Arachis Glabrata Research Articles

Nitrogen leaching and groundwater recharge of alternative lawn conversions in subtropical climates

AbstractClimate change, recurrent droughts, and increasing urban water demands have limited water availability in urban landscapes. Water quantity challenges have led to irrigation restrictions and turfgrass removal programs. An experiment was conducted at the University of Florida, West Florida Research and Education Center, Jay, FL, to evaluate the effect of turfgrass conversion to other landscape types on nutrient leaching and groundwater recharge. In April 2021, all surface vegetation was removed from existing turfgrass plots using a sod harvester. Thereafter, plots were planted or covered with three landscape types: a pollinator landscape with flowering forbs (Mimosa sp., Coreopsis sp., and Phyla sp.) + turfgrass (Eremochloa ophiuroides); a nitrogen (N)‐efficient lawn (Arachis glabrata + Paspalum notatum); and a low‐input landscape with unplanted woodchip mulch. Undisturbed turfgrass (E. ophiuroides) served as a control. For 2 years, leachate samples were collected weekly from previously installed 168‐L drainage lysimeters for NO3‐N and NH4‐N load determination. Temporal changes in landscape composition, groundwater recharge, water use, and soil bulk density were also quantified. While the mulch leached 44.7 kg ha−1 NO3‐N year−1, this landscape still offers positive attributes, including erosion protection and water conservation. Conversely, the pollinator landscape minimized nitrogen leaching (8.3 kg ha−1 NO3‐N year−1) due to their relatively greater water use rates (3.56 mm day−1). The turfgrass and nitrogen‐efficient lawn returned ∼35% of the water inputs as groundwater recharge while maintaining relatively low nitrogen leaching (3.6 and 2.7 kg ha−1 NO3‐N year−1, respectively), making these landscapes efficient for protecting both water quality and quantity.

Integrating Rhizoma Perennial Peanut into Bahiagrass Pastures Enhances Beneficial Soil Microbes in Florida

Integrating Rhizoma Perennial Peanut into Bahiagrass Pastures Enhances Beneficial Soil Microbes in Florida

Forage legume responses to climate change factors

AbstractIncorporating forage legumes into grasslands is a recommended climate change mitigation strategy, but accruing desired benefits from legumes is contingent upon their resilience when exposed to climate change factors (CCF). Our objective was to synthesize literature describing responses to CCF of a broad array of forage legume species, including annuals and perennials from both temperate and tropical/subtropical regions. Most‐represented species in the related literature include alfalfa (Medicago sativa L.), various Trifolium and Lotus species, rhizoma peanut (Arachis glabrata Benth.), and capitata stylo (Stylosanthes capitata Vogel). The data indicate that while CCF effects on forage legumes can be generalized, interactions among CCF, species, and site‐specific soil/climate conditions may cause variation from expected responses. In most instances, exposing forage legumes to CO2 enrichment (eCO2) increased forage accumulation (FA), but elevated temperature (eT) often reduced the magnitude of the positive response to eCO2. Photosynthetic acclimation to eCO2 occurs in non‐N‐fixing plants, but legume nodules are large C sinks and drive sustained increases in legume FA to eCO2. Legume N2 fixation and the proportion of legume N derived from N2 fixation increase with eCO2, but the magnitude of the increases lessens with eT. Legume nutritive value (NV) responses to eCO2 are less pronounced than FA responses, but decreased herbage N and greater nonstructural carbohydrate concentrations are common. Exposure to eT negatively affects NV unless intervals between defoliation events are shortened. Limited data on reproductive performance show CCF affect flower number, pollen grain morphology and viability, and behavior of pollinators, potentially influencing legume reproductive success.

Soil fungal community structure and function response to rhizoma perennial peanut cultivars

BackgroundCrop-associated microorganisms play a crucial role in soil nutrient cycling, and crop growth, and health. Fine-scale patterns in soil microbial community diversity and composition are commonly regulated by plant species or genotype. Despite extensive reports in different crop or its cultivar effects on the microbial community, it is uncertain how rhizoma peanut (RP, Arachis glabrata Benth.), a perennial warm-season legume forage that is well-adapted in the southern USA, affects soil microbial community across different cultivars.ResultsThis study explored the influence of seven different RP cultivars on the taxonomic composition, diversity, and functional groups of soil fungal communities through a field trial in Marianna, Florida, Southern USA, using next-generation sequencing technique. Our results showed that the taxonomic diversity and composition of the fungal community differed significantly across RP cultivars. Alpha diversity (Shannon, Simpson, and Pielou’s evenness) was significantly higher in Ecoturf but lower in UF_Peace and Florigraze compared to other cultivars (p < 0.001). Phylogenetic diversity (Faith’s PD) was lowest in Latitude compared to other cultivars (p < 0.0001). The dominant phyla were Ascomycota (13.34%), Mortierellomycota (3.82%), and Basidiomycota (2.99%), which were significantly greater in Florigraze, UF_Peace, and Ecoturf, respectively. The relative abundance of Neocosmospora was markedly high (21.45%) in UF_Tito and showed large variations across cultivars. The relative abundance of the dominant genera was significantly greater in Arbrook than in other cultivars. There were also significant differences in the co-occurrence network, showing different keystone taxa and more positive correlations than the negative correlations across cultivars. FUNGuild analysis showed that the relative abundance of functional guilds including pathogenic, saprotrophic, endophytic, mycorrhizal and parasitic fungi significantly differed among cultivars. Ecoturf had the greatest relative abundance of mycorrhizal fungal group (5.10 ± 0.44), whereas UF_Peace had the greatest relative abundance of endophytic (4.52 ± 0.56) and parasitic fungi (1.67 ± 0.30) compared to other cultivars.ConclusionsOur findings provide evidence of crop cultivar’s effect in shaping fine-scale fungal community patterns in legume-based forage systems.Graphical abstract

Nitrogen application during rhizoma peanut shoot emergence affects planting‐year nitrogen fixation

AbstractRhizoma peanut (Arachis glabrata Benth.; RP) is an important perennial forage legume in the US Gulf Coast region, but it is vegetatively propagated from rhizomes and relatively slow to establish. There are reports that N fertilization enhances RP establishment, but other evidence suggests plant N content and establishment rate may not benefit. Understanding the effect of N fertilizer on RP biological N2 fixation will help elucidate this response. Our objective was to determine the effect of RP genotype and N fertilization during shoot emergence on N2 fixation and N accumulation during the year of planting. Replicated field experiments were conducted in adjoining fields; one was planted in 2016 and the other in 2017. Treatments were the factorial combinations of two RP entries (decumbent germplasm Ecoturf and upright cultivar ‘UF Tito’) and three N rates (0, 40, and 80 kg N ha−1 applied 10 wk after planting; 1% of total N as 15N) arranged in a randomized complete block design with four replications. Across N rates, upright cultivar UF Tito generally had greater N concentration and content in aboveground and belowground plant parts compared with decumbent germplasm Ecoturf. Nitrogen fertilization generally reduced the percentage of N derived from atmosphere and the amount of fixed N (BNF) during the year of planting, but it did not affect overall N concentration or content. These data suggest RP increased soil N uptake to compensate for reduced BNF following N fertilization, indicating starter N application had no measurable benefit for legume establishment under these conditions.

Herbage responses and animal performance of nitrogen-fertilized grass and grass-legume grazing systems

AbstractThe study evaluated forage and livestock performance in different grazing systems over two years. Treatments were three contrasting grazing systems: (I) N-fertilized bahiagrass (Paspalum notatum Flüggé) in the summer overseeded during the winter by N-fertilized ryegrass (Lolium multiflorum) and oat (Avena sativa L.) (Grass + N); (II) unfertilized bahiagrass during the summer overseeded with ryegrass + oat and a blend of clovers (Trifolium spp.) in the winter (Grass + Clover); (III) unfertilized bahiagrass and rhizoma peanut (RP; Arachis glabrata Benth.) mixture during summer, overseeded during winter by ryegrass + oat + clovers mixture (Grass + Clover + RP). Average daily gain (ADG), gain per area (GPA), and stocking rate (SR) in the winter did not differ across treatments and averaged 0.87 kg/d (P = 0.940), 303 kg/ha, and 2.72 AU/ha. In the summer, Grass + Clover + RP had greater ADG than Grass + N (0.34 vs. 0.17 kg/d, respectively). During the summer, the GPA of Grass + Clover + RP was superior to Grass + N (257 vs. 129 kg/ha, respectively), with no difference in SR among treatments at 3.19 AU/ha. Over the entire year, ADG and GPA tended to be greater for Grass + Clover + RP. Annual SR differed between treatments, where Grass + N was greater (3.37 AU/ha) than the other treatments, which averaged 2.76 AU/ha. Integration of legumes into pasture systems in the summer and winter contributes to developing a sustainable grazing system, reducing N fertilizer use by 85% while tending to increase livestock productivity even though SR was decreased by 18%.

Soil Bacterial Diversity Responds to Long-Term Establishment of Perennial Legumes in Warm-Season Grassland at Two Soil Depths.

The introduction of rhizoma peanut (RP Arachis glabrata Benth) into bahiagrass (Paspalum notatum Flüggé) may require time to develop stable plant-soil microbe interactions as the microbial legacy of the previous plant community may be long-lasting. A previous study showed that <2 years of introducing rhizoma peanut into bahiagrass pastures minimally affected soil bacterial diversity and community composition. In this study, we compared the effects of the long-term inclusion of rhizoma peanut (>8 years) into bahiagrass on soil bacterial diversity and community composition against their monocultures at 0 to 15 and 15 to 30 cm soil depths using next-generation sequencing to target bacterial 16S V3-V4 regions. We observed that a well-established RP-bahiagrass mixed stand led to a 36% increase in bacterial alpha diversity compared to the bahiagrass monoculture. There was a shift from a soil bacterial community dominated by Proteobacteria (~26%) reported in other bahiagrass and rhizoma peanut studies to a soil bacterial community dominated by Firmicutes (39%) in our study. The relative abundance of the bacterial genus Crossiella, known for its antimicrobial traits, was enhanced in the presence of RP. Differences in soil bacterial diversity and community composition were substantial between 0 to 15 and 15 to 30 cm soil layers, with N2-fixing bacteria belonging to the phylum Proteobacteria concentrated in 0 to 15 cm. Introducing RP into bahiagrass pastures is a highly sustainable alternative to mineral N fertilizer inputs. Our results provide evidence that this system also promotes greater soil microbial diversity and is associated with unique taxa that require further study to better understand their contributions to healthy pastures.

Can molecular model crop rice become a boon towards progress of groundnut functional genomics?

Improvement through conventional breeding is a big problem in developing diverse lines of groundnut on tackling good seed quality. A total of 25 markers targeting 13 known rice genes were evaluated with 24 groundnut genotypes and two wild groundnut genotypes (Arachis glabrata, Arachis villosa) and a local popular rice variety NLR34449 (Nellore Mashuri) as molecular check. It was very interesting to note that amplification of 17 (11genes) out of 25 rice gene tagged markers (GTMs) in groundnut accounted for 68% transferability. The analysis of transferability of rice GTMs at individual peanut genotype level revealed a range of 79.17% to 91.67%. This confirmed the possibility of use of the rice markers/genes in groundnut.

Acceptability of Rhizoma Peanut Forage by Horses and Its Benefits on Feeding Behavior

Rhizoma peanut hay has been demonstrated to benefit horses’ feeding behavior with reduced inactive time, which can result in lower risk for abnormal behaviors in stabled horses. This publication is intended to provide information to Extension agents, horse owners, and equine facility managers. Written by C. Vasco, J. Dubeux, E. Santos, C. Wickens, and L. Warren, and published by the UF/IFAS Department of Animal Sciences, October 2023.

Short-term perennial peanut integration into bahiagrass system influence on soil microbial-mediated nitrogen cycling activities and microbial co-occurrence networks

Integration of perennial peanuts into warm-season grasslands offers a potential solution to reduce nitrogen (N) fertilizer input and enhance N cycling through soil microbial activities. There is limited information on the changes in soil microbial diversity and communities following the short-term integration of rhizoma perennial peanut (RPP; Arachis glabrata Benth.) into warm-season perennial bahiagrass (Paspalum notatum Flüggé) as well as its impact on N cycling processes. This study investigated changes in N cycling populations and soil microbial communities in bahiagrass-RPP mixtures compared to their monocultures at <2 years after RPP establishment in Spring (March) and Fall (October) seasons. Real-time qPCR was used to quantity N functional groups in the soil involved in nitrification, denitrification, and N2 fixation. DNA amplicon sequencing was employed to examine co-occurrence networks of soil microbes, while activities of soil enzymes [N-Acetyl-β-d-glucosaminidase (NAG) and leucine aminopeptidase (LAP)] involved in N mineralization were also measured. Bahiagrass-RPP mixtures had no effect on N cycling genes. Ammonia oxidizing archaea were the major ammonia oxidizing prokaryotes compared to ammonia oxidizing bacteria in bahiagrass-RPP systems. We found that bahiagrass-RPP mixtures exhibited greater prokaryotic alpha diversity and NAG activities than RPP monoculture. Meanwhile, RPP influenced soil fungal community composition (beta diversity) and enhanced the relative abundance of dominant soil fungal genera (Fusarium, Gibberella, and Humicola). The presence of RPP in bahiagrass systems led to increased negative microbial interactions in microbial occurrence networks. Greater complexities in microbial networks were linked to forage growth season, which was related to enrichment of the relative abundance of Basidiomycota. Our findings showed that RPP has the potential to influence N cycling process in bahiagrass system by altering the abundance of certain N cycling microbes, especially fungal taxa, within 2 years of RPP establishment.

Ornamental Rhizoma Peanut: Perceptions and Use by Florida Consumers

Ornamental rhizoma peanut (Arachis glabrata Benth.; ORP) is a low-maintenance groundcover for use in urban and residential landscapes. Despite its availability since 2002, consumer insights on ORP have never been assessed. Online surveys are readily accepted by academic researchers as a valuable research tool. An online survey was distributed to 5820 Floridians with the objective to assess the use and perceptions of ORP by consumers. A total of 907 survey responses were received. Most respondents identified themselves as home gardeners (89%), white (93%), female (75%), and over age 65 (60%). Out of several turfgrass alternative benefits, respondents most valued reducing herbicide/pesticide and fertilizer/water usage and preventing weed establishment (χ2 = 204, df = 6, P &lt; 0.001). The ORP selection purchased by respondents was predominately unknown. Most preferred ORP to flower heavily and frequently and maintain a canopy height below 20 cm in the landscape with infrequent mowing. Survey data show there is a potentially large consumer demand for ORP in Florida, but product availability, branding, and consumer access and engagement with information sources require additional focus in the coming years.

Arachis species: High‐quality forage crops—nutritional properties and breeding strategies to expand their utilization and feeding value

AbstractPlants of the genus Arachis originated from South America and are cultivated worldwide. The genus Arachis contains 83 species and nine intrageneric taxonomic sections. The cultivated peanut (Arachis hypogaea L.) belongs to the Arachis section, the forage peanut (Arachis pintoi Krapov. &amp; W. C. Greg.) belongs to the Caulorrhizae section, and the perennial peanut (Arachis glabrata Benth.) belongs to the Rhizomatosae section. These three peanut species have been developed for use as fodder crops. This review summarizes the forage value of Arachis species. Forage and perennial peanuts can be intercropped with forage species to feed livestock. The cultivated peanut vines and peanut by‐products, such as peanut skins and peanut meal, are also high‐quality fodder used to feed sheep, cattle, and poultry. A major limiting factor in terms of adopting forage and perennial peanuts as forage crops is their limited resistance to frosts, resulting from their low winter hardiness. Therefore, the feeding value of cultivated peanuts is higher compared to forage and perennial peanuts. This review suggests that Arachis is a suitable forage crop, focusing on their nutritional properties and breeding to increase their performance under cultivation and feeding value.

Soil Bacterial Communities Across Seven Rhizoma Peanut Cultivars (Arachis glabrata Benth.) Respond to Seasonal Variation.

Soil microorganisms play key roles in soil nutrient transformations and have a notable effect on plant growth and health. Different plant genotypes can shape soil microbial patterns via the secretion of root exudates and volatiles, but it is uncertain how a difference in soil microorganisms induced by crop cultivars will respond to short-term seasonal variations. A field experiment was conducted to assess the changes in soil bacterial communities of seven rhizoma peanut (Arachis glabrata Benth, RP) cultivars across two growing seasons, April (Spring season) and October (Fall season). Soils' bacterial communities were targeted using 16S rRNA gene amplicon sequencing. Bacterial community diversity and taxonomic composition among rhizoma peanut cultivars were significantly affected by seasons, cultivars, and their interactions (p < 0.05). Alpha diversity, as estimated by the OTU richness and Simpson index, was around onefold decrease in October than in April across most of the RP cultivars, while the soils from Arblick and Latitude had around one time higher alpha diversity in both seasons compared with other cultivars. Beta diversity differed significantly in April (R = 0.073, p < 0.01) and October (R = 0.084, p < 0.01) across seven cultivars. Bacterial dominant taxa (at phylum and genus level) were strongly affected by seasons and varied towards more dominant groups that have functional potentials involved in nutrient cycling from April to October. A large shift in water availability induced by season variations in addition to host cultivar's effects can explain the observed patterns in diversity, composition, and co-occurrence of bacterial taxa. Overall, our results demonstrate an overriding effect of short-term seasonal variations on soil bacterial communities associated with different crop cultivars. The findings suggest that season-induced shifts in environmental conditions could exert stronger impacts on soil microorganisms than the finer-scale rhizosphere effect from crop cultivars, and consequently influence largely microbe-mediated soil processes and crop health in agricultural ecosystems.

90 Fecal and blood biomarkers of metabolic status in horses fed rhizoma peanut hay

Rhizoma peanut (RP, Arachis glabrata) is an alternative to alfalfa (ALF, Medicago sativa L.) with less nonstructural carbohydrates (NSC) and crude protein. Yet, health variables in response to feeding RP have not been evaluated. This study investigated fecal and blood health markers in horses fed forage-only diets of ‘Florigraze’ RP, ‘Legendary XHD’ alfalfa, or ‘Coastal’ bermudagrass (BMG, Cynodon dactylon L.) hays. Six mature, healthy Quarter Horse geldings (593 kg ± SD 40) were fed the 3 hays in a replicated 3 × 3 Latin square with 3 21-d periods each separated by a 4-d washout. Hays were fed at 2% BW with ad libitum water and mineral supplement to meet maintenance requirements. Crude protein was 22, 16, and 8% and NSC was 11, 10, and 7.8% in ALF, RP, and BMG, respectively. On d 19 fecal and blood samples were collected immediately before (0 h) and 2, 4, and 8 h after feeding. Data were compared using mixed model ANOVA with repeated measures. Fecal dry matter, lactate, and pH averaged (±SEM) 19 ± 0.73%, 2.08 ± 0.172 mM, and 7.3 ± 0.05, respectively and did not differ by hay type. Fecal ammonia-nitrogen was greatest (P = 0.02) when fed ALF, but similar between RP and BMG. Fecal total short-chain fatty acids (SCFA) did not differ among hays (P = 0.07). Expressed as molar proportion, hay type did not alter acetate proportion (P = 0.12) but affected proportions of propionate (P = 0.02), butyrate (P = 0.04), andbranched-chain (BC) SCFA (isobutyrate + isovalerate + 2-methylbutyrate). Propionate proportion was greater (P = 0.02) when fed ALF than RP, but similar to both legumes when fed BMG. Butyrate proportion was greater (P = 0.04) for BMG-fed horses than RP-fed horses, while ALF was similar to both. Molar proportion of BC-SCFA was similar for both legume hays and least (P = 0.02) for BMG. Except for dry matter and lactate, time post feeding did not affect any of the fecal variables. Fecal dry matter decreased (P < 0.01) at 2 h and 4 h post feeding and had returned to pre-feeding values at 8 h post feeding. Fecal lactate decreased (P < 0.01) only at 8 h post feeding. Alfalfa resulted in glycemic (P = 0.01) and insulinemic (P = 0.01) responses greater than BMG, whereas the responses to RP were similar to those observed for ALF and BMG. Serum glucose was affected by time (P = 0.01) where it was elevated at 4 h post feeding. Insulin response was not affected by time post feeding (P = 0.70). Rhizoma peanut resulted in plasma urea nitrogen (PUN) lesser than ALF and similar to BMG. Levels of PUN decreased (P < 0.01) 8 h post feeding. Feeding rhizoma peanut provides more favorable metabolic responses than alfalfa, while still providing a high-quality source of nutrition.

Changes in soil microbial diversity and community composition across bahiagrass and rhizoma peanut pastures

Changes in soil microbial diversity and community composition across bahiagrass and rhizoma peanut pastures

Methane emissions and 13C composition from beef steers consuming binary C3-C4 diets.

Improvements in forage nutritive value can reduce methane emission intensity in grazing ruminants. This study was designed to evaluate how the legume rhizoma peanut (Arachis glabrata; RP) inclusion into bahiagrass (Paspalum notatum) hay diets would affect intake and CH4 production in beef steers. We also assessed the potential to estimate the proportion of RP contribution to CH4 emissions using δ13C from enteric CH4. Twenty-five Angus-crossbred steers were randomly allocated to one of five treatments (five steers per treatment blocked by bodyweight): 1) 100% bahiagrass hay (0%RP); 2) 25% RP hay + 75% bahiagrass hay (25%RP); 3) 50% RP hay + 50% bahiagrass hay (50%RP); 4) 75% RP hay + 25% bahiagrass hay (75%RP); 5) 100% RP hay (100%RP). The study was laid out using a randomized complete block design, and the statistical model included fixed effect of treatment, and random effect of block. Methane emissions were collected using sulfur hexafluoride (SF6) technique, and apparent total tract digestibility was estimated utilizing indigestible neutral detergent fiber as an internal marker. A two-pool mixing model was used to predict diet source utilizing CH4 δ13C. Inclusion of RP did not affect intake or CH4 production (P > 0.05). Methane production per animal averaged 250 g CH4/d and 33 g CH4/kg dry matter intake, across treatments. The CH4 δ13C were -55.5, -60.3, -63.25, -63.35, and -68.7 for 0%RP, 25%RP, 50%RP, 75%RP, and 100%RP, respectively, falling within the reported ranges for C3 or C4 forage diets. Moreover, there was a quadratic effect (P = 0.04) on the CH4 δ13C, becoming more depleted (e.g., more negative) as the diet proportion of RP hay increased, appearing to plateau at 75%RP. Regression between predicted and observed proportions of RP in bahiagrass hay diets based on δ13C from CH4 indicate δ13C to be useful (Adj. R2 = 0.89) for predicting the contribution of RP in C3-C4 binary diets. Data from this study indicate that, while CH4 production may not always be reduced with legume inclusion into C4 hay diets, the δ13C technique is indeed useful for tracking the effect of dietary sources on CH4 emissions.

Genomic relationships of the polyploid rhizoma peanut (Arachis glabrata Benth.) inferred by genomic in situ hybridization (GISH)

The rhizoma peanut (Arachis glabrata Benth., section Rhizomatosae) is a tetraploid perennial legume. Although several A. glabrata cultivars have been developed as forage and ornamental turf, the origin and genomic constitution of this species are still unknown. In this study, we evaluated the affinity between the genomes of A. glabrata and the probable diploid donors of the sections Rhizomatosae, Arachis, Erectoides and Procumbentes by genomic in situ hybridization (GISH). Single GISH analyses detected that species of the sections Erectoides (E2 subgenome) and Procumbentes (E3 subgenome) were the diploid species with the highest degree of genomic affinity with A. glabrata. Based on single GISH experiments and DNA sequence similarity, three species -A. duranensis, A. paraguariensis subsp. capibarensis, and A. rigonii-, which showed the most uniform and brightest hybridization patterns and lowest genetic distance, were selected as probes for double GISH experiments. Double GISH experiments showed that A. glabrata is constituted by four identical or very similar chromosome complements. In these assays, A. paraguariensis subsp. capibarensis showed the highest brightness onto A. glabrata chromosomes. Thus, our results support the autopolyploid origin of A. glabrata and show that the species with E2 subgenome are the most probable ancestors of this polyploid legume forage.

Legume proportion affects bahiagrass–rhizoma peanut mixture production and nutritive value and legume composition of cattle diets

Our objectives were to (1) quantify the effects of legume proportion on herbage accumulation (HA) and nutritive value of pasture mixtures compared with grass monocultures receiving typical or no N fertilizer application and (2) compare animal selection measures in legume–grass mixed pastures using microhistological and δ13C techniques applied to fecal samples. We evaluated HA and nutritive value in 2 grazing systems: (1) mixtures of Florigraze rhizoma peanut (Arachis glabrata Benth.) and Pensacola bahiagrass (Paspalum notatum Flügge) (MIX-SYS; 6 to 78% legume, grazed to a 15-cm stubble height at 42-d grazing intervals and ~7-d residence periods) and (2) bahiagrass monocultures receiving no N or 50 kg of N/ha per year (BG-SYS and BGN-SYS, grazed to 10-cm stubble height at 21-d grazing intervals with ~7-d residence periods) over 2 yr. Animal [~220 kg, 12-mo-old Brahman (Bos indicus) × Angus (Bos taurus) heifers] diet selection in MIX-SYS was quantified using microhistological and δ13C techniques applied to fecal samples. Herbage in vitro digestible OM (IVDOM) and CP concentrations increased linearly with increasing legume proportion in MIX-SYS up to ~45%, but MIX-SYS HA decreased linearly with increasing legume proportion. Treatment MIX-SYS had greater average HA [5,920 ± 271 (SE) kg/ha vs. 4,890 ± 236 kg/ ha for monocultures] and nutritive value than BG-SYS and BGN-SYS (CP of 12.9 ± 0.7% and IVDOM of 55.8 ± 1.0% for MIX-SYS vs. 9.1 ± 0.4% and 50.7 ± 1.5%, respectively, for monocultures). Results of microhistological and δ13C techniques applied to fecal samples were highly and positively correlated with sward canopy legume proportion, but fecal δ13C tracked legume proportion in the pasture more closely than the microhistological technique. Benefits of legumes to HA and nutritive value were observed at low legume participation, but they did not increase proportionally as legume percentage increased above ~45%. These results support a conclusion that relatively small proportions of legumes have measurable positive effects on important grassland characteristics.

Stable isotopes of C and N differ in their ability to reconstruct diets of cattle fed C3–C4 forage diets

Stable isotopes are useful for estimating livestock diet selection. The objective was to compare δ13C and δ15N to estimate diet proportion of C3–C4 forages when steers (Bos spp.) were fed quantities of rhizoma peanut (Arachisglabrata; RP; C3) and bahiagrass (Paspalumnotatum; C4).Treatments were proportions of RP with bahiagrass hay: 100% bahiagrass (0%RP); 25% RP + 75% bahiagrass (25%RP); 50% RP + 50% bahiagrass (50%RP); 75% RP + 25% bahiagrass (75%RP); and 100% RP (100% RP). Feces, plasma, red blood cell (RBC), and hair were collected at 8-days intervals, for 32 days. Two-pool mixing model was utilized to back-calculate the proportion of RP based on the sample and forage δ13C or δ15N. Feces showed changes using δ13C by 8 days, and adj. R2 between predicted and observed RP proportion was 0.81 by 8 days. Plasma, hair, and RBC required beyond 32-days to reach equilibrium, therefore were not useful predictors of diet composition during the study. Diets were best represented using fecal δ13C at both 8-days and 32-days. By 32-days, fecal δ15N showed promise (R2 = 0.71) for predicting diet composition in C3–C4 diets. Further studies are warranted to further corroborate fecal δ15N as a predictor of diet composition in cattle.

Composition and decomposition of rhizoma peanut (Arachis glabrata Benth.) belowground biomass

Roots and rhizomes can play an important role in nutrient cycling, however, few studies have investigated how their decomposition pattern is affected by defoliation and time of the year. This 2-year study evaluated root-rhizome composition and decomposition of a warm-season rhizomatous perennial legume [rhizoma peanut (RP; Arachis glabrata Benth.)] under continuous stocking or when defoliated by clipping every 56 days. A 168-days incubation trial was performed to determine disappearance of biomass and N and changes in acid detergent fiber (ADF), acid detergent insoluble N (ADIN), and C:N ratio. Additionally, three 56-days incubations were performed each year to evaluate the disappearance coefficient (B0) and relative decay rate (k). There were no treatment differences in any response for the 168-days incubation. After 168 days, 21 and 60% of initial biomass and initial N remained, respectively. Relative decay rate for OM and N were 0.0088 and 0.0035 g g−1 day−1, respectively. Carbon-to-N ratio decreased from 29 at day 0 to 17 at day 168. Concentration of ADIN increased from 6.9 to 19.3 g kg−1, plateauing at day 79. The B0 and k for remaining OM and N were greater in late than early season and could be explained by greater N concentration and lesser C:N ratio. Rapid decomposition, difference in C:N ratio from day 0 to 168, and the increase in ADIN concentration during incubation indicate large amounts of root-rhizome-soluble C at initiation of incubation. These data indicate that RP root-rhizome turnover is more responsive to season than defoliation frequency.