Mixed Pasture Research Articles

PSIX-2 Potential role of rumen microbiota in altering average daily gain and feed efficiency in meat goats fed simple and mixed pastures using bacterial tag-encoded FLX amplicon pyrosequencing

Abstract Our objective was to examine whether the comparative abundance of the Bacteroidetes (B) and Firmicutes (F) bacterial phyla in meat goats fed simple and mixed forages influenced average daily gain (ADG), rumen fermentation parameters and bacterial diversity changes using a tag-encoded FLX amplicon pyrosequencing (bTEFAP). Thirty-six Kiko-cross growing meat goats (BW = 27.7 ± 2.83) at approximate age of 7 mo were used in this study. Animals were randomly allocated to three pasture treatment groups (n = 12) as follows: (1) bermudagrass (BG; Cynodon dactylon), (2) sun hemp (SH; Crotalaria juncea) forage, and (3) BG + SH forage combinations for 45-d. Results indicated that there were no differences in initial BW among treatments, but final BW and ADG were higher (P < 0.01) for SH and BG + SH combinations than for BG alone. We investigated the alterations between the different forage diets and found that ADG and rumen fermentation (A/P ratio), were highly correlated with the abundance of various bacterial populations within the rumen microbiome. There were linear decreases in percentage of Bacteroidetes (R2 = -0.84; P < 0.05) associated with decreasing ADG. In contrast, increased ADG was linearly associated with higher percentages of Firmicutes (R2 = 0.79; P < 0.05), F/B ratio (R2 = 0.88; P = 0.07), total VFA (R2 = 0.45; P < 0.05), and lower A/P ratio (R2 = -0.72; P < 0.01). This suggest that the substrate and bacterial community have the role in adapting host biological parameters in meat goats. The abundance examination of both Bacteroidetes and Firmicutes will be useful for exploring the structure of gut microbiota as an estimate of animal performance.

Inferring mating system parameters in forage peanut, Arachis pintoi, for Brazilian Amazon conditions

ABSTRACT The search for alternatives to increase productivity and sustainability of livestock production in the Amazon region without increasing deforestation is challenging. Mixed pastures of grasses with forage peanut (Arachis pintoi) have shown positive economic impacts. However, gaps in the knowledge of the reproductive biology of A. pintoi have limited the development of new cultivars adapted to the environmental variations in the Brazilian Amazon. Pasture consortiums of Brachiaria humidicola with forage peanuts (cv. Mandobi) resulted in a 42% increase in weight gain productivity. New cultivars better adapted to the Amazon climate should bring even greater gains. We evaluated the mating system in twenty A. pintoi accessions, and approximately 40 offspring per accession genotyped with eight microsatellites (or markers). The parameters of genetic diversity and inbreeding, the outcrossing rate and coancestry were calculated. The observed heterozygosity was significantly higher and the fixation index was significantly lower in adults compared with the offspring. The crossing rate was variable among genotypes (2 to 80%), and the mean outcrossing rate was 36%. These results indicate that pollinator presence in pastures can influence gene flow in A. pintoi more than expected. Arachis pintoi presented a mixed mating system with a predominance of selfing, and families presented inbreeding and different levels of relatedness. New strategies of genotype conservation are needed to avoid pollinator-mediated crossing between accessions.

A regional analysis on the amphibian and reptile communities from the Carpathian Mountains and the abiotic factors that shape their distributions and community assemblages

Understanding how climate and land cover currently shape species distributions and community structure is crucial to inform conservation decisions. Unfortunately, limited information is available for the relative importance of climatic and land use variables in determining the distribution of amphibians and reptiles. Here, we studied amphibian and reptile communities from the Carpathian Mountains, asking (i) to what extent is the distribution of reptiles and amphibians determined by environmental gradients, (ii) does the response to these factors differ between amphibians and reptiles, and (iii) are reptile and amphibian communities at higher altitudes more similar to each other than communities from lower altitudes. We found that forests, pastures, and heterogeneous arable land best explain the composition of the herpetofauna, with mountain communities associated with coniferous forests, and lowland species with mixed or broad-leaved forests and pastures. Our results also suggest that reptiles and amphibians respond idiosyncratically to the influence of climate and land use. Reptiles responded more to land use and less to climate variables compared with amphibians. Of the three amphibian hybrids registered, one (Bombina) was associated with heterogeneous arable land. These results have potential implications for future conservation planning, especially in the light of global climate change and changes in land use. Hence, local and regional processes are important in shaping amphibian and reptile communities.

Sampling methods for clover species in grazed pastures to diagnose mineral deficiencies

Diagnosis of clover nutrient status is important for legume-based pasture systems. The protocols for sample collection and setting of nutrient guidelines are ill-defined. This research quantified how nutrient concentrations differed between laminae (leaflets) and petioles (leaf stems) of subterranean (sub) clover (Trifolium subterraneum) and white clover (T. repens) as a first step in developing appropriate sampling procedures to examine the nutrient status of clover species. Field samples of sub and white clovers from three pasture sites in the Wairarapa and Canterbury were separated into lamina and full petiole and chemically analysed for nitrogen (N), phosphorus (P), potassium (K) and sulphur (S). Lamina + petiole K concentrations were lower in sub clover (2.3%) than white clover (3.2%). Across both species, the lamina concentrations of N (4.9%), P (0.36%) and S (0.28%) were higher than in the petiole (1.8%, 0.29% and 0.12% respectively) but the reverse was found for K (1.8 % lamina, 3.7% petiole). As a consequence, increasing the proportion of petiole added with the lamina affected the nutrient concentration of lamina + petiole samples so that N, P and S% declined but K% increased. In a subset of samples, NIR analysis found the crude protein of lamina + petiole in white clover was 24% compared with 21% in sub clover. Clover laminae of both species had 33% crude protein compared with only 11% in the petiole. The diagnosis of clover nutrient status for fertiliser recommendations should be based on lamina-only samples. In contrast, mixed pasture samples for nutritive value analysis should include clover laminae and petioles, plus grass and herb pasture components, to simulate grazing intake by livestock. The lack of defined sampling protocols may explain some of the difficulties previously reported in herbage nutrient interpretation and reconciling soil test results.

Metabolism of carbohydrates in Estilosantes cv. Campo Grande under different systems of cultivation and nitrogen fertilization

The objective of this study was to verify the activity of invertases in Estilosantes under the influence of cultivation systems and nitrogen fertilization in two seasons. The experiment was conducted in the Xaraés area, where Estilosantes was planted according to a 2 x 2 factorial scheme with two cultivation systems (monoculture and mixed pasture) in the absence or presence of fertilization (75 kg of N ha-1). A randomized block design with four replications was used. The neutral cytosol (Inv-N), vacuole acid (Inv-V) and cell wall acid (Inv-CW) invertase activity and reducing sugar contents in the leaves and stems were evaluated and analyzed by a 5% probability F-test. The interaction between cultivation systems and nitrogen fertilization was significant for Inv-N in the leaves in the summer, such that greater activity occurred in response to the mixed pasture system and nitrogen fertilization. Nitrogen increased the activity of the Inv-N in the stem in both periods, increased the activity of Inv-V in the leaf in the summer, and decreased the activity of Inv-CW in the fall. This cultivation system influenced the activity of Inv-N regardless of the period of the year and did not interfere with the activities of the acid invertases. The invertases did not show regular changes in relation to nitrogen fertilization.

ARTHROPOD DIVERSITY LOSS DUE TO MONOCULTURE PRACTICE IN SOUTH LAMPUNG, INDONESIA

It has been widely known that animal biodiversity is higher in ‘more natural’ environment than agricultural system. Arthropod is one of phyla in animalia kingdom which member includes 90% of identifiable animal species and their diversity can act as bioindicator of environment health. The objective of this study is to compare arthropod diversity in mixed plantation, pasture, and monoculture plantation in South Lampung, Indonesia. Forty pitfall traps were set at 1 m interval in each area. Mixed plantation has the highest diversity index and the lowest dominance. Our result suggested that land-use change from natural environment, which is reflected by mixed plantation, into pasture and monoculture plantation has reduced arthropod diversity in South Lampung.

Microsymbionts of forage peanut under different soil and climate conditions belong to a specific group of Bradyrhizobium strains

The use of mixed pastures of grasses with forage peanut (Arachis pintoi) is growing and offers promising results. This leguminous forage plant has a stoloniferous growth habit and tolerates more intense defoliation and shading. However, there are few studies on its symbiosis with nitrogen (N2) fixing bacteria and no studies on genetic identification of its native microsymbionts. The aim of this study was to evaluate phenotypic and genetic diversity and the symbiotic efficiency of bacterial strains isolated from nodules of forage peanut intercropped with grasses in pasture areas. Root nodules were collected from the Belomonte cultivar in Itabela, Bahia, and BRS Mandobi cultivar in Lavras, Minas Gerais, Brazil. The areas of sample collection had contrasting physical and chemical characteristics. Samples of 10 plants per area and 5 nodules per plant were taken. The strains isolated from the nodules were analyzed for culture characteristics (growth period and change in pH of the culture medium), their 16S rRNA, gyrB and nifH genes were partially sequenced, and authentication and analysis of symbiotic efficiency in forage peanut plants were carried out. Both the authentication and symbiotic efficiency experiments were carried out in a greenhouse under axenic conditions, using A. pintoi cv. BRS Mandobi in a completely randomized design with four replications. Authentication was performed in long neck bottles (500 mL) filled with nutrient solution, and symbiotic efficiency was performed in polypropylene seedling plug pots containing a mixture of sand and vermiculite with a nutrient solution. A total of 74 bacterial strains were obtained from isolation of the forage peanut nodules, 40 from Itabela, and 34 from Lavras. Partial sequencing of the 16S rRNA gene was obtained for 48 strains, 30 from Itabela, and 18 from Lavras. The strains isolated from nodules of forage peanut in pasture areas of Itabela, were identified in the following genera: Bradyrhizobium (21), Rhizobium (5), Burkholderia (2), Kocuria (1), and Paenibacillus (1). The strains coming from soils of Lavras, were identified in the following genera: Bradyrhizobium (13), Rhizobium (2), Burkholderia (1), Mucilaginibacter (1), and Enterobacter (1). In the authentication experiment, 17 strains from Itabela, and 13 strains from Lavras, exhibited nodulation. From these authenticated strains, 18 were identified by 16S rRNA sequencing as belonging to the Bradyrhizobium genus. Of these strains, 11 from the two areas exhibited high symbiotic efficiency in A. pintoi, and their results were better than those of the strains currently approved as inoculants for this crop. The non-nodulating strains are probably nodule endophytes. Sequencing of the gyrB housekeeping gene, performed in 13 strains, confirms phylogenetic groups of potential new species among the strains isolated from A. pintoi, which include strains able to nodulate this species, belonging to a specific phylogenetic group of Bradyrhizobium. Sequences of nifH gene of efficient strains belonged to a group different from that formed by non-nodulating strains.

Animal performance in grass monoculture or silvopastures using tree legumes

Silvopasture systems using tree legumes have potential to reduce C footprint of livestock systems in the tropics. This 4-year study evaluated productive responses of signal grass (Brachiaria decumbens Stapf.) and the performance of cattle in silvopastoral systems (SPS) in the sub-humid tropical region of Brazil. The experimental design was randomized complete block with three replications. Treatments were: signal grass + Mimosa caesalpiniifolia Benth.; signal grass + Gliricidia sepium (Jacq.); and signal grass monoculture. Cattle were managed under continuous stocking with variable stocking rate. Herbage mass (HM) was greater on signal grass monoculture (5057 kg DM/ha) than in mixed pastures (3292 kg DM/ha, average). There was interaction (P < 0.05) between treatment × evaluation month for HM, and the greatest value was observed in May (2722 kg DM/ha). Herbage allowance varied from 1.29 to 3.07 kg DM per kg of body weight (BW). Herbage accumulation rate varied throughout the evaluations, with the greatest rate observed in July (56 kg DM/ha per day) and the lowest in December (15 kg DM/ha per day). Average daily gain was similar across systems (0.65 kg day−1), varying according to month. Stocking rate ranged from 1.5 animal units (AU; equivalent of a 450-kg animal) per ha in December (dry season) to 2.2 AU/ha in July (rainy season). Animal performance per area tended to decrease in the SPS (411 kg BW ha−1 year−1) when compared with signal grass in monoculture (508 kg BW ha−1 year−1), especially in the Mimosa system. Adding tree legumes reduced animal performance per area due to competition between arboreal and herbaceous components, especially in the Mimosa system that had a more closed canopy.

Effect of alternating total mixed ration and pasture feeding on the fatty acid content and health indices of Jersey and Fleckvieh x Jersey milk

Certain fatty acids (FAs), such as omega-3 and conjugated linoleic acid (CLA) are considered essential FAs with beneficial health effects for humans. Milk is considered a relatively inexpensive and readily available source of these FAs and is part of a recommended healthy daily diet. The aim of the study was to determine the effect of diet changes on the FA composition of Jersey (J) and Fleckvieh x Jersey (FxJ) milk. Cows were alternately put on kikuyu-ryegrass pasture, followed by a feedlot system, then returned to kikuyu-ryegrass pasture for four weeks each. The same concentrate mixture was fed to cows regardless of feeding system. The feedlot system consisted of a partial total mixed ration (pTMR). Milk samples were collected two and four weeks after diet changes and stored at −20 °C until laboratory analysis by gas chromatography. The FA concentration of milk was not affected by breed, although it was affected significantly by diet changes. Most notably, the total omega-3 and -6 FAs decreased when cows were fed pTMR while increasing when the diet was changed back to pasture feeding. The CLA content of milk was similarly affected. That is, concentrations decreased significantly when the cows were on the pTMR diet and increased when cows were put back on the pasture-based diet. The results suggested that the health benefits of milk fat are affected negatively when cows are fed pTMR compared with being fed in a pasture-based system. The health benefits of milk are reduced owing to decreased levels of the CLA content of milk fat. Therefore, feeding additional hay in a pasture-based production system should be reconsidered when aiming to produce milk that provides health beneficial qualities. Keywords: breed, diet, n-3 fatty acid, n-6 fatty acid, pasture, Fleckvieh

Potential role of rumen microbiota in altering average daily gain and feed efficiency in meat goats fed simple and mixed pastures using bacterial tag-encoded FLX amplicon pyrosequencing1.

Cost-effective and feasible production system of meat goats requires that grazed forages are converted to profitable goat meat product. However, there are studies as how altering forage type influences ruminal fermentation parameters and animal growth performance, and interact with microbiota in meat goats. Our objective for current study was to examine whether the comparative abundance of the Bacteroidetes (B) and Firmicutes (F) bacterial phyla in meat goats fed simple and mixed forages influenced average daily gain (ADG) and rumen fermentation parameters. In the present study, a molecular approach, bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP) was applied to accomplish diversity analyses of rumen bacterial populations. Thirty-six Kiko-cross growing meat goats (body weight (BW) = 27.7 ± 2.83 kg) at approximately 7 mo of age were used in this study. Animals were randomly allocated to 3 pasture treatment groups (n = 12) as follows: 1) bermudagrass pasture (BG; Cynodon dactylon), 2) sunn hemp forage (SH; Crotalaria juncea), and 3) BG + SH forage combinations. There were 2 replicates per treatment and animals grazed these pastures for 45 d. Results indicated that treatments had similar initial BW, but final BW and ADG were higher (P < 0.01) for SH and BG + SH combinations than for BG alone. Animal ADG and rumen fermentation (acetate to propionate; A/P ratios) were highly correlated with the abundance of various bacterial populations within the rumen microbiome. There were linear decreases in percentage of Bacteroidetes (R2 = -0.84; P < 0.05) associated with decreasing ADG. In contrast, increased ADG was linearly associated with higher percentages of Firmicutes (R2 = 0.79; P < 0.05), F/B ratios (R2 = 0.88; P = 0.07), total VFA (R2 = 0.45; P < 0.05), and lower A/P ratio (R2 = -0.72; P < 0.01). This suggests that the substrates (diets) and bacterial community have the role in adapting host biological parameters in meat goats. The abundance examination of both Bacteroidetes and Firmicutes will be useful for exploring the structure of gut microbiota as an estimate of animal performance.

Increasing the population of forage peanut in a mixed pasture by controlling the canopy height

AbstractThe aim of this study was to determine a temporary strategy for increasing the legume population in an established pasture of brachiaria grass (Brachiaria brizantha) and forage peanut (Arachis pintoi). The treatments comprised four previous long‐term canopy heights (10, 20, 30 and 40 cm) from the establishment (the first 32 months after treatment initiation). From September 2014, all of the experimental units were kept at 10 cm height. The pastures were evaluated for their forage harvest, forage mass, botanical composition and stolon and tiller density. The tiller density and brachiaria grass mass were maintained in all pastures since the first season of evaluation (p &gt; 0.10). The stolon density and legume mass were initially lesser at 30 and 40 cm than those at 10 and 20 cm, early in the experiment, but progressively increased over time. After 1 year under 10 cm height, the population and mass of legume were similar in all treatments. Therefore, reducing the canopy height to 10 cm at the beginning of the rainy season is an efficient method to increase the botanical composition of forage peanut in mixed pastures with brachiaria grass.

Improved management increases carrying capacity of Brazilian pastures

Grazing pasture without appropriate soil conservation and animal management often leads to reduced soil quality and decreased productivity because of trampling induced compaction. Our objective was to evaluate the effect of three conservation-based pasture management strategies on soil physical attributes. The treatments were (1) Brachiaria decumbens + mineral-N fertilization, (2) mixed pasture + legume (forage peanut, Arachis pintoi), and (3) Brachiaria without fertilization were compared with a native grassland reference area without management. The hypothesis is that nitrogen fertilization favors an increase in the animal stocking rate, maintaining the physical quality of the soil. The treatments had no significant effect on soil porosity, bulk density, or water retention. The S-index showed that intense animal trampling in the treatment with nitrogen fertilization resulted in the most intense degradation. Mixed pasture with the intercropped legume and N-fertilization maintained soil physical quality similar to the area without management, reinforcing the importance of appropriate soil management practices in pasture. However, although the N-fertilized area had soil physical quality similar to the others, it could support more animals, suggesting an economic advantage over other soil management practices. To preserve or enhance soil physical quality, mixed pastures and fertilization can be adopted, increasing the soil load-bearing capacity, which represents more animals per area.

Effect of Increasing Species Diversity and Grazing Management on Pasture Productivity, Animal Performance, and Soil Carbon Sequestration of Re-Established Pasture in Canadian Prairie.

Simple SummaryCanadian grasslands are recognized for providing high quality forage for grazing livestock and wildlife. The study was conducted on a re-established pasture in a Western Canadian semi-arid climate to investigate the effect of pasture species mixture and grazing management on pasture productivity, animal performance, and soil carbon sequestration. Pasture productivity and animal response were independent of pasture mixture but affected by grazing management. Average pasture dry matter productivity was greater with deferred-rotational grazing while pasture quality and animal gain were higher with continuous grazing. Soil carbon change varied with pasture seed mixture and grazing management interaction where pasture with 7-species mixture under continuous grazing had the lowest soil carbon gain. The objective of the study was to determine the effect of type of pasture mix and grazing management on pasture productivity, animal response and soil organic carbon (SOC) level. Pasture was established in 2001 on 16 paddocks of 2.1 ha that had been primarily in wheat and summer fallow. Treatments consisted of a completely randomized experimental design with two replicates: two pasture mixes (7-species (7-mix) and 12-species (12-mix)) and two grazing systems (continuous grazing (CG) and deferred-rotational grazing (DRG)). Pasture was stocked with commercial yearling Angus steers (Bos Taurus, 354 ± 13 kg) between 2005 and 2014. All pastures were grazed to an average utilization rate of 50% (40% to 60%). Average peak and pre-grazing pasture dry matter (DM) yield and animal response were independent of pasture seed mixture but varied with grazing management and production year. Average peak DM yield was 26.4% higher (p = 0.0003) for pasture under DRG relative to CG (1301 kg ha−1). However, total digestible nutrient for pasture under DRG was 4% lower (p < 0.0001) as compared to CG (60.2%). Average daily weight gain was 18% higher (p = 0.017) for CG than DRG (0.81 kg d−1), likely related to higher pasture quality under CG. Soil carbon sequestration was affected by seed mixture × grazing system interaction (p ≤ 0.004). Over the fourteen years of production, pasture with 7-mix under CG had the lowest (p < 0.01) average SOC stock at 15 cm (24.5 Mg ha−1) and 30 cm depth (42.3 Mg ha−1). Overall, the results from our study implied that increasing species diversity for pasture managed under CG may increase SOC gain while improving animal productivity.

Characterization of the rumen and fecal microbiome in bloated and non-bloated cattle grazing alfalfa pastures and subjected to bloat prevention strategies

Frothy bloat is an often fatal digestive disorder of cattle grazing alfalfa pastures. The aim of this study was to investigate ruminal and fecal microbiota dynamics associated with development of alfalfa-induced frothy bloat and to further explore how bloat prevention strategies influence the composition of these microbial communities. In a 3 × 3 crossover experiment, twelve rumen-cannulated steers were sequentially subjected to: (1) pure alfalfa pasture, (2) pure alfalfa pasture supplemented with the pluronic detergent ALFASURE, and (3) alfalfa – sainfoin mixed pasture. Eleven out of 12 steers in pure alfalfa pasture developed clinical bloat, whereas ALFASURE treatment prevented the development of bloat in all 12 steers and alfalfa – sainfoin prevented bloat in 5 out of 11 steers. Development of bloat was associated with considerable shifts in the microbiota profile of rumen contents. In particular, the microbiota of solid rumen contents from bloated steers contained higher species richness and diversity. Streptococcus, Succinivibrio and unclassified Myxococcales were enriched in the rumen microbiota of bloated steers, whereas Fibrobacter and Ruminococcus were overrepresented in the rumen contents of non-bloated steers. Our results provide novel insights into bloat-associated shifts in the composition and predicted functional properties of the rumen microbiota of cattle grazing alfalfa pasture.

Productivity and crude protein concentration of Tifton 85 pasture-based mixed with pinto peanut

ABSTRACT Mixed pasture grass-legume systems balance forage supply and minimize environmental impacts by reducing the need for nitrogen fertilization. Pinto peanut (Arachis pintoi Krap. and Greg. “Amarillo”) has several traits that are suitable for mixed pastures but have not yet been adequately explored. The aim of this study was to evaluate a mixture of Tifton 85 bermudagrass (Cynodon dactylon) and pinto peanut and evaluate forage yield, crude protein, and stocking density. A two-year study of three grazing systems was used with the following treatment combinations: (a) Tifton 85 (T) + 100 kg N ha-1 yr-1 + pinto peanut (T + PP+100); (b) T + 100 kg N ha-1 yr-1 (T + 100; control, pure grass); and (c) T + 200 kg N ha-1 yr-1 (T + 200; positive control, pure grass). In this study, forage yield, pasture characteristics and responses of lactating cows were evaluated. The experimental design was completely randomized with three treatments (grazing systems), three replicates (paddocks), and repeated measures (grazing cycles within seasons). Forage accumulation, crude protein concentration, and stocking rate were 15.1; 11.3 and 14.1 t DM ha-1 yr-1; 17%, 16%, and 17%; and 5.3; 4.9 and 6.1 AU ha-1 day-1, respectively. The grass-legume system yielded the best results.

Productivity and nutritive value of elephant grass pastures under organic and conventional production systems.

Elephant grass (EG) (Pennisetum purpureum Schum.) have great importance in tropical and subtropical climates, especially on dairy farms. Normally, EG is established alone under high fertilization levels. EG in organic production system can improve low production costs and environmental issues, are still little known. The aim of this research was to evaluate the performance of herbage yield, nutritive value, extraction/ export nutrient and forage yield and animal responses. Three production systems of EG were analyzed: (i) EG mixed spontaneous-growing species (SGE) in warm-season and ryegrass (R) in cool-season under organic production; (ii) EG mixed SGE + R under conventional system (positive control); and (iii) EG based under conventional production (control). Holstein cows were used in a rotational stocking. Forage samples were collected to evaluate the pasture and animal responses. Seven grazing cycles were performed during the experimental period (312 days). Herbage yield, forage intake, and stocking rate were 12548; 10270; 19168 kg ha-1 and 2.5; 2.6; 2.7% and 3.3; 2.1; 4.5 AU ha-1 day-1, respectively. Crude protein of EG was 17.9; 15.4; 16.4%, respectively. Mixed pastures, in conventional and organic production, had a better forage distribution throughout the seasons. Highest forage yield and extraction/ export nutrient was reported in pure EG within the conventional system.

Prospects for improving perennial legume persistence in mixed grazed pastures of south-eastern Australia, with particular reference to white clover

This review examines the prospect of improving perennial legume adaptation to grazed mixed pasture swards across the higher-altitude regions of south-eastern Australia through improved management, particularly as it relates to soil fertility. The range of adapted perennial species available to farmers often remains limited to only one perennial forage legume species, white clover (Trifolium repens L.). Despite recent advances in cultivars for increased persistence in dryland environments, white clover remains sensitive to drought with its inherently shallow root system and limited capacity to restrict water loss from herbage. With few alternative species likely to become widely available in the foreseeable future, prospects for extending the boundaries of perennial legume adaptation likely rely on a dual approach of improving soil fertility and further genetic improvement in white clover. Improved soil fertility would focus on overcoming soil acidity and addressing nutrient deficiencies, particularly of phosphorus, potassium, boron and molybdenum, which tend to be more widespread in the target region. Addressing these soil constraints would alleviate periodic moisture stress by: (1) increased water availability through improved infiltration and soil hydraulic properties; (2) increased root growth to maximise exploration of the soil volume; and (3) better maintenance of plant cell structures to foster improved osmotic regulation. However, the extent to which white clover adaption may be extended remains an issue of further research. This review highlights an opportunity for further genetic improvement of white clover by focusing on improving the capacity to recover from periodic droughts through seedling regeneration. Further breeding efforts in white clover should examine the feasibility of selecting for hard seed characteristics more similar to the best-adapted subterranean clover (Trifolium subterraneum L.) cultivars across this region to promote ongoing seedling regeneration.

Dry matter and nutritive value responses of native, naturalised and sown pasture species to soil Olsen P

The soil phosphorus (P) requirements of 18 species that included native grasses and naturalised legumes were compared with the predominant sown species (Trifolium subterraneum, Lolium perenne and Phalaris aquatica) in a series of glasshouse and field experiments based on the Long-term Phosphate Experiment at Hamilton, Victoria. The native grasses Austrostipa scabra and Rytidosperma caespitosum had the lowest external P requirements, as measured by the Olsen P at which 90% of maximal dry matter (DM) production was obtained, but were of low nutrient value as livestock feed. The naturalised legume Lotus corniculatus had the lowest external P requirement of the legumes, but had low DM production. The highest legume DM production under low-P conditions in the field and one glasshouse experiment was obtained for T. subterraneum. This was attributed to its large seed, which enables rapid initial growth and thus captures light and nutrient resources early in the growing season. However, it forms a relatively low proportion of the pasture sward in low-P soil under grazed mixed pasture conditions in the field. This was attributed to its relatively high nutritive value, which leads to it being preferentially grazed, leaving species that are either less palatable or less accessible to grazing livestock. This work suggests that, in low-P environments, there is a much stronger selection pressure favouring low relative palatability over P efficiency. In conclusion, to maintain desirable species in temperate low-input pastures, sufficient P needs to be applied to maintain fertility above a threshold at which the less-palatable species begin to invade.

PSXI-29 Dynamics of litter decomposition in signalgrass and forage peanut mixed pastures.

PSXI-29 Dynamics of litter decomposition in signalgrass and forage peanut mixed pastures.

Changes in soil nitrogen stocks following vegetation restoration in a typical karst catchment

AbstractSoil nitrogen (N) accumulation enhances carbon (C) sequestration and subsequently the restoration of degraded ecosystems, but the changes in soil N properties after vegetation restoration in such ecosystems are poorly understood. We collected data from 358 fixed points in the karst catchment in China to determine the trends, magnitude, and mechanisms of soil N sequestration after 10 years of revegetation. The revegetation types were tillage fields that were abandoned or were converted to pasture, planted forest, or converted to mixed pasture and forest and pasture lands that were abandoned (P_Aban) or converted to mixed pasture and forest (P_Mix). The changes in soil N density (g m−2) over time were insignificant, and only P_Aban, P_ Mix, and the overall catchment experienced significant increases in soil N concentration (g kg−1). Structural equation modeling indicated that bedrock exposure affected the change in soil N concentration (∆NC) and the soil N sequestration value (∆ND) via affecting the change in soil C concentration, by directly affecting bulk density, soil depth, and Ca2+. The soil C:N ratio increased significantly, and the increase in soil N was slower than that of C, suggesting a decoupling of soil C and N accumulation in the initial stage of revegetation. ∆ND was significantly related to the change in soil C:N ratio, indicating that the coupling between soil C and N may be constrained by insufficient soil N sequestration during revegetation. These findings suggest that the restoration of degraded karst ecosystems requires an increase in soil N input early during vegetation restoration.