Grass-legume Pastures Research Articles

Influence of erosion and deposition on carbon and nitrogen accumulation in resampled steepland soils under pasture in New Zealand

Although erosion occurs under pastures in New Zealand North Island hill country, previous work shows that the soils on mid-slopes (>19°) have large and significant average gains of soil carbon (C) and nitrogen (N) over a period of about 30years. Both sheetwash erosion (from patches of bare soil) and soil deposition (from upslope) could have occurred in the intervening 30years, and this could have led to a loss or gain of soil C. The fission-derived radionuclide 137Cs is a unique tracer for studying erosion and sedimentation because it is strongly adsorbed onto soil particles, and its movement in the environment is predominantly due to physical processes. We hypothesized that accumulation and loss of 137Cs and C would be correlated if erosion and deposition processes were responsible for the observed changes in soil C. We therefore measured 137Cs in archived samples, previously used to assess changes in C and N, together with 137Cs in the re-sampled soil horizons, to an average depth of 37cm. The data show that, on average, there has been a small gain in total profile 137Cs over this time, and complex patterns within individual soil profiles over 30years. There was only a weak correlation between 137Cs and C accumulation above 15cm soil depth, but, in contrast, a much stronger relationship was found below 15cm. A possible explanation for the observed pattern is soil thickening due to deposition, but the deposition may occur with variable 137Cs contents. Generally deposition does not account for all of the increase in C, and regression analysis between Cs and C for all layers suggested that erosion/deposition accounted for 20–30% of the total change in C. In a detailed case study, the sampling of erosion scars caused by landslides showed that soil C stocks (0–20cm) can increase from 10 to 80 tonne (Mg) C ha−1 within 70years. Use of the CENTURY model indicated that input of N from legumes in the pasture enabled N and C to accumulate in the surface soil. This suggests that gains in soil C and N under hill country pasture that occur in these facets of the landscape are probably largely due to the ongoing input from C and N in the grass-legume pastures rather than erosion or deposition of soil.

Emisión de metano entérico en rumiantes en pastoreo

Esta revisión explora el conocimiento asociado a los aspectos que determinan la emisión de metano en rumiantes en pastoreo. Se aborda el efecto de la especie forrajera, variedades dentro de especies y asociaciones gramínea/leguminosa, además de aspectos de manejo de la pastura como su madurez, carga animal, sistema de pastoreo y nivel de fertilización. El análisis hace énfasis en las influencias en las emisiones por unidad de materia seca consumida. Existen diferencias entre especies forrajeras en la emisión de metano que están asociadas a diferencias en las concentraciones de fibra, a variaciones en la tasa de paso y la presencia de metabolitos secundarios. Mayores concentraciones de fibra reducen las tasas de paso, el consumo de materia seca y aumenta la producción de metano por unidad de materia seca consumida. El efecto de la inclusión de leguminosas sobre la producción de metano es variable y esta influenciado por la presencia de metabolitos secundarios como los taninos y las saponinas. Los resultados de los trabajos revisados sugieren que existen oportunidades para reducir las emisiones de metano por unidad de materia seca consumida cuando las prácticas de manejo de las pasturas aumenten las tasas de paso y el consumo voluntario. Además el aumento en el consumo conllevaría a la reducción de emisiones de metano por unidad de producto animal.

Midwest Cropping System Effects on Soil Properties and on a Soil Quality Index

Cropping systems may improve or decrease soil quality depending on the specific crop rotation, nutrient amendments, and tillage practices employed. We conducted this study to determine the effect of six cropping systems in the Wisconsin Integrated Cropping Systems Trial on soil properties after 18 yr of continuous treatments. We sampled soils (0–5 cm and 5–20 cm depths) following the corn (Zea mays L.) year of three grain‐based systems (continuous corn and two grain rotations), after both corn and alfalfa (Medicago sativa L.) in two forage‐based systems (organic and conventional), and in grass–legume pasture. Extractable P and K, pH, total organic carbon (TOC), total N, active soil C, potentially mineralizable nitrogen (PMN), water‐stable aggregates (WSA), bulk density (BD), penetrometer resistance, and total microbial biomass (TMB) were measured, and the Soil Management Assessment Framework (SMAF) soil quality index (SQI) was determined. The pasture (0–5 cm) was significantly better than all other systems in almost all soil quality indicators and had the highest SQI (96 vs. mean of 87 for others). The alfalfa‐based systems had more total N, TOC, active C, PMN, and WSA and higher BD in one or both depths than did the grain‐based systems but SQIs were not different. Among the grain systems, there was less variation and few significant differences were observed. While there were significant differences among systems for most soil properties, a SQI based on a composite of seven soil properties, showed few differences on this well managed, productive, prairie‐derived soil.

Effect of rumen-undegradable protein supplementation and fresh forage composition on nitrogen utilization of dairy ewes

Previous trials with dairy ewes fed stored feeds indicate a positive effect of rumen-undegradable protein (RUP) supplementation on milk yield. However, dairy sheep production in the United States is primarily based on grazing mixed grass-legume pastures, which contain a high proportion of rumen-degradable protein. Two trials were conducted to evaluate the effects of high-RUP protein supplementation and fresh forage composition on milk yield and N utilization of lactating dairy ewes fed in confinement or on pasture. In a cut-and-carry trial, 16 multiparous dairy ewes in mid-lactation were randomly assigned to 8 pens of 2 ewes each. Pens were randomly assigned 1 of 2 protein supplementation treatments, receiving either 0.0 or 0.3kg of a high-RUP protein supplement (Soy Pass, LignoTech USA Inc., Rothschild, WI) per day. Within supplementation treatment, pens were randomly assigned to 1 of 4 forage treatments, which were applied in a 4 × 4 Latin square design for 10-d periods. Forage treatments included the following percentages of orchardgrass:alfalfa dry matter: 25:75, 50:50, 75:25, and 100:0. No interactions were observed between supplement and forage treatments. Supplementation with a high-RUP source tended to increase milk yield by 9%. Milk yield, milk protein yield, milk urea N, and urinary urea N excretion increased linearly with increased percentage of alfalfa. Milk N efficiency was greatest on the 100% orchardgrass diet. In a grazing trial, 12 multiparous dairy ewes in mid lactation were randomly assigned to 3 groups of 4 ewes each. Within group, 2 ewes were randomly assigned to receive either 0.0 or 0.3kg of a high-RUP protein supplement (SoyPlus, West Central Cooperative, Ralston, IA) per day. Grazing treatments were arranged in a 3 × 3 Latin square design and applied to groups for 10-d periods. Ewes grazed paddocks that contained the following percentages of surface area of pure stands of orchardgrass:alfalfa: 50:50, 75:25, and 100:0. No interactions were found between supplement and forage treatments. Milk yield, milk protein yield, and milk urea N increased linearly with increased percentage of alfalfa in the paddock. In conclusion, supplementing with high-RUP protein tended to increase milk yield and increasing the proportion of alfalfa in the diet increased dry matter intake, milk yield, and protein yield of lactating dairy ewes fed or grazing fresh forage.

Improving the accuracy of digestibility estimates for cattle grazing tropical pastures when sampling with oesophageal fistulated cattle

The in vitro digestibility analysis of extrusa samples collected from oesophageal fistulated cattle is widely used to estimate the digestibility of diets selected by resident grazing cattle. In the present study, oesophageal fistulated steers were used to sample a range of grass–legume pastures continuously stocked with small herds of resident cattle at two sites in northern Queensland at different times of the year. Pepsin–cellulase in vitro analysis was used to measure in vitro dry matter loss (IVDML) during incubation. Additional laboratory analyses were used to demonstrate that unless appropriate corrections are applied, serious inaccuracies can occur in the estimates of in vivo digestibility as a result of (1) differences between IVDML of extrusa (feed plus saliva) and the IVDML of the feed consumed (feed without saliva), (2) differences in the botanical and chemical composition between the extrusa samples and the diets of the resident cattle, and (3) differences between grasses and legumes in the linear-regression relationships used to estimate in vivo digestibility from IVDML. Methodologies to minimise such errors are described and results illustrating the magnitude of potential errors are presented. In the dataset from the present study, it was clear that differences between extrusa and resident diets in grass–legume proportions consumed were the major cause of error but other causes of error were also important. Appropriate methodologies to improve accuracy are recommended.

Near Infrared Reflectance Spectroscopy (NIRS) for determination of chemical entities of natural pasture from Ethiopia

In the mixed crop-livestock farming system of Ethiopia, natural pasture production is related to seasonal rainfall distribution which is restricted to only a few months of the year. Livestock owners in this country experience periods of excess forage in the rain season where preserving it through haymaking became tradition as a strategy for the periods of scarcity, particularly the dry season of a year. Forage can also be stored as standing hay, the cheapest way of conserving forage, in a place like pastoral and agro-pastoral production system where a decline in quality can be tolerated. Mixed grass-legume pasture samples from different agro-ecology were collected and portion of the samples were analyzed conventionally to determine their chemical composition (dry matter, ash, crude protein, neutral detergent fiber, acid detergent fiber, lignin) and in vitro dry matter digestibility to validate the NIRS calibration. NIRS was evaluated by the coefficient of determination in calibration (R 2 ), standard error of calibration (SEC), and standard error of cross validation (SECV). The results showed NIRS is extremely useful for predicting nutrient contents as compared to conventional chemical analysis methods which are not difficult to conduct, but they are expensive in terms of time and resources.

Yield and botanical composition of a mixed grass-legume pasture in response to maintenance fertilization

This study was carried out on a low-productive Brachiaria brizantha cv. Marandu pasture, mixed with Arachis pintoi cv. Belmonte (forage peanut), established 13 years ago in a Red-Yellow Latosol in Acre State, western Brazilian Amazon. The purpose was to evaluate the response of this pasture to different fertilizer combinations, aiming at identifying the nutritional factors responsible for the fall of pasture carrying capacity and for the reduced vigor of forage peanut. It was used a randomized complete block design, with three replications and 12 combinations of nitrogen, phosphorus, potassium, lime, sulfur, and micronutrients (100 kg/ha of N, P2O5 and K2O; 300 kg/ha of dolomitic lime; 30 kg/ha of sulfur and FTE BR-10). Fertilizers were broadcast in 5 × 5-m plots, and the experimental area was isolated from grazing for 35 days. Pasture response to fertilizations showed that nitrogen was the main limiting nutrient to forage production. The other nutrients, applied singly or in a combined way, without nitrogen source, did not change dry matter accumulation rate. Overall, fertilizations with nitrogen provided dry matter accumulation rate of 115 kg/ha/day in comparison to only 32 kg/ha/day when nitrogen was not applied. There was no response from forage peanut to fertilization, so, there are other factors responsible for its reduced vigor of regrowth.

Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 42:65-78 (2010) - DOI: https://doi.org/10.3354/cr00863 Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures M. P. Perring1,4,*, B. R. Cullen2, I. R. Johnson3, M. J. Hovenden1 1School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia 2Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria 3010, Australia 3IMJ Consultants, Armidale, New South Wales 2350, Australia 4Present address: Ecosystem Restoration Lab, School of Plant Biology (M090), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia *Email: michael.perring@uwa.edu.au ABSTRACT: Native perennial grass and sown grass-legume pastures are an important agricultural and environmental resource. We investigated the impact of rising carbon dioxide concentration ([CO2]) and projected climate changes on these pasture ecosystems in southeastern Tasmania, Australia, using a biophysical simulation model, EcoMod. The model consists of interdependent modules that describe soil physicochemical and hydrological characteristics, and pasture growth and senescence, with fluxes described by empirical and mechanistic equations. Our simulations showed that in native pastures, projected climate change increased the biomass of C4 grasses, with limited impact upon C3 grasses, a trend reversed by rising [CO2]. In sown pastures, projected climate change decreased the biomass of perennial rye grass Lolium perenne and total biomass markedly by 2070, whilst subterranean clover Trifolium subterraneum biomass increased. Subterranean clover biomass changed little with increased [CO2] alone, whereas perennial rye grass biomass increased. Responses across pastures reflected species’ tolerances to environmental factors, with projected climate change generally having more of an impact on biomass than rising [CO2]. Changes in both [CO2] and climate led to a reduction in protein content and digestibility. Soil inorganic nutrient concentrations decreased with increasing [CO2] and increased with projected climate change. Further simulations should investigate whether these patterns are robust for different sites and alternative environmental futures. Our results reinforce the need to pursue adaptation strategies in response to environmental change in order to maintain productive pasture ecosystems. KEY WORDS: Lolium perenne · Ecosystem model · Simulation · Nutrient availability · Productivity · Tasmania Full text in pdf format PreviousNextCite this article as: Perring MP, Cullen BR, Johnson IR, Hovenden MJ (2010) Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures. Clim Res 42:65-78. https://doi.org/10.3354/cr00863Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 42, No. 1. Online publication date: June 03, 2010 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2010 Inter-Research.

Spatial distribution of livestock concentration areas and soil nutrients in pastures

Livestock concentration areas can be significant point sources of nutrient pollution. Our objective was to determine the spatial distribution of livestock concentration areas in pastures at the farm scale, along with the distribution of soil nutrients at the individual livestock concentration area scale. We georeferenced and measured the size of all livestock concentration areas in cool-season grass-legume pastures on five farms (four grazing dairies and a beef cattle farm) in Maryland, Pennsylvania, and New York during two years. Soil of selected concentration areas on each of the farms was sampled to 0 to 5 and 0 to 15 cm (0 to 2 and 0 to 6 in) depths to compare nutrient levels with paired unaffected areas of the pasture. On one farm, we sampled two concentration areas more densely (20 to 25 samples, 0 to 5 cm depth along each of five 100 m [328 ft] transects) to measure spatial distribution of soil nutrients. The transects were arranged radially to encompass variation both up and downslope. We installed runoff plots at three locations on and near the two concentration areas to measure nutrients in surface water runoff from simulated rainfall. On the five farms, concentration areas occurred most frequently at paddock gates (38% of sites). Although fewer in number, concentration areas at feeding sites were often larger than those at gates or other locations and accounted for most (48%) of the area affected by livestock congregation. Most concentration areas were small (median area 100 m² [1,076 ft²]), isolated (median distance, 61 m [200 ft] from a water body), and surrounded by vegetation. Intensive sampling on one farm showed that soil within 20 to 40 m (66 to 132 ft) of concentration areas was enriched in phosphorus, which contributed to higher phosphorus concentration in the runoff from simulated rainfall compared with the rest of the pasture. Pastures used as holding and feeding areas with highly elevated soil nutrients and no surrounding vegetation to filter runoff represented a direct threat to surface water quality. Many concentration areas, however, were surrounded by vegetation, which would mitigate this risk.

Properties and suggested management strategies for some well drained maize producing soils of north-western Nigeria

Some well drained maize growing soils of the northwest Agricultural Zone of Nigeria were characterized, classified and management strategies proffered for them. The soils were moderately deep to deep (65 - 150 cm), well drained and well structured, yellowish brown (10YR 5/4, 5/8) to yellowish red (5YR 4/6, 4/8) loams. Soil reaction ranged from very strongly acid to neutral (pH 5.0 - 6.8). Exchangeable Ca (< 2 cmol kg-1) and K (< 0.15 cmol kg-1), organic carbon (< 10 g kg-1), total N (< 1.5 g kg-1), P (< 10 mg kg-1) and Cu (< 1mg kg-1) were low, while exchangeable Mg (0.3-1.0 cmol+ kg-1), CEC (6-12 cmol+ kg-1) and available Zn (> 1 mg kg-1) were medium. The CEC values of the soils show that they are not suitable for continuous cultivation but would require a high ratio of fallow or grass-legume pasture to crops. This option should, therefore, be followed in their management. Should they be used for continuous cultivation, soil OM levels must be raised to ≥ 20 g kg-1 (≥ 15 g kg-1) soil, by applying FYM and animal dung. This strategy would raise CEC, buffering capacity and base saturation and improve soil structure and water and nutrient retention capabilities.

Action learning in partnership with Landcare and catchment management groups to support increased pasture sowings in southern inland Queensland

The incorporation of sown pastures as short-term rotations into the cropping systems of northern Australia has been slow. The inherent chemical fertility and physical stability of the predominant vertisol soils across the region enabled farmers to grow crops for decades without nitrogen fertiliser, and precluded the evolution of a crop–pasture rotation culture. However, as less fertile and less physically stable soils were cropped for extended periods, farmers began to use contemporary farming and sown pasture technologies to rebuild and maintain their soils. This has typically involved sowing long-term grass and grass–legume pastures on the more marginal cropping soils of the region. In partnership with the catchment management authority, the Queensland Murray–Darling Committee (QMDC) and Landcare, a pasture extension process using the LeyGrain™ package was implemented in 2006 within two Grain &amp; Graze projects in the Maranoa-Balonne and Border Rivers catchments in southern inland Queensland. The specific objectives were to increase the area sown to high quality pasture and to gain production and environmental benefits (particularly groundcover) through improving the skills of producers in pasture species selection, their understanding and management of risk during pasture establishment, and in managing pastures and the feed base better. The catalyst for increasing pasture sowings was a QMDC subsidy scheme for increasing groundcover on old cropping land. In recognising a need to enhance pasture knowledge and skills to implement this scheme, the QMDC and Landcare producer groups sought the involvement of, and set specific targets for, the LeyGrain workshop process. This is a highly interactive action learning process that built on the existing knowledge and skills of the producers. Thirty-four workshops were held with more than 200 producers in 26 existing groups and with private agronomists. An evaluation process assessed the impact of the workshops on the learning and skill development by participants, their commitment to practice change, and their future intent to sow pastures. The results across both project catchments were highly correlated. There was strong agreement by producers (&gt;90%) that the workshops had improved knowledge and skills regarding the adaptation of pasture species to soils and climates, enabling a better selection at the paddock level. Additional strong impacts were in changing the attitudes of producers to all aspects of pasture establishment, and the relative species composition of mixtures. Producers made a strong commitment to practice change, particularly in managing pasture as a specialist crop at establishment to minimise risk, and in the better selection and management of improved pasture species (particularly legumes and the use of fertiliser). Producers have made a commitment to increase pasture sowings by 80% in the next 5 years, with fourteen producers in one group alone having committed to sow an additional 4893 ha of pasture in 2007–08 under the QMDC subsidy scheme. The success of the project was attributed to the partnership between QMDC and Landcare groups who set individual workshop targets with LeyGrain presenters, the interactive engagement processes within the workshops themselves, and the follow-up provided by the LeyGrain team for on-farm activities.

Manipulating dietary preference to improve animal performance

This paper reviews opportunities to improve the diet quality, intake and performance of animals through manipulation of the partial preference commonly shown by grazing animals for different pasture components. Using evidence from the well-worked example of grass–legume pastures, potential opportunities to manipulate preference are highlighted, including: (i) altering plant characteristics to change the relative preference of alternative species or cultivars; (ii) utilising variation in preference among and within animal species; and (iii) working with, rather than against, known preference patterns, by offering forages as spatially separated monocultures within the same paddock or at different times of the day. In all cases, it is argued that is important to consider the full complexities of pasture–animal interactions, in particular, how current diet choices feed back to determine choices available subsequently in the pasture. To develop feeding systems where desirable pasture traits for animal performance are sustained at a high abundance in the diet, plant and animal breeding selection practises and grazing management systems should take greater account of the existence of partial preferences.

Alternative Methods of Estimating Forage Height and Sward Capacitance in Pastures Can Be Cross Calibrated

Alternative Methods of Estimating Forage Height and Sward Capacitance in Pastures Can Be Cross Calibrated

Chemical variations in the biostructures produced by soil ecosystem engineers. Examples from the neotropical savannas

“Ecosystem engineers” are those organisms capable to modify physically the environment by producing “biogenic” structures (BS). Termites, earthworms, ants and other large macroinvertebrates produce BS with varying properties. In this study, our objective was to quantify total C org (g per kg dry soil), N H 4 + and N O 3 - concentrations (μg per g dry soil) in different parts of the BS produced by termites and ants to test the hypothesis that higher concentrations are found where new building material is deposited, i.e. at the top of the BS. The study was carried out in a natural savanna (NS), an introduced grass-legume pasture (IP) and a gallery forest (GF) at the Carimagua Research Station in the Eastern Plains of Colombia. Progressive sampling distances across the BS were used, i.e. from the top to the base of the BS by using proportional distances, i.e. 20–100% for large BS and 50–100% for the smallest BS, and these were compared with two types of control soil, 120% or 150% in the case of large and small BS, respectively, and soil sampled 1 m away from the BS. All the BS analysed had, in general, higher concentrations of nutrients than the control soil. There were differences in the variables measured in the BS according to the organism that produced them. The lowest values of C org were observed in the BS (surface dumps) deposited by fungus-growing ants ( Trachymyrmex sp. in the NS, and Atta laevigata in the GF), while the highest concentrations were found in the BS produced by termites in the GF, where a high N concentration was also observed. Nutrient concentrations were higher in general in the BS than in the control soil in all cases. However, other BS seemed not to have any influence in the surrounding soil. We concluded that the activity of soil ecosystem engineers increased the spatial variability of chemical parameters measured in this study. The ecological significance of these differences is discussed.

Stability of the spatio-temporal distribution and niche overlap in neotropical earthworm assemblages

The spatial distribution of soil invertebrates is aggregated with high-density patches alternating with low-density zones. A high degree of spatio-temporal organization generally exists with identified patches of specific species assemblages, in which species coexist according to assembly rules related to competitive mechanisms for spatial and trophic resources occur. However, these issues have seldom been addressed. The spatio-temporal structure of a native earthworm community in a natural savanna and a grass–legume pasture in the Colombian “Llanos” was studied during a 2-year-period. A spatially explicit sampling design (regular grid) was used to discern the distribution pattern of species assemblages in both systems. Earthworms were collected from small soil pits at three different sampling dates. Data collected from 1 m 2 soil monoliths were also used in the present study. Data were analyzed with the partial triadic analysis (PTA) and correlograms, while niche overlap was computed with the Pianka index. The PTA and correlogram analysis revealed that earthworm communities displayed a similar stable spatial structure in both systems during the 2-year study period. An alternation of population patches where different species' assemblages dominated was common to all sampling dates. The medium-sized Andiodrilus sp. and Glossodrilus sp. exhibited a clear spatial opposition in natural savanna and the grass–legume pasture for the duration of the study. The Pianka index showed a high degree of niche overlapping in several dimensions (vertical distribution, seasonality of population density) between both species. The inclusion of space-time data analysis tools as the PTA and the use of classical ecological indices (Pianka) in soil ecology studies may improve our knowledge of earthworm assemblages' dynamics.

Spatial dissociation between two endogeic earthworms in the Colombian “Llanos”

Although there has been a growing interest in the study of soil fauna spatial distribution during the past decade, the identification of the environmental driving factors behind the population patterning are difficult to highlight. Soil physico-chemical heterogeneity is partly responsible for structuring the population. However, the available statistical analyses show that the proportion of the population spatial variance that can be ascribed to soil habitat variability is modest. We studied the spatial distribution of two medium-sized endogeic earthworm species ( Andiodrilus sp. and Glossodrilus sp.) and the spatial segregation between them. The survey was undertaken in a native savanna and a grass-legume pasture in the Colombian “Llanos”. The presence of spatial dependence in the data (i.e. earthworm counts) was tested using two different approaches: the Spatial Analysis using Distance IndicEs (SADIE) analyses and cross-coregionalization. The SADIE index allowed for testing the spatial association or dissociation between earthworm counts. The spatial organization of both species was well structured in the natural savanna while they were randomly distributed in the pasture in almost all sampling dates. When the spatial distribution was different from randomness it was always aggregated irrespective of the land-use system. There was no absolute stable spatial pattern in the natural savanna although a general pattern seemed to emerge. On the contrary, no pattern was observed in the pasture. Both species displayed opposite spatial distributions ( P < 0.05) that were of different intensity depending on the sampling date. The presence of opposite patches and gaps suggests the presence of a competitive exclusion phenomenon (at least spatial) that deserves further investigations.

Integrating cattle into the slash-and-burn cycle on smallholdings in the Eastern Amazon, using grass-capoeira or grass-legume pastures

Abstract In the humid tropics of northern Brazil, where slash-and-burn cropping is the prevailing smallholder land use system, pastures ecologically degrade after 7–10 years of use, mostly due to invading vegetation, decline of soil fertility (N, P) and insect pests. Degraded pasture areas cannot be easily restored or returned to cropping, so large areas are abandoned. To avoid this degradation process, two alternative pastures were tested to incorporate cattle into the slash-and-burn cropping cycle. It was thought that the inclusion of secondary woody fallow vegetation, locally called capoeira, or of legumes in pastures restores the soil for a subsequent cropping phase while allowing an acceptable level of animal performance. This hypothesis was tested in a researcher-managed on-farm experiment in Igarape-Acu (Bragantina region, Para). A grass-legume pasture (GLP), combining the grass Brachiaria humidicola with three multi-purpose legumes, was compared with a pasture, where controlled regrowth of capoeira was tolerated (GCP), and tested against two controls in the form of a conventional B. humidicola pasture (GP) and undisturbed regrowth of capoeira (UC). The pastures were grazed in a rotational system for 2 years at 1.5 livestock units (LU) ha−1 in the first year and at 1.2 LU ha−1 in the following year. The results showed that the GCP kept the full regenerative potential of the capoeira, showing no significant loss of phytodiversity (GCP 67 species 100 m−2; UC 72 species 100 m−2) and low dissimilarity in species composition measured by Euclidian distance (UC/GCP = 51; UC/UC = 52; GCP/GCP = 33). On the GLP, the legumes Arachis pintoi and Cratylia argentea almost disappeared due to the grazing pressure, while Chamaecrista rotundifolia var. grandiflora was little palatable and invaded the plots by seed propagation. None of the legumes produced a meaningful quantity of nodules, and no difference in total soil N was found between GLP and the other pasture treatments. With regard to animal production, both alternative pastures were less productive than GP over 21 months of grazing (GLP = 384 kg liveweight ha−1, GCP = 474 kg ha−1, GP = 659 kg ha−1), which was attributed to overstocking in the second year. GCP was considered to be an interesting option for smallholdings, provided the balance between the vigorous regrowth of capoeira and forage grass cover can be maintained. In contrast, on GLP a more palatable Ch. rotundifolia accession would be desirable and the establishment of all legumes needs to be improved. It was concluded that GCP would support a subsequent cropping phase better than GLP. However, on both pastures stocking rates would have to be frequently adjusted a management practice that is of secondary consideration in a crop/livestock system in which cattle are kept as cash-generating assets.

Birdsfoot Trefoil, a Valuable Tannin-Containing Legume for Mixed Pastures

Introduction Legumes are important components of pastures. Legumes not only fix atmospheric nitrogen (N2) for their own use when properly inoculated, they provide nitrogen (N) for associated grasses and forbs. A range from 150 to 240 lb N per acre is needed to equal the contribution of legume N in legume-grass mixtures (14). Using a legume reduces the purchase and application costs of N fertilizer and may reduce soil acidification and N losses to the environment. Many legumes are deep-rooted and therefore more drought-tolerant than grasses. Under grazing, legumes are more commonly used as a component of mixtures with grasses than as monocultures. This is because fibrous-rooted grasses are valuable sources of soil organic matter, they provide better protection from soil erosion, are more resistant to grazing and treading damage than legumes, and well-managed grass-legume mixtures provide more-thanadequate levels of crude protein (CP) for highly productive livestock. Legumes have higher nutritive value and voluntary intake than grasses (18), and steer gains are higher on legume-grass mixtures than on N-fertilized grass monocultures (14). However, most legumes can cause bloat. In a uniform stand, a maximum of 50% bloat-causing legume is considered bloat-safe, but bloat has been reported in mixtures with less than 15% bloat-causing legume where selective grazing could occur (30). The low digestibility of tropical legumes has been attributed to their high tannin content (53). Well-managed temperate grass-legume pastures, however, can have excessive CP and therefore animal performance can benefit from the presence of moderate concentrations of condensed tannins that control bloat and decrease ammonia and methane production in the rumen while increasing rumen undegradable protein (58). There are several species in the genus Lotus that produce condensed tannins in high enough concentrations to influence herbage digestibility and animal performance. Big trefoil (Lotus uliginosus Schkur.) produces concentrations of tannins at levels high enough to be considered an antiquality component (2). In contrast, birdsfoot trefoil (L. corniculatus L.; BFT) has lower herbage tannin concentration, but levels can be high enough to be beneficial. This review will discuss agronomic aspects of BFT and assess studies that have compared the livestock production value of BFT with forages that contain little or no condensed tannin. Many studies of tannins in BFT have been carried out in New Zealand with sheep, but studies with cattle are included where available.

Temporal folate status during lactation in mares and growth in foals

To identify changes in folate status of mares and foals during lactation and growth, respectively. 20 Thoroughbred mares and foals. Pregnant mares, and following foaling the same mares with their foals, were maintained on mixed grass-legume pasture and fed either a traditional dietary supplement rich in sugar and starch (SS) or a dietary supplement high in fat and fiber (FF). Blood samples were collected monthly from mares and foals up to 6 months after foaling. Total folate concentration in feed and forage was determined. Analyses of plasma folate, RBC folate, plasma homocysteine (HCY), and milk folate concentrations were performed. Mare plasma folate concentrations declined moderately during 6 months of lactation. Mare RBC folate concentrations initially increased after foaling up to 3 months but declined toward the end of the study. Plasma HCY concentration was higher for mares fed the SS supplement, compared with mares fed the FF supplement from foaling to 6 months of lactation. Milk folate concentrations decreased during the first 3 months and then increased. Foal plasma folate initially declined but then increased. Stable concentrations of RBC folate were observed in foals. Plasma HCY concentrations in foals were unaffected by growth during the last 5 months. References range values for plasma folate, RBC folate, milk folate, and plasma HCY concentrations in healthy lactational mares and young growing foals were determined. Folate status was not impaired in lactating mares and growing foals under the conditions in our study. It appears that folate supplementation is not necessary.

Relationship Between Gross Nitrogen Cycling and Nitrous Oxide Emissionin Grass-clover Pasture

Replacement of high-input N fertilized pastures with low-input grass-legume pastures may provide a mitigation option to reduce agricultural N2O emissions. This study examined the relationship between N-cycling rates and N2O production and evolution from the root zone of grass-clover pastures of various ages (production year 1, 2 and 8). The experimental approach included cross-labelling pasture monoliths with 15N-enriched substrates to identify sources of N2O, in combination with assessment of gross N mineralization and nitrification. Nitrous oxide emissions were generally low, fluctuating between 82 and 136μg N2O–N m−2 d−1, independent of pasture age. The 15N labelling indicated that at least 50% of the N2O was derived from the soil NH 4 + pool, approaching 100% in June. In the two year old pasture the NH 4 + pool contributions to N2O emissions varied significantly with sampling time. Emission rates of N2O correlated positively with soil NH 4 + concentrations and the NH 4 + supply as expressed by gross mineralization. The N2O emissions showed a significant inverse relationship with soil NO 3 − , but was not correlated with the supply of NO 3 − as expressed by gross nitrification. The ratio N2O vs. nitrification averaged 0.05% (range 0.004 to 0.29%) and varied with sampling time showing the lowest value in wet soil conditions.