, principles and practice of organic farming, urban and human engineered soils, cycling and plant use of silicon, inner- and outer-sphere complexes, radioactive soil contamination, new understandings of the nitrogen cycle, cation saturation and ratios, acid sulfate soils, water-saving irrigation techniques, hydraulic redistribution, cover crop effects on soil health, soil food-web ecology, disease suppressive soils, soil microbial genomics, indicators of soil quality, soil ecosystem services, biochar, soil interactions with global climate change, digital soil maps, and many others. In response to their popularity in recent editions, I have also added many new boxes that present either fascinating examples and applications or technical details and calculations. These boxes both highlight material of special interest and allow the logical thread of the regular text to flow smoothly without digression or interruption.
For students: This book provides both an exciting, accessible introduction to the world of soils as well as a reliable, comprehensive reference that you will want to keep for your professional bookshelf. What you learn from its pages will be of enormous practical value in equipping you to meet the many natural-resource challenges of the 21st century. The book demonstrates how the soil system provides many opportunities to see practical applications for principles from such sciences as biology, chemistry, physics, and geology. Throughout, the text highlights the countless interactions between soils and other components of forest, range, agricultural, wetland, and constructed ecosystems.
As the global economy expands exponentially societies face new challenges with managing their natural resources. Soil as a fundamental natural resource is critical to sustained economic growth and the prosperity of people in all parts of the world. To achieve balanced growth with a sustainable economy while improving environmental quality, it will be necessary to have a deep understanding of soils, including their properties, functions, ecological roles and management. I have tried to write this textbook in a way designed to engage inquisitive minds and challenge them to understand soils and actively do their part as environmental and agricultural scientists, in the interest of ensuring a prosperous and healthy future for humanity on planet Earth. It is my sincere hope that this book, previous editions of which have served so many generations of soil students and scientists, will continue to help future generations of soil scientists to benefit from a global ecological view of soils.
The conservation of biodiversity in intensively managed agricultural landscapes depends on the amount and spatial arrangement of cultivated and natural lands. Conservation incentives that create semi-natural grasslands may increase the biodiversity of beneficial insects and their associated ecosystem services, such as pollination and the regulation of insect pests, but the effectiveness of these incentives for insect conservation are poorly known, especially in North America. We studied the variation in species richness, composition, and functional-group abundances of bees and predatory beetles in conservation grasslands surrounded by intensively managed agriculture in Southwest Ohio, USA. Characteristics of grassland patches and surrounding land-cover types were used to predict insect species richness, composition, and functional-group abundance using linear models and multivariate ordinations. Bee species richness was positively influenced by forb cover and beetle richness was positively related to grass cover; both taxa had greater richness in grasslands surrounded by larger amounts of semi-natural land cover. Functional groups of bees and predatory beetles defined by body size and sociality varied in their abundance according to differences in plant composition of grassland patches, as well as the surrounding land-cover diversity. Intensive agriculture in the surrounding landscape acted as a filter to both bee and beetle species composition in conservation grasslands. Our results support the need for management incentives to consider landscape-level processes in the conservation of biodiversity and ecosystem services.
Forage legumes increase nutritive value and provide N to grass-based grazing systems. Few legumes have a long stand life in the southeastern US, but persistence is documented for rhizoma peanut (RP; Arachis glabrata Benth.). Several RP introductions have been released recently from the University of Florida, but their responses to grazing management have not been evaluated. The objective was to determine productivity, persistence, and nutritive value of three RP cultivars (‘Florigraze’, ‘UF Peace’, and ‘UF Tito’) and the germplasm Ecoturf grazed every 3 or 6 wk to remove 50 or 75% of pre-grazing canopy height. Herbage accumulation (HA) was not different among RP entries and averaged 8790 and 6210 kg ha-1 in Years 1 and 2, respectively. Greater HA occurred for the regrowth interval of 6 wk vs. 3 wk in the 50% removal treatment (8040 and 7010 kg ha-1, respectively), and the response approached significance (P = 0.073) for the 75% treatment (7800 vs. 7140 kg ha-1, respectively). Treatments had minimal effect on nutritive value, and all entries had crude protein (CP) ≥ 140 g kg-1 and in vitro digestible organic matter (IVDOM) ≥ 660 g kg-1. Grass encroachment was greater in Ecoturf and Florigraze when grazed every 3 wk (13 and 24%, respectively) than every 6 wk (7 and 15%, respectively), but regrowth interval did not affect grass percentage in Peace and Tito. New RP cultivars and germplasm had similar HA as Florigraze, but also greater percentage RP and lesser weed frequency than Florigraze, especially under frequent or close grazing. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Pastureland, which includes improved, native, and naturalized pastures, accounts for 51 Mha of the 212 Mha of privately held grazing land in the U.S. (Sobecki et al., Ch. 2). This chapter focuses on improved pasture in humid regions (>625 mm mean annual precipitation).
Soil organic matter (SOM) is an important natural resource. It is fundamental to soil and ecosystem functions across a wide range of scales, from site-specific soil fertility and water holding capacity to global biogeochemical cycling. It is also a highly complex material that is sensitive to direct and indirect human impacts. In SOM research, simulation models play an important role by providing a mathematical framework to integrate, examine, and test the understanding of SOM dynamics. Simulation models of SOM are also increasingly used in more 'applied' settings to evaluate human impacts on ecosystem function, and to manage SOM for greenhouse gas mitigation, improved soil health, and sustainable use as a natural resource. Within this context, there is a need to maintain a robust connection between scientific developments in SOM modeling approaches and SOM model applications. This need forms the basis of this review. In this review we first provide an overview of SOM modeling, focusing on SOM theory, data-model integration, and model development as evidenced by a quantitative review of SOM literature. Second, we present the landscape of SOM model applications, focusing on examples in climate change policy. We conclude by discussing five areas of recent developments in SOM modeling including: (1) microbial roles in SOM stabilization; (2) modeling SOM saturation kinetics; (3) temperature controls on decomposition; (4) SOM dynamics in deep soil layers; and (5) SOM representation in earth system models. Our aim is to comprehensively connect SOM model development to its applications, revealing knowledge gaps in need of focused interdisciplinary attention and exposing pitfalls that, if avoided, can lead to best use of SOM models to support policy initiatives and sustainable land management solutions.
Non-steady-state (NSS) chambers offer the best available tool for statistically evaluating effects of management practices on soil greenhouse gases (GHG) emissions. However, limitations of NSS chambers for determining soil-to-atmosphere gas exchange rates have been recognized for decades. In particular, the tendency for NSS chambers to produce a biased estimate of the actual pre-deployment flux can be important for GHGs like nitrous oxide which often requires prolonged chamber deployment periods. Despite widespread recognition, there is little consensus regarding approaches to reduce the magnitude of this effect. Recent analysis has shown that intra- and inter-site flux comparisons can be confounded by chamber-induced artifacts, which has important implications for effective GHG mitigation. The objective of this chapter is to describe and discuss the physical basis of the problem and how it is influenced by measurement methods and soil properties, available options for quantifying and minimizing biases, and the path toward ultimate solutions.
Grazing experiments provide fundamental information on the biology of grassland ecosystems, enable selection of persistent forage cultivars that support animal production, and develop management guidelines for end users. Challenges to proper conduct of grazing research include achieving meaningful time and spatial scales, difficulty in measurement of key variables, and scarcity of research funding. Opportunities are emerging for grazing research as a result of increasing awareness of grassland multifunctionality, ecosystem services, and environmental impacts. Capitalizing on these opportunities will require increased participation in grazing research by collaborators from a broader range of ecosystem sciences. This facilitates answering traditional production questions while concurrently discovering new knowledge regarding the larger grassland agroecosystem. Application of grazing research implies adoption by clientele and achieving real‐world impacts. Targeting technology and products to specific clientele and achieving on‐farm participation by change agents within the target audience can provide highly visible pilot studies that attract users to new technologies. The future of grazing research is not assured, but opportunities are emerging for scientists who engage collaborators representing a broader range of ecosystem sciences and who effectively develop and communicate their program outputs to clientele leading to adoption and measurable impacts.
Bermudagrass is a dominant hay crop in Florida. Now, hay producers are facing a new emerging pest problem in bermudagrass and stargrass production fields. The bermudagrass stem maggot is a new exotic invasive fly. It was first discovered damaging bermudagrass pasture and hay fields in Georgia. The identification of the fly was the first record of this species in North America, and it has the potential to become a serious pest of bermudagrass and stargrass in Florida. This 2-page fact sheet was written by Ann Blount, Tim Wilson, Jay Ferrell, Russ Mizell, and Jonael Bosques, and published by the UF Department of Agronomy, June 2014. SS-AGR-379/AG384: Bermudagrass Stem Maggot—A New Pest in Florida (ufl.edu)
AN234, a 6-page fact sheet by Bob Myer, Lori Warren, Juliet Eckert, Dennis Hancock, Ann Blount, and Clay Olson, summarizes nutritional composition data and results of animal feeding studies, including studies with horses. Includes references. Published by the UF Department of Animal Sciences, February 2010. AN234/AN234: Perennial Peanut: Forage Nutritional Composition and Feeding Value (ufl.edu)
In this study we conducted four field trials (two wet- and two dry-season) to quantify N2O and CH4 emissions, NH3 volatilization, and N2O emission factors (EF3PRP) following the application of cattle dung, urine, dung plus urine, and urea fertilizer on a palisade-grass pastureland in Brazil. The EF3PRP differed with treatment and season. Wet season EF3PRP were 0.36%, 1.02%, and 0.84% and dry season EF3PRP were 0.32%, 0.47%, and 0.34% for dung, urine, and dung plus urine, respectively. These emission factors are maybe lower than the default proposed by the Intergovernmental Panel on Climate Change (IPCC; 2%). Methane emissions also differed according to the treatment and season, and annualized dung emissions were 0.54 kg CH4 head−1 year−1. The fraction of total-N from animal manure and urine emitted as NH3 (FracGASM) in the wet season for dung, urine and dung plus urine was 7.2%, 6.3%, and 6.4%, respectively; lower than the rate of dry season volatilization from urine (14.2%) and dung plus urine (11.5%). Observed FracGASM is probably lower than the IPCC guideline (20%). Emissions of N2O, CH4, and the volatilization of NH3 after urea treatment were not influenced by season; N2O emissions from urea were 0.85%, CH4 emissions were 112 g CH4-C ha−1, and N-fertilizer lost as NH3 was 16.9%. The emission factors observed in this experiment differed from the IPCC Guidelines; observed N2O emissions were lower than the guideline (1%), and FracGASF was higher than the 10% guideline.
Core Ideas
Grass reduced lag phase and increased legume decomposition in mixtures relative to monocultures.
Factors besides litter chemical composition, such as microbial diversity, affected decomposition.
Legume treatments were enriched and grass monoculture depleted in δ¹³C during decomposition.
Availability of C, and to a greater extent N, decreased during decomposition.
ABSTRACT
The impact of legume inclusion on the decomposition of aboveground plant litter in grasslands is not well understood. Our objective was to quantify litter decomposition and nutrient disappearance from ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) as affected by N fertilizer or proportion of ‘Florigraze’ rhizoma peanut (Arachis glabrata Benth.) in litter. Five litter treatments (unfertilized bahiagrass [BG], bahiagrass receiving 60 kg N ha⁻¹ [BGN], rhizoma peanut and bahiagrass mixtures in 33–67% and 67–33% proportions [RP33 and RP67, respectively], and pure rhizoma peanut [RP]) were incubated for 128 d during each of 2 yr. Decomposition followed a logistic curve with a linear decay between initial and final lag phases. Litter treatment did not affect decomposition rate, but RP33 litter decomposed to a greater extent than BG (35 and 43% remaining biomass, respectively) due to a longer linear decay period for RP33. At the end of incubation, only 25% of the initial rhizoma peanut component litter mass remained for RP33, whereas 35 and 39% remained for RP67 and RP. Bahiagrass decomposition was not affected by the presence of legume. Bahiagrass monocultures showed δ¹³C depletion, and all legume‐containing treatments showed δ¹³C enrichment during incubation. After incubation, there was less N in legume litter treatments despite similar chemical characteristics to BGN, indicating that other factors, such as microbial diversity, affected mixture decomposition. Recalcitrance of C and especially N increased during decomposition. We conclude that N return from mixed legume–grass litter is superior to that of unfertilized grass and equal or superior to that of moderately N‐fertilized grass.
Pintoi peanut (Arachis pintoi Krapov. & W.C. Greg.) is a warm‐season perennial legume with potential for use in grass–legume mixtures in Florida; however, limited information exists about its establishment in mixtures with bahiagrass (Paspalum notatum Flügge). The objective of this experiment was to evaluate the establishment of bahiagrass cv. “Argentine” and pintoi peanut cv. “Amarillo” as monocultures or mixture. The experiment was conducted in Ona, FL, from June to October of 2014 and 2015. Treatments were a split‐plot design of seeding strategies (bahiagrass monoculture, pintoi peanut monoculture or bahiagrass‐pintoi peanut mixtures; main plots) and two N fertilization strategies (30 or 80 kg/ha N; 30N and 80N; subplots), with four replicates. Measurements of plant density and frequency were taken every 4 weeks after seeding. Ground cover and herbage mass (HM) measurements were taken 112 days after seeding. Pintoi peanut ground cover was affected by seeding strategy × N level interaction. Ground cover was greater with 80N than 30N when pintoi was seeded in monoculture (3.6% vs 1.5% respectively) but not when it was seeded with bahiagrass (2.1%). There was no effect of seeding or N strategy on pintoi peanut proportion in HM (1.4%). Bahiagrass ground cover was not affected by seeding or N strategy (15.9%); however, its proportion in the HM was greater in 80N than 30N (12.1% vs 9.4% respectively). Mixed seeding did not negatively affect the establishment of bahiagrass and pintoi peanut and greater N fertilization levels improved some establishment parameters, with no negative effect for pintoi peanut.
Grazing lands represent the largest and most diverse land resource-taking up over half the earth's land surface. The large area grazing land occupies, its diversity of climates and soils, and the potential to improve its use and productivity all contribute to its importance for sequestering C and mitigating the greenhouse effect and other conditions brought about by climate change. The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect gives you an in-depth look at this possibility.
To predict the behavior of the terrestrial carbon cycle, it is critical to understand the source, formation pathway, and chemical composition of soil organic matter (SOM). There is emerging consensus that slow‐cycling SOM generally consists of relatively low molecular weight organic carbon substrates that enter the mineral soil as dissolved organic matter and associate with mineral surfaces (referred to as ‘mineral‐associated OM’, or MAOM). However, much debate and contradictory evidence persists around: (1) whether the organic C substrates within the MAOM pool primarily originate from aboveground versus belowground plant sources, and (2) if C substrates directly sorb to mineral surfaces or undergo microbial transformation prior to their incorporation into MAOM. Here, we attempt to reconcile disparate views on the formation of MAOM by proposing a spatially‐explicit set of processes that link plant C source with MAOM formation pathway. Specifically, because belowground versus aboveground sources of plant C enter spatially distinct regions of the mineral soil, we propose that fine‐scale differences in microbial abundance should determine the probability of substrate‐microbe versus substrate‐mineral interaction. Thus, formation of MAOM in areas of high microbial density (e.g. the rhizosphere and other microbial hotspots) should primarily occur through an in vivo microbial turnover pathway, and favor C substrates that are first biosynthesized with high microbial carbon‐use efficiency prior to incorporation in the MAOM pool. In contrast, in areas of low microbial density (e.g. certain regions of the bulk soil), MAOM formation should primarily occur through the direct sorption of intact or partially oxidized plant compounds to un‐colonized mineral surfaces, minimizing the importance of carbon use efficiency, and favoring C substrates with strong ‘sorptive affinity’. Through this framework, we thus describe how the primacy of biotic versus abiotic controls on MAOM dynamics are not mutually exclusive, but rather spatially dictated. Such an understanding may be integral to more accurately modeling soil organic matter dynamics across different spatial scales. This article is protected by copyright. All rights reserved.
Globally, consumption of bovine meat is projected to increase by 1.2% per annum until 2050, a demand likely met in part by increased Canadian beef production. With this greater production on a finite agricultural land base, there is a need to weigh the contribution of this industry to the Canadian economy against the full range of positive and negative ecological and social impacts of beef production. This review, focussing on the prairie provinces of Alberta, Saskatchewan and Manitoba, which collectively support just over 80% of the Canadian beef herd, examines the social and ecological footprint of the cow-calf, backgrounding, finishing and forage/feed production stages of beef production within an ecosystem services framework. We summarise the literature on how beef production and management practices affect a range of services, including livestock; water supply; water, air and soil quality; climate regulation; zoonotic diseases; cultural services; and biodiversity. Based on 742 peer-reviewed publications, spanning all agricultural stages of beef production, we established a framework for identifying management practices yielding the greatest overall socio-ecological benefits in terms of positive impacts on ecosystem service supply. Further, we identified research gaps and crucial research questions related to the sustainability of beef production systems.
Forage–livestock systems in the southeastern United States are based on N-fertilized perennial grass pastures, with minimal legume contribution. The legume rhizoma peanut (RP, Arachis glabrata Benth.) can persist and spread in grazed mixtures with C4 grasses, and Ecoturf RP is of particular interest because it is relatively decumbent and may vary its growth habit in response to defoliation management. The objective was to quantify effects of grazing frequency and intensity of Ecoturf on herbage accumulation (HA), canopy characteristics, storage organ mass, and total nonstructural carbohydrate (TNC) concentration. Treatments were the factorial combinations of three levels of regrowth interval (RI; 1, 4, and 7 wk) between grazing events and two levels of post-grazing stubble height (SH; 4 and 8 cm). For the 4-cm SH, HA increased from 8.4 to 10.5 Mg ha⁻¹ in 2015 and from 9.8 to 13.6 Mg ha⁻¹ in 2016 as RI decreased from 7 to 1 wk. The effect of RI was less pronounced for the 8-cm SH. When grazed to a 4-cm SH, herbage bulk density and post-grazing leaflet mass increased linearly as RI decreased from 7 to 1 wk in both years. Changes in root-rhizome mass and TNC pool during 2 yr of grazing were not affected by SH or RI. Ecoturf adapted to frequent, close grazing by increasing herbage bulk density and positioning leaves close to the soil surface, allowing rapid regrowth after defoliation without depleting reserves. Ecoturf is tolerant of a range of grazing strategies, showing promise for use in pastures. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Warm-climate grasslands are often N limited. Legume litter decomposition can contribute significantly to N input in grazing systems, but its contribution depends on litter deposition, decomposition, and chemical composition. We evaluated these responses for 2 yr in unfertilized (BG) and fertilized (BGN; 50 kg N ha−1) bahiagrass (Paspalum notatum Flügge) monocultures and in mixed swards of bahiagrass plus the legume rhizoma peanut (Arachis glabrata Benth.). Legume–grass mixture litter had greater initial N concentration (26 g N kg−1 organic matter [OM]) and lower C/N ratio (22) than BG and BGN, which did not differ from each other (18 g N kg−1 OM, C/N ratio of 31). Litter biomass relative decay rate was greater for mixtures than for bahiagrass monocultures. As a result, less biomass and N remained at the end of incubation in mixtures (62 and 76%, respectively) than in monocultures (69 and 80%, respectively). Litter deposition rate was similar across treatments, but faster decomposition and greater N concentration for legume–grass mixtures resulted in larger litter N release than in monocultures (44 and 26 kg ha−1, respectively). At the end of incubation, remaining litter biomass and remaining N decreased with increasing litter legume proportion, whereas litter N concentration and litter decay rate increased. Results indicate that legume–grass mixtures are an alternative to N fertilizer for increasing N cycling through plant litter in grasslands, and although litter deposition rates were similar across treatments, increasing legume proportion in mixtures is likely to be associated with greater litter N release.
Grasslands in warm-climate regions are often based on grass monocultures, increasing their dependence on N fertilizers. Integrating perennial legumes into grass pastures is a logical option. The objective of this 2-yr study was to assess seven rhizoma peanut (Arachis glabrata Benth) cultivars: Arbrook, Arblick, Ecoturf, Florigraze, Latitude 34, UF Peace, and UF Tito. Above- and belowground responses included biomass, in vitro organic matter disappearance (IVOMD), N concentration, N content, δ¹⁵N, proportion of N derived from atmosphere (%Ndfa), and biological N2 fixation (BNF). Arbrook was more productive than Florigraze in both years (P ≤ 0.05) but produced similar biomass to other varieties in 2014. In 2015, Arbrook also was more productive than Arblick and Latitude 34. Herbage N concentration ranged from 19.2 to 36.3 g kg⁻¹. Arbrook tended to be less digestible than other rhizoma peanut cultivars. The BNF represented >80% of herbage N and averaged 200 kg N ha⁻¹ yr⁻¹, with values ranging from 123 to 280 kg N ha⁻¹ yr⁻¹. Root and rhizome biomass varied among cultivars, with Ecoturf (26.9 Mg organic matter [OM] ha⁻¹) and Latitude 34 (27.8 Mg OM ha⁻¹) presenting greater root and rhizome mass than Florigraze (10.5 Mg OM ha⁻¹) but similar to other varieties. Roots and rhizomes represented a significant portion of the total biomass and N pool, and further studies are needed to assess turnover of these tissues as well as their N contribution in grazing systems using grass-rhizoma peanut mixtures. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Nitrogen (N) fertilization affects grassland herbage accumulation and nutritive value, but its effect on the distribution of nutrients among soil and plant nutrient pools is less understood. This 2-yr study determined the effect of N fertilization levels of rotationally stocked ‘Tifton 85’ bermudagrass (Cynodon spp.) pastures on nutrient concentration and content in soil (top 20 cm), live root-rhizome mass, live herbage mass, and aboveground plant litter pools. Treatments were 50, 150, and 250 kg N ha⁻¹ yr⁻¹. Greater N fertilization increased N concentration in all plant nutrient pools and potassium (K) concentration in live herbage and plant litter, but plant-pool phosphorus (P) concentrations changed little across N levels. With increasing N fertilization, live herbage (118–159 kg ha⁻¹) and plant litter (8–14 kg ha⁻¹) K pools increased linearly, but the Mehlich-1 extractable soil K pool decreased linearly (182–139 kg ha⁻¹); live herbage (50–92 kg ha⁻¹), plant litter (30–49 kg ha⁻¹), and root rhizome (63–95 kg ha⁻¹) N pools also increased with increasing N fertilization. The proportion of K in various pools was affected more by N fertilization than were proportions of N, P, or carbon. Soil was the dominant pool for all nutrients, with the exception of K in pastures fertilized at the greatest N level. Increasing N fertilization increased the proportion of K and N contained in plant pools and decreased the proportion in soil. Although N fertilization affected quantity and proportion of nutrients in pools in Tifton 85 pastures, changes occurred to a limited extent, with the exception of plant and soil K pools.
Grassland ecosystems cover a large portion of the Earths' surface and contain substantial amounts of soil organic carbon. Previous work has established that these soil carbon stocks are sensitive to management and land use changes - grazing, species composition, and mineral nutrient availability can lead to losses or gains of soil carbon. Because of the large annual carbon fluxes into and out of grassland systems, there has been growing interest in how changes in management might shift the net balance of these flows - stemming losses from degrading grasslands or managing systems to increase soil carbon stocks (i.e., carbon sequestration). A synthesis published in 2001 assembled data from hundreds of studies to document soil carbon responses to changes in management. Here we present a new synthesis that has integrated data from the hundreds of studies published after our previous work. These new data largely confirm our earlier conclusions: improved grazing management, fertilization, sowing legumes and improved grass species, irrigation, and conversion from cultivation all tend to lead to increased soil C - at rates ranging from 0.105 to more than 1 Mg C ha(-1) yr(-1) . The new data include assessment of three new management practices: fire, silvopastoralism, and reclamation, although these studies are limited in number. The main area in which the new data are contrary to our previous synthesis is in conversion from native vegetation to grassland, where we find that across the studies the average rate of soil carbon stock change is low and not significant. The data in this synthesis confirm that improving grassland management practices and conversion from cropland to grassland improve soil carbon stocks. This article is protected by copyright. All rights reserved.
‘Florigraze’ rhizoma peanut (RP; Arachis glabrata Benth.) is a persistent forage legume for the US Gulf Coast, but peanut stunt virus (Cucumovirus spp.) reduces herbage accumulation (HA). Less susceptible germplasms and cultivars of RP have been released, but their responses to grazing management are not known. The objective was to quantify aboveground and belowground sward responses to grazing management of RP entries differing in growth habit to explain HA and persistence. Treatments were all combinations of four RP entries (Florigraze, ‘UF Peace’, ‘UF Tito’, and germplasm Ecoturf), two grazing intensities (50 and 75% removal of pre-grazing canopy height), and two regrowth intervals (3 or 6 wk). UF Tito swards were the tallest and Ecoturf the shortest, but Ecoturf had greater herbage bulk density than any entry. Pre-grazing Ieaf percentage was greatest for Ecoturf (61%); there were no differences among the upright entries (56-57%). Ecoturf (0.88) and UF Tito (0.76) had greater post-grazing residual Ieaf area index than Florigraze (0.61). Ecoturf and UF Tito had greater rhizome-root mass (4450 and 4110 kg ha-1, respectively) than Florigraze and UF Peace (3490 and 3170 kg ha-1, respectively). Pre-grazing light interception was greater for the 6- than 3-wk grazing frequency (85 vs. 70%, respectively), and rhizome-root mass followed a similar pattern (3990 vs. 2730 kg ha-1, respectively). Sward structure, leaf, and rhizome-root data explain Iack of differences among entries in HA, excellent persistence of Ecoturf and UF Tito, and generally greater HA and persistence for 6- vs. 3-wk regrowth intervals. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Pasture dry matter (DM) {TOTAL, LIVE [total - dead], GRASS, RP [rhizoma peanut {Arachis glabrata Benth)], and DEAD}, and relative growth rate (RGR), as well as steer (Bos spp.) average-daily gain (ADG) and plasma urea N (PUN) were measured for continuously grazed grass-RP or bahiagrass (BG) (Paspalum notatum Flugge) in the summers of 1986 and 1987. Crude protein (CP) and in vitro organic matter digestibility (IVOMD) was determined for GRASS and RP. The LIVE DM of the grass-RP sward was higher than the BG sward (P = 0.06 and P = 0.001 in 1986 and 1987, respectively) due to the additive effect of the RP. Above average spring rainfall in 1987 almost doubled forage availability on both sward types. Rhizoma peanut was responsible for most of the increase on the grass-RP sward (GRASS component—508 and 569 lb/acre, RP component—437 and 1433 lb/acre seasonal average in 1986 and 1987, respectively). The GRASS CP and IVOMD of either sward was similar and exhibited a similar pattern of decline during the grazing season (18.6-6.3% CP and 67.4-45.2% IVOMD from April-September). The RP CP and IVOMD was higher throughout the grazing season (28.6-13.9% CP and 78.0-63.6% IVOMD). There was a significant treatment × year interaction for ADG and PUN (BG-1.15 and 1.11 lb ADG and 97 and 85 ppm PUN; grass-RP-1.50 and 1.99 lb ADG and 166 and 235 ppm PUN in 1986 and 1987, respectively). This was due to increased RP in the sward (26% in 1986 and 45% in 1987).
Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © 1991. . Copyright © 1991 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 5585 Guilford Rd., Madison, WI 53711 USA
Increasing recognition of the extent to which nitrous oxide (N
2
O) contributes to climate change has resulted in greater demand to improve quantification of N
2
O emissions, identify emission sources and suggest mitigation options. Agriculture is by far the largest source and grasslands, occupying
c
. 0·22 of European agricultural land, are a major land-use within this sector. The application of mineral fertilizers to optimize pasture yields is a major source of N
2
O and with increasing pressure to increase agricultural productivity, options to quantify and reduce emissions whilst maintaining sufficient grassland for a given intensity of production are required. Identification of the source and extent of emissions will help to improve reporting in national inventories, with the most common approach using the IPCC emission factor (EF) default, where 0·01 of added nitrogen fertilizer is assumed to be emitted directly as N
2
O. The current experiment aimed to establish the suitability of applying this EF to fertilized Scottish grasslands and to identify variation in the EF depending on the application rate of ammonium nitrate (AN). Mitigation options to reduce N
2
O emissions were also investigated, including the use of urea fertilizer in place of AN, addition of a nitrification inhibitor dicyandiamide (DCD) and application of AN in smaller, more frequent doses. Nitrous oxide emissions were measured from a cut grassland in south-west Scotland from March 2011 to March 2012. Grass yield was also measured to establish the impact of mitigation options on grass production, along with soil and environmental variables to improve understanding of the controls on N
2
O emissions. A monotonic increase in annual cumulative N
2
O emissions was observed with increasing AN application rate. Emission factors ranging from 1·06–1·34% were measured for AN application rates between 80 and 320 kg N/ha, with a mean of 1·19%. A lack of any significant difference between these EFs indicates that use of a uniform EF is suitable over these application rates. The mean EF of 1·19% exceeds the IPCC default 1%, suggesting that use of the default value may underestimate emissions of AN-fertilizer-induced N
2
O loss from Scottish grasslands. The increase in emissions beyond an application rate of 320 kg N/ha produced an EF of 1·74%, significantly different to that from lower application rates and much greater than the 1% default. An EF of 0·89% for urea fertilizer and 0·59% for urea with DCD suggests that N
2
O quantification using the IPCC default EF will overestimate emissions for grasslands where these fertilizers are applied. Large rainfall shortly after fertilizer application appears to be the main trigger for N
2
O emissions, thus applicability of the 1% EF could vary and depend on the weather conditions at the time of fertilizer application.
Emissions of nitrous oxide (N2O) from N-fertilized silage grassland in the UK were modelled with a hybrid part-empirical part-mechanistic model, B-LINE 2. N2O fluxes were predicted from combinations of three soil variables: soil water-filled pore space (WFPS), soil temperature (T) and soil mineral N content (Nmin). Pooled field “training” data from several sites and seasons were used to parameterise the model. N2O fluxes were assigned one of three values: the geometric means of the ranges 1–10, 10–100 and 100–1,000 g N2O-N ha−1 day−1, respectively, depending on threshold lines (a) relating flux and Nmin and (b) relating flux, WFPS and T. The model was applied to give daily and seasonal total fluxes, and the overall relationships with measured emissions from ammonium nitrate treatments were analysed separately for those site-seasons not used as a source of training data, for the training data site-seasons, and for all site-seasons together. Results for both training and non-training site-seasons showed, with some exceptions, reasonable agreement with experimental measurements in the timings of main emission peaks, and also in the magnitude of daily flux rate variations over time. Generally, modelled seasonal N2O emissions were somewhat higher than measured values, possibly because at very high WFPS values the actual N2O flux was lower than predicted as a result of greater reduction of nitrate to N2, rather than release as N2O. However, one site was an outlier, with predicted emissions much lower than those observed. Overall, the modelling results compared well with those obtained elsewhere with other models.
The exchange of nutrients, energy and carbon between soil organic matter, the soil environment, aquatic systems and the atmosphere is important for agricultural productivity, water quality and climate. Long-standing theory suggests that soil organic matter is composed of inherently stable and chemically unique compounds. Here we argue that the available evidence does not support the formation of large-molecular-size and persistent 'humic substances' in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds. We discuss implications of this view of the nature of soil organic matter for aquatic health, soil carbon-climate interactions and land management.