Annual Pasture Research Articles

Near real-time Feed On Offer (FOO) from MODIS for early season grazing management of Mediterranean annual pastures

Near real-time estimation of Feed On Offer (FOO) from Moderate Resolution Imaging Spectroradiometer (MODIS) data was developed to help farmers improve their grazing management during early growth of annual pastures to maximize grass utilization for wool production. Data were collected from 72 fields on 15 farms in southwestern Australia. From these data, an exponential relationship at the field scale between the Normalized Difference Vegetation Index (NDVI) estimated from MODIS and FOO data was derived for the vegetative growth phase for FOO between 0 and 2000 kg ha–1 (R 2 = 0.71–0.75). This relationship transformed the dimensionless index NDVI to a dimensioned (kg ha–1) measure of FOO, from which farmers could apply extension advice received from the Western Australian (WA) Department of Agriculture and Food Production (DAFP). Above an FOO of 2000 kg ha–1 or when the annual pasture species began to senesce, the relationship ceased to have predictive value. Near real-time estimates of FOO from MODIS proved useful to farmers despite an apparent standard error of ±300 kg ha–1. How to reduce the errors in FOO predicted from MODIS NDVI is also discussed.

The first genetic maps for subterranean clover (Trifolium subterraneum L.) and comparative genomics with T. pratense L. and Medicago truncatula Gaertn. to identify new molecular markers for breeding

This study reports on the construction of the first genetic maps of subterranean clover (Trifolium subterraneum L.), a diploid, inbreeding annual pasture legume, and alignment of its linkage groups with those of red clover (T. pratense L.) and Medicago truncatula Gaertn. Transferability of red and white clover (T. repens L.) simple sequence repeat (SSR) markers to subterranean clover was observed. A total of 343 SSR loci were mapped into eight subterranean clover linkage groups, with 6–31 loci per linkage group and 27 loci with similar locations between two distinct F2 mapping populations. Phenotypic data obtained for flowering time, content of three isoflavonoids (formononetin, genistein and biochanin A), hardseededness, leaf markings, calyx pigmentation and hairiness of stems were analyzed, together with genotypic data. Genomic intervals influencing each trait were assigned to one to three chromosome regions, accounting for 5.5–59.8% of the phenotypic variance. Syntenic relationships were observed among subterranean clover, red clover and Medicago truncatula genomes. Comparisons of loci shared between the three species indicated that at least two chromosomal regions have undergone duplications in the subterranean clover genome. Candidate genes for isoflavone content were identified using M. truncatula as a reference genome. Synteny-based segmentation observed in Brassicaceae chromosomes helped to account for the apparent segmental-based relationship between the clover genomes, particularly within the subterranean clover lines. The proposed segmental nature of clover genome could account for the extensive variation observed between the parental genotypes, while not preventing production of fertile intercrosses.

Simulation of soil organic carbon dynamics under different pasture managements using the RothC carbon model

Recently, soil carbon sequestration in agro-ecosystems has been attracting significant interest as soil organic carbon (SOC) can potentially offset some atmospheric carbon dioxide. The objectives of this study were to use the RothC model to simulate soil carbon sequestration and determine the proportion of pasture production as carbon input for SOC sequestration under different pasture types and pasture management in a long term experiment established in 1992. There were two types of pastures, annual and perennial pastures, with or without application of limestone. Simulation results showed that with an initial setting for the stubble retention factor of 0.65 and root/shoot ratio of 0.5 for annual pasture and 1.0 for perennial pasture, RothC can adequately simulate SOC for both pasture types, especially annual pasture. Using an inverse modelling technique, the root/shoot ratio was determined as 0.49 and 0.57 for annual pasture and 0.72 and 0.76 for perennial pasture with and without limestone application, respectively. There was a large improvement in model performance for perennial pasture with and without limestone application. The root mean squared errors (RMSE) reduced from 3.19 and 2.99 t C ha −1 in the initial settings to 2.09 and 2.10 t C ha −1, while performance efficiency (PE) increased from 0.89 and 0.91 to the same value of 0.95 when the root/shoot ratio of 0.72 and 0.76 were used for limed and unlimed perennial pastures. However, there was little improvement for annual pasture as RMSE had little change and PE was the same. As the stubble retention factor and root/shoot ratio can be combined into one factor that measures an equivalent amount of total above-ground pasture production allocated for soil carbon input, the modelled results can be summarised as 1.2 times and 1.4 times the above-ground dry matter for annual and for perennial pasture, respectively, regardless of liming. Our results provide useful information for simulation of soil carbon sequestration under continuous pasture systems.

Quantitative mapping of pasture biomass using satellite imagery

A knowledge of the amount of pasture biomass available in farm paddocks is crucial for improving utilization and productivity in the Australian grazing industry. A method to quantitatively map the biomass of annual pastures under grazing has been developed using the Normalized Difference Vegetation Index (NDVI) derived from high-resolution satellite imagery. Relationships between field-measured pasture biomass and the NDVI were examined for different transects in paddocks under different grazing regimes across three geographically dispersed farm sites. A significant linear relationship (R 2 = 0.84) was observed when the NDVI was regressed against biomass. The slope of the relationship between the NDVI and biomass declined in a highly predictable (R 2 = 0.82) exponential form as the growing season progressed and this pattern was consistent across four separate seasons. This knowledge was used to formulate a reliable model to predict paddock average pasture biomass using the NDVI. The model estimates were validated against observed biomass in the range 500–4000 kilograms of dry matter per hectare (kg DM ha–1) with R 2 = 0.85 and a standard error of 315 (kg DM ha–1).

Potential effects of animal management and genetic improvement on enteric methane emissions, emissions intensity and productivity of sheep enterprises at Cowra, Australia

The efficacy of technologies to reduce enteric CH4 emissions from ruminants are typically evaluated on individual animals with little consideration of enterprise scale impacts. While impacts of the many rumen manipulations being studied are hard to anticipate, there is adequate information to assess impacts of farm management changes and potential animal genetic changes on whole farm productivity and enteric CH4 emissions. Seven common sheep production systems grazing an annual pasture in central New South Wales, Australia, were modelled using GrassGro® (version 3.1.2). A range of animal management and animal genetic strategies were examined for their impact on total enteric emissions, emission intensity (i.e., kg CO2 equivalent/kg live weight (LW) of animal sold) and profit. Within enterprises, mitigation options were compared at their respective sustainable economic optimum stocking rate as it was assumed that farmers would seek to achieve the highest sustainable profit achievable from a finite land resource. Management options considered were choice of lambing time, mating ewes for the first time as lambs rather than yearlings, and feeding lambs to reduce time to slaughter. The potential for using selective animal breeding was also tested, with sheep physiological parameters being altered in GrassGro® to represent genetic improvement in fecundity, LW gain, residual feed intake and CH4 yield. In general, the management choices delivering lowest emission intensity were also the most profitable within sustainability constraints. Mating maiden ewes as lambs was only effective in reducing enterprise emissions intensity in self-replacing flocks (i.e., no purchased replacements). When stocking rates were at the sustainable economic optimum, choice of enterprise or management had little influence on total enteric emissions from the enterprise. If decisions are guided solely by economics, farmers are likely to continue with similar levels of production (and emissions) until a price on enteric CH4 emissions makes the sheep enterprise unprofitable, or an alternative more profitable enterprise than sheep grazing emerges. Improving animal genetics for residual feed intake or CH4 yield offers opportunity to reduce enterprise emissions, but industry progress toward higher genetic merit for these traits is expected to be slow due to relatively low heritability and competing economic imperatives for progress in other traits.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

European rabbit ( Oryctolagus cuniculus) engineering effects promote plant heterogeneity in Mediterranean dehesa pastures

Mammalian herbivores can have dramatic effects on the vegetation through different mechanisms, and may therefore modify resource distribution or create habitat for other species. Organisms that cause such changes are classified as ecosystem engineers. The European rabbit ( Oryctolagus cuniculus) is a semi-fossorial mammal native to the Iberian Peninsula and a keystone species in Mediterranean foodwebs. Rabbits are central-place foragers, but few studies have analysed their ecosystem engineering effects in the vicinity of warrens. Here, we explored the role of rabbits as ecosystem engineers in Mediterranean pastures in central Spain. We studied the spatial patterns and internal heterogeneity in the vegetation community of different spatial subunits created by rabbits (warrens, the warren influence area, and latrines). Within the different subunits, rabbit activities gave rise to patches and gradients with different plant species richness, diversity and height, and a high internal heterogeneity (dissimilarity) in floristic composition. Through different mechanisms, they have a significant effect on species coexistence and competitive interactions, and increase the number of available niches for plants which otherwise would not be able to establish. In conclusion, rabbits can act as allogenic ecosystem engineers in Mediterranean pastures, increasing heterogeneity and contributing to the high biodiversity of Mediterranean annual pastures.

Continuous vs. Rotational Grazing of Cool Season Pastures During the Summer Months

Continuous vs. Rotational Grazing of Cool Season Pastures During the Summer Months

Methane emissions from grazing Angus beef cows selected for divergent residual feed intake

Residual feed intake (RFI) is the difference between actual feed intake and expected feed intake required for maintenance and production, such as growth of beef cattle and milk production in dairy cattle. RFI has been shown to be linked with a reduction in CH4 emissions in studies that used grain based diets. Our study quantified CH4 emissions from 48 Angus cows selected based on estimated breeding values (EBV) for extremes in RFI. These EBV were based on a post weaning RFI test conducted at the Western Australian Department of Agriculture and Food Vasse Research Centre. Two groups of cows with divergent RFI were used being: 25 high RFI (i.e., HRFI, low efficiency) cows with an EBV of 0.68±0.220kg/d, and 23 low RFI (i.e., LRFI, high efficiency) cows with an EBV of −0.69±0.335kg/d. Methane emissions were measured under grazing conditions in a Western Australian annual pasture production system using the Open Path Fourier Transform Infrared Spectrophotometer (OP-FTIR) technique. A group average emission rate was obtained for the two RFI lines of cows. Each group was measured separately over a two 6d periods being in the summer when the cows were pregnant and grazing annual pastures of a low dry matter (DM) digestibility of 550g/kg, and in the winter when the cows were nursing calves and grazing annual pastures with a high DM digestibility of 810g/kg. It was hypothesised that LRFI cows would produce less CH4 when grazing both high and low quality pastures. When pregnant and grazing low quality pastures, both groups of cows produced similar amounts of CH4/day (0.26±0.013 versus 0.26±0.018g CH4/kg of liveweight (LW) for LRFI and HRFI cows respectively. While nursing calves and grazing high quality pastures, there was a difference (P<0.05) in daily CH4 emissions between the LRFI and HRFI cows of 0.34 CH4±0.017 versus 0.46±0.023g CH4/kg LW). The hypothesis that LRFI cows produce less CH4 is not supported by results for these cows grazing low quality summer pasture, but it is supported when grazing high quality winter pastures. Results indicate LRFI cattle may have the potential to contribute to reduced CH4 emissions under grazing systems when provided with a high nutritional quality pasture source.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T. A. McAllister, Section Guest Editor; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Impacts of future climate scenarios on the balance between productivity and total greenhouse gas emissions from pasture based dairy systems in south-eastern Australia

The challenge for agriculture is to increase production in warmer climates in order to meet the demands of an increasing global population, while also meeting targets for reduced greenhouse gas (GHG) emissions. Our aim was to quantify the net effect of future climate scenarios on the productivity and total GHG emissions from pasture based dairy systems in 4 regions of south-eastern Australia using the biophysical model DairyMod. In each region, a single paddock in the grazing rotation of a dairy farm was simulated. This paddock was grazed at a stocking density of 50 lactating dairy cows/ha for a period of one day each time the pasture biomass reached 2.2t dry matter (DM)/ha. In this way, the annual stocking rate (i.e., cows/ha) reflected the number of times that the paddock was grazed annually. No supplementary feed was offered to the animals. Model estimates of annual pasture intake, stocking rate, milk production, CH4 and N2O emissions were compared at each site in a baseline climate (1971–2000) and 3 future climate scenarios representing increasingly warm and dry conditions, termed the ‘2030’, ‘2070 mid’ and ‘2070 high’ scenarios. At Kyabram (northern Victoria) summer irrigated perennial pastures were modelled in the baseline scenario, with supplementary irrigated annual pasture systems simulated in the baseline scenario for comparison, and in the future scenarios. At Terang (south-western Victoria), Ellinbank (south-eastern Victoria) and Elliott (north-western Tasmania) dryland perennial pastures were modelled. In dryland systems, increased pasture intake, stocking rate and milk production was modelled in all future scenarios for the cool temperate climate at Elliott, with reduced production in the ‘2070 mid’ and ‘2070 high’ scenarios at Ellinbank and Terang. At Kyabram, productivity of the annual system was lower than the perennial system in the baseline scenario, but increased in future climates, assuming adequate irrigation water availability. Among sites and climate scenarios, annual per cow GHG emissions were 3.4–5.5t CO2 equivalents (CO2e), with CH4 making 0.63–0.89 of total emissions. Annual emissions per unit area ranged from 2.6 to 13.1t CO2e/ha among sites and climate scenarios, and generally reflected stocking rates. However, in the future scenarios, there were changes in N2O emissions at dryland sites due to increased direct N2O losses and lower indirect N2O through volatilisation and leaching. Annual emission intensities ranged from 7.5 to 10.9t CO2e/t milk protein plus fat among sites and climate scenarios. The lowest emissions intensity was at Elliott, which also had little change in future climates. At Terang and Ellinbank, the emission intensity was 8.8t CO2e/t MS in the baseline climate, but this increased by more than 20% in the 2070 high scenario. Results suggest that pasture based production systems can continue as the basis of the dairy industry in north-western Tasmania, but lower production and higher emission intensity at Terang and Ellinbank suggest that systems adaptations are required to meet future GHG emissions reduction goals.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Optimal plant densities of lucerne (Medicago sativa) for pasture production and soil water extraction in mixed pastures in south-western Australia

This study aimed to determine the optimal plant density of lucerne for maximum pasture productivity combined with enhanced environmental outcomes in a Mediterranean climate. Lucerne was sown at different seeding rates (1, 2, 4 or 8 kg ha−1) at two sites (Esperance and Katanning); productivity and soil water extraction was compared with an annual pasture over 4 years. Lucerne plant densities 5–6 months after seeding in 2002 ranged from 8 to 39 plants m−2 at both sites. Initial lucerne plant densities at the Esperance site were stable from 2002 until late 2004, and then began to decline, especially at the higher densities. The decline was associated with an extended dry spell. At the Katanning site, the decline was slower but constant from mid 2004 onwards with similar rates of decline for each treatment. Lucerne densities >20 plants m−2 at both sites produced more dry matter than lower plant densities (10 plants m−2) in most years. At both sites the proportion of lucerne in the total biomass increased with higher plant densities but generally at the expense of the proportion of subterranean clover. Lucerne at densities of 10 plants m−2 at Katanning had up to 30–53 mm higher soil water content to a depth of 2.6 m during summer and early autumn compared with that of >20 plants m−2. However, the differences between lucerne plant densities were smaller than the difference between lucerne and annual pasture (up to 120 mm). At Esperance the plant available soil water was limited and there were no differences between lucerne treatments. We conclude that in the 430–450 mm annual rainfall zone of south-western Australia, the higher the lucerne plant density (up to 40 plants m−2) in the first summer after establishment the more productive the pasture is in most years, the higher the proportion of lucerne in the total biomass and depending on the site the drier the soil profile. A drier soil profile can potentially reduce the spread of salinity.

Animal grazing selectivity and plant chemistry issues impact on the potential of Rhagodia preissii as an anthelmintic shrub

Rhagodia preissii had shown significant in vitro anthelmintic activity in a previous study, we examined the effect of including this shrub in the diet of sheep infected with Trichostrongylus colubriformis. Worm-infected merino wethers were grazed for 7 weeks on either R. preissii or annual pasture, and faecal egg counts (FECs) were conducted weekly. Plant material was collected weekly from eaten and uneaten plants, and analysed for levels of plant secondary metabolites (tannins, oxalates, saponins) and in vitro anthelmintic activity. While mean FECs were consistently lower in sheep grazing R. preissii compared to pasture (reductions of 20-74%), the differences were not significant. There was no relationship between grazing preference (eaten or uneaten) and in vitro anthelmintic activity of plant extracts. The levels of saponins and oxalates did not correlate with grazing preference or in vitro anthelmintic activity, while tannins were not responsible for the anthelmintic activity. While the identity of the grazing deterrent and in vitro anthelmintic compounds remain unknown, the presence of plants which were both highly preferred by the sheep and showed in vitro anthelmintic activity indicates a potential to develop the species as an anthelmintic shrub through selection of shrub populations dominated by such plants.

Improving the nutrition of Merino ewes during pregnancy increases the fleece weight and reduces the fibre diameter of their progeny's wool during their lifetime and these effects can be predicted from the ewe's liveweight profile

Nutrition of ewes during pregnancy can have permanent impacts on the production potential of their progeny. The hypothesis tested in the experiments reported in this paper was that improving the nutrition of Merino ewes during pregnancy and lactation increases the fleece weight and reduces the fibre diameter of their progeny’s wool during their lifetime. In addition, that these effects on the progeny’s wool production can be predicted from the ewe’s liveweight profile. At sites in Victoria and Western Australia in each of 2 years, a wide range in the liveweight and condition score profiles of Merino ewes was generated by varying the amount of supplements fed from joining to Day 100 of pregnancy and the amount of feed on offer grazed from Day 100 to weaning. The site in Victoria was based on perennial pastures and included both single- and twin-bearing ewes whereas the site in Western Australia was based on annual pastures and included single-bearing ewes only. The production and characteristics of wool from the progeny were measured until 51 months of age at the site in Victoria and 33 months of age at the site in Western Australia. The nutritional treatments and the resulting changes in ewe liveweight had significant impacts on the fleece weight and to a lesser extent the fibre diameter of wool produced by their progeny, but there were no consistent effects on other characteristics of progeny fleece wool. The fleece weight of the progeny was related to the liveweight change during pregnancy of their mothers (P &lt; 0.05) and the relationships were similar for the two experiments at each site. At the site in Victoria, a loss of 10 kg in ewe liveweight between joining and Day 100 of pregnancy reduced fleece weight by ~0.2 kg at each shearing until 51 months of age whereas gaining 10 kg from Day 100 of pregnancy to lambing had the opposite effect. The effect of changes in ewe liveweight during late pregnancy on the fleece weight of their progeny at each shearing was of similar magnitude at the site in Western Australia. When evident, the effect of the ewe liveweight profile on the fibre diameter of progeny wool was opposite to the effect on clean fleece weight and the effect of poor nutrition in early to mid pregnancy could be completely overcome by improving nutrition during late pregnancy. Twin-born and reared progeny produced ~0.3 kg less clean wool at each shearing (P &lt; 0.001) that was 0.3-μm broader (P &lt; 0.001) than that from single-born progeny at the site in Victoria. However, the effects of varying ewe nutrition and ewe liveweight change during pregnancy on fleece weight and fibre diameter of progeny wool were similar (P &gt; 0.05) for both single- and twin-born or reared progeny. Overall, these results supported our hypothesis and it is clear that the nutritional management of Merino ewes during pregnancy is important for optimal wool production from their progeny during their lifetime.

Relationships between soil organic matter and the soil microbial biomass (size, functional diversity, and community structure) in crop and pasture systems in a semi-arid environment

The quantity and/or quality of soil organic matter (SOM) and its fractions regulate microbial community composition and associated function. In this study an established, replicated agricultural systems trial in a semi-arid environment was used to test: (i) whether agricultural systems which have increased plant residue inputs increase the amount of labile SOM relative to total SOM, or change the quality of SOM fractions; and (ii) whether the size or quality of OM fractions is most strongly linked to the size, activity, functional diversity, and community structure of the soil microbial biomass. Soil (0–50 mm) was collected following 5 years of continuous wheat, crop rotation, crop–pasture rotation, annual pasture, or perennial pasture. Pastures were grazed by sheep. Direct drilling and non-inversion tillage techniques were compared in some cropping systems. Total carbon (C) increased with the proportion of pasture as a result of increased SOM inputs into these systems; land use also significantly affected SOM fractions and their chemical and physical nature. While the size, function, and structure of the soil microbial community were somewhat related to total soil C, they were better correlated with SOM fractions. The C : nitrogen (N) ratio of light fraction organic matter could be used to predict the amount of potentially mineralisable N in soil, while the C : N ratio of total SOM could not. Measurement of bacterial community structure (using denaturing gradient gel electrophoresis) significantly discriminated between land uses, while community-level physiological profiles revealed fewer differences. Overall, our findings support the premise that labile fractions of SOM are more strongly related to microbial community structure and function than is total SOM.

Effects of irrigation frequency on ryegrass and white clover growth. 2. Improving irrigation efficiency

Growing concerns about limited water inputs for, and deleterious environmental outputs from, irrigation of pasture make the identification of more efficient scheduling strategies imperative. A climate-driven pasture production model is used to simulate the daily soil water deficit in the topsoil and subsoil, and so pasture production under a range of irrigation strategies. Soil water content and pasture production data from a companion paper, describing a Manawatu experiment where irrigation was applied to plots at trigger deficits of 20, 40, and 60 mm, were used to evaluate model parameters. The model was then used with 30 years of meteorological data to simulate a range of irrigation strategies at Palmerston North and Winchmore. Applying 20 mm of irrigation when a 20-mm trigger deficit is reached as opposed to 60 mm of irrigation at a 60-mm deficit increased the simulated average annual pasture response to irrigation by ~80%, but this increase was at the cost of ~40% more irrigation water. A suggested alternative strategy is to apply 20 mm of irrigation whenever a 60-mm trigger deficit is reached, which in summer will be about every 5 days if no rain falls. Keeping the topsoil moist most of the time, while leaving room for rainfall in the subsoil, will increase water use efficiency (the production response per mm of irrigation) by substantially reducing the irrigation requirement and drainage excess, even though it does not maximise production.

Looking back in time: can safe pasture utilisation rates be determined using commercial paddock data in the Northern Territory?

A ‘safe’ pasture utilisation rate is defined as the proportion of annual forage growth that can be consumed by domestic livestock without adversely affecting land condition in the long term. Pasture utilisation rates are thus a cornerstone of a sustainable grazing industry because they directly determine livestock carrying capacity. Until now, it has only been possible to determine utilisation rates in the Northern Territory via expensive and time-consuming grazing trials. Reliance on this method has limited the validation of safe utilisation rates for the range of land types used for pastoral production. This study tested an alternative cost-effective method for calculating utilisation rates based on an approach used previously in Queensland. The method retrospectively calculates utilisation rates using cattle records and modelled pasture growth from commercial paddocks in good land condition. The assumption underpinning the method is that paddocks in good land condition, with a long history of grazing, must have been managed in such a way as to achieve a safe level of pasture utilisation. Utilisation rates were calculated for 10 commercial paddocks on three properties in the Barkly Tableland region of the Northern Territory from 1999 to 2009. Animal intake for each paddock was calculated from detailed cattle records held in property databases. Pasture growth was estimated using simulation models and cross-checked with field measurements. An average utilisation rate of up to 25% of annual pasture growth was found to be safe on highly uniform, grey cracking-clays supporting Mitchell grass (Astrebla F. Muell. spp.) pastures. However, this level of utilisation had negative impacts on land condition on less resilient and preferentially grazed pasture communities in paddocks with a mix of land types. The implications of the results for carrying capacity, animal productivity and seasonal risk management are explored in this paper.

Biserrula and subterranean clover can co-exist during the vegetative phase but are out-competed by capeweed

Biserrula (Biserrula pelecinus L.) is a recently domesticated annual pasture legume developed for ley farming systems that have traditionally relied upon subterranean clover (Trifolium subterraneum L.). This study examined competitive interactions between biserrula and subterranean clover and the common broad-leaf weed capeweed (Arctotheca calendula L.) during seedling establishment and vegetative growth, in order to develop guidelines for successful legume pasture management. Two glasshouse experiments were conducted to investigate the allocation of biomass to roots and shoots in biserrula, capeweed, and subterranean clover and its relationship with competitive ability in the first 100 days after sowing. In Experiment 1, capeweed had a higher relative growth rate of shoots and roots than the two legumes and developed a more extensive root system. Experiment 2 consisted of growing binary mixtures of the three species at different densities. The effect of competition on the biomass of biserrula, capeweed, and subterranean clover was best modelled by a power–exponential model. Increasing capeweed densities suppressed the biomass production of both biserrula and subterranean clover, whereas capeweed biomass increased with increasing densities of subterranean clover. This study suggests that the competitive advantage of capeweed is mainly conferred during the seedling stage. It also suggests that biserrula and subterranean clover germinating at the same time can co-exist as a mixed sward, at least up until flowering, if biserrula density is high relative to subterranean clover.

New strains of rhizobia that nodulate regenerating messina (Melilotus siculus) plants in saline soils

Messina [Melilotus siculus (Turra) Vitman ex B.D.Jacks (syn. M. messanensis (L.) Mill.)] is the most promising annual pasture legume for saline waterlogged soils in southern Australia. Messina forms a symbiosis with the commercial Sinorhizobium medicae strain, WSM 1115, used for many annual medic (Medicago) species. However, WSM 1115 does not persist over the summer months in saline soils and fails to adequately nodulate regenerating messina plants, restricting its commercial development as a new species for agriculture. To overcome this symbiotic constraint, two field experiments (swards and rows) and a glasshouse symbiotic effectiveness experiment were undertaken to identify strains of S. medicae able to persist in saline soils and adequately nodulate regenerating messina plants. In the sward experiment, no rhizobia were detected in WSM 1115 plots in the first autumn following seed set, whereas 3519 rhizobia per g of soil were measured for strain SRDI 554. Compared with WSM 1115, SRDI 554 increased regenerating messina nodulation from 32 to 100%, the number of nodules per plant from 1.3 to 32.4 and shoot dry weights from 23.6 to 80.2 mg/plant. The row field experiment found SRDI 554 had greater saprophytic competence than WSM 1115 and increased overall mean plant nodulation from 11 to 74%. The symbiotic effectiveness experiment found plant shoot weight of the majority of S. medicae strains under non-saline conditions was similar to WSM 1115. These experiments have identified new strains of rhizobia that overcome the symbiotic constraint in regenerating messina plants in saline soils. Further evaluation, particularly in acidic saline, waterlogged soils, is required to confirm adaptation of the most promising strains to soils within the full range of messina target environments.

Soil carbon dynamics under different cropping and pasture management in temperate Australia: Results of three long-term experiments

In addition to its important influence on soil quality and therefore crop productivity, soil organic carbon (SOC) has also been identified as a possible C sink for sequestering atmospheric carbon dioxide. Limited data are available on the impact of management practices on the rate of SOC change in agricultural soils in Australia. In this paper, results of three long-term trials (13–25 years) located near Wagga Wagga in temperate Australia were used to assess C dynamics under different tillage and stubble management practices, and under cropping intensities in pasture/crop rotations. Experimental results confirm the importance of management practices and pasture in determining first the steady-state SOC concentrations that are characteristic of given rotations and crop management systems, and second the rates of change of SOC concentrations as they approach steady-state concentrations in agricultural soils of this agro-ecological zone. A long-term crop/pasture experiment at a site with initial high SOC showed that the rate of SOC change in different treatments ranged from –278 to +257 kg C/ha.year over 0–0.3 m soil depth. Under continuous cropping, even under conservation agriculture practices of no-tillage, stubble retention, and crop rotation, the high initial SOC stock (0–0.3 m) present after a long-term pasture phase was, at best, maintained but tended to decrease with increased tillage or stubble burning practices. The effect of tillage was greater than that of stubble management. Increases in SOC were observed only in rotations incorporating a pasture phase. Our results suggest that improved soil nutrient and grazing management of permanent pasture can lead to an increase of 500–700 kg C/ha.year where the initial SOC concentrations are well below steady-state concentrations that could be expected after long periods of improved management. No difference was found between perennial pasture and annual pasture to the depth measured (0–0.3 m). Our results suggest that pasture holds the key to maintaining, and even increasing, SOC under crop/pasture in this environment.

Steps toward sustainable ranching: An emergy evaluation of conventional and holistic management in Chiapas, Mexico

Conventional ranching in Chiapas, Mexico typically includes annual pasture burns and agrochemical use that decrease the biodiversity and forest cover of ranch lands. Members of a holistic ranching “club” in the Frailesca region of Chiapas, Mexico have moved away from this conventional management by eliminating burns and agrochemicals from their systems after decades of use because they believed that the land and their production process were growing unhealthy; they were further motivated by extension courses on holistic ranching. They have also implemented sophisticated systems of rotational grazing and diversified the use of trees. For this study all seven holistic ranchers and 18 neighboring conventional ranchers were interviewed about their cattle ranches and production strategies. An emergy analysis was conducted to compare the resource use, productivity and sustainability of the conventional and holistic ranches. Holistic ranches were found to have double the emergy sustainability index (ESI) values of conventional ranches, and the emergy yield ratio was 25% higher in holistic systems. Government assistance programs were found to have a negative impact on the ESI and were variably administered among holistic ranchers during the year of emergy evaluation. Overall improved emergy sustainability did not decrease milk nor cattle productivity. Transformities and specific emergies, the emergy of one type required to make a unit of energy (transformity) or mass (specific emergy) of another type, did not differ between conventional and holistic systems. Transformities for milk production ranged between 3.4E5 and 1.2E7 solar emjoules/joule (sej/J). Specific emergy for cattle production ranged from 3.5E10 to 1.5E11 sej/g. To improve the ESI assistance programs could be re-targeted toward incentive programs for increased forest cover in ranching systems and startup costs for holistic ranching. The results from this study show that productivity can be maintained as the sustainability of rural dairy ranches is increased. These results also show that local knowledge and understanding of the surrounding ecosystem can drive positive environmental change in production systems.

Short-term grazing of lucerne and chicory increases ovulation rate in synchronised Merino ewes

This study evaluated the ability of short-term grazing of live = green pasture to increase ovulation rate during late summer when annual pasture is generally dead and of low quality. Ovulation rates, measured by the number of corpora lutea, were compared between 4 nutritional treatments: senesced phalaris ( Phalaris aquatica), phalaris plus 500 g lupin grain per day, lucerne ( Medicago sativa) or chicory ( Chicorum intybus) pastures. The study used 100 Merino ewes per treatment, divided between 2 replicates. The experiment was repeated in 3 years; February 2006, and January 2007 and 2008. Oestrus was synchronised and the ewes grazed the pastures for 9 days prior to ovulation at times corresponding to days 8–17 of the cycle in 2006, and days 6–14 in 2007 and 2008. The proportion of ewes producing multiple ovulations was higher ( P < 0.05) in the lucerne and chicory (0.36, 0.38) than the phalaris (0.27), and intermediate in the lupin (0.33) treatment. Regression analysis showed that the proportion of ewes with multiple ovulations increased with the quantity of live herbage ( P < 0.04). Responses were achieved even at low levels of live herbage with 90% of the maximum proportion of multiples occurring at 350 kg DM/ha. It is concluded that providing short-term grazing of live chicory or lucerne to ewes can increase ovulation rates relative to ewes grazing senesced phalaris and to levels similar to those achieved by lupin grain supplementation.