White clover (Trifolium repens) is a valuable forage and soil fertility resource whose persistence and contribution to production and profitability can be constrained by genetic, farm management, and environmental factors. Here we outline the growth stages of the plant, and factors affecting persistence at the plant and the population level in pasture. Breeding strategies that bring together new germplasm sources within white clover have improved persistence on farm. New experimental lines, including some accessing genetics from related Trifolium species, show advances in forage productivity and persistence in multi-site, mixed sward, trial systems under dairy, sheep and cattle grazing. New germplasm sources and the use of new tools for characterising and selecting superior plant material will enable increased genetic gain for traits including persistence and forage production in white clover and related forage legumes. Keywords: Lolium perenne, pasture, persistence, stolon density, Trifolium repens, white clover
A ryegrass breeding programme to improve the seasonal growth and plant persistence of perennial and hybrid ryegrasses in the Waikato began at AgResearch Ruakura, Hamilton in 2001. One approach was to characterise the genetic diversity of the naturalised populations within 26 dairy farms from different districts around the Waikato and Bay of Plenty (BOP) regions. Plants from 26 individual breeding lines were evaluated as single spaced plants over a 3-year period in comparison with three commercialised ryegrass cultivars. Principal Component Analysis was used to order the plant populations in accordance with the observed plant variables of seasonal growth pattern, tillering ability, leaf size and extension, and the incidence of crown rust. A hierarchical cluster analysis of the wild populations revealed two distinct plant groups. A mix of large leaf Italian Lolium multiflorum and hybrid plants were typical from the warmer drier areas of the BOP. The Italian ryegrass was prone to severe crown rust infection whereas the hybrids were more resistant. Shorter, narrow leaved and densely tillered plants with a high rust infection dominated the Waikato populations. Ecotypes that maintained high plant tiller density throughout the seasons had the best persistence. Plants that displayed an improvement in seasonal yield and tillering over the commercial cultivars were considered an important genetic source to develop new persistent cultivars for the Waikato and BOP regions. Keywords crown rust, drought, ecotypes, Lolium spp., plant breeding
A methodology is developed to analyse the contribution to sward persistence of the processes tiller birth and tiller death, and variation in their rate over an annual cycle. The methodology is tested using previously published data for timothy grass (Phleum pratense). The analysis shows that high death rates of timothy tillers in summer present a problem for persistence in that tiller appearance rates required to maintain the tiller population in these conditions require tiller bud site usage statistics that are biologically unlikely in field swards. While it is not suggested that ryegrass has a naturally high tiller death rate in summer as demonstrated here for timothy, where abiotic stresses reduce ryegrass tiller survival, the same principles are likely to apply. Keywords: Leslie matrix, Phleum pratense, population stability, tiller birth rate, tiller survival rate, timothy grass
An outbreak of the pasture insect pest black beetle began in the Waikato and Bay of Plenty in 2007/8 and has persisted. The extent and severity of damage caused by black beetle during the current outbreak has focused farmer and researcher attention on methods to maintain persistent pasture now and in future outbreaks. This paper reviews previous research in combination with data from the current outbreak and relates these to current pasture management practice. The possibility of being able to predict the distribution, occurrence and duration of black beetle outbreaks is explored while actual and potential means of controlling black beetle are outlined. We conclude that there are methods available to successfully renew pastures in the presence of black beetle but that outbreak situations increase risks and may limit subsequent pasture persistence. There are fewer readily available options to maintain an existing pasture and more research is urgently needed to provide these options. Keywords: Heteronychus arator, paspalum, pasture, pasture renewal, pest resistance, pest tolerance, ryegrass
Recent discussion about pasture persistence concentrates on pastures based on perennial ryegrass, the most commonly used grass species. This paper raises the question as to whether some of the causes of poor pasture persistence are due to perennial ryegrass being used in environments to which it is not suited. The adaptation to environmental stresses, particularly water, temperature and nutrient deficiencies, in different regions of New Zealand of tall fescue, cocksfoot, phalaris, and lucerne are discussed, and how this impacts on persistence advantages over perennial ryegrass. Keywords: persistence, pasture, Dactylis glomerata, Festuca arundinacea, Lolium perenne, Medicago sativa, Phalaris aquatica
From 1990 to 2010 there have been major changes in New Zealand pastoral agriculture. The intensification of the dairy industry has led to higher stocking rates, lower grazing residual DM, higher N fertiliser use and increased supplementation. However, there is little evidence that these changes are responsible for the decreased persistence of ryegrass-based pastures, rather the interactions between low summer rainfall, low water-holding capacity soils, endophyte status and cultivar ‘type’ have caused significant pasture damage. These factors, together with plant nutrient status (especially N) and plant population survival mechanisms (tiller dormancy, birth and death rates, seed production and establishment) are hypothesised to be the primary drivers of ryegrass persistence. A secondary subset of pests, diseases, weeds and high grazing intensity (pugging and pasture ‘pulling’) are considered to interact with the primary drivers to compromise ryegrass tiller survival. Attention to plant species and cultivar selection, tiller replacement mechanisms and ryegrass cultivar development are required to improve ryegrass persistence. Keywords: climate, dairy, N fertiliser, perennial ryegrass, white clover
This manuscript reviews fundamental pasture management principles relevant to pasture persistence. We first note some points of context, within which the debate on pasture persistence is occurring: the release of new pasture cultivars, the debate about climate change, and the effects of newly introduced weeds and pests. We then examine trends in farm practice. The critical management period (of most concern to farmers) has shifted from winter/autumn to summer. It is essential that farmers have and use sets of decision rules to govern when and how hard to graze, when to supplement and when to remove cows from pasture to allow pastures to be grazed appropriately to aid pasture persistence. Adaptations available to improve pasture persistence include: the use of nitrogen fertiliser to increase feed supply going into the summer, the use of crops or other feed supplements, stocking rate and on-off grazing to ensure the pastures are appropriately grazed in the summer. New pastures must be treated with care in their first year of life to ensure survival. The response of farmers to these variables to aid persistence of pastures is discussed. Keywords: climate, insect pests, pasture growth model, pasture renewal, weeds
This trial provided information about effects of defoliation frequency, defoliation intensity and winter management (grazing or rest) on the productivity, morphology and plant population of a 3-year-old plantain (Plantago lanceolata) stand. Plant population density declined drastically over time independently of grazing management, with the greatest decrease in summer. Winter grazing had a critical effect on the productivity and population remaining 6 months later. Frequent grazing during summer increased plantain contribution. Grazing intensity reduced crown weight and diameter of individual plants. Further studies are required to determine the interactions of defoliation management with pastures of different age including the natural reseeding as a mechanism to maintain plant recruitment. Keywords: defoliation, grazing, morphology, population
Soils are the substrate at the base of any grazing or cropping system providing plants with nutrients, water and physical support, a habitat for beneficial organisms and a physical base on which animals stand. A change or a loss of any one of these soil services has the potential to impact on plant growth and persistence. The findings of two ongoing field-based studies are presented and discussed as they relate to the current debate on pasture persistence. One study is investigating the influence of the physical condition of the soil on a ryegrassbased pasture response to added phosphorus (P). The second study is investigating the P requirements of high producing perennial ryegrass and tall fescuebased pastures, where the constraints to pasture growth and associated P uptake imposed by low nitrogen availability and low soil moisture over summer-autumn have been removed. The critical Olsen P value for maximum pasture production appears to increase as the constraints to pasture growth are removed. This challenges the continued use of a single relative yield Olsen P function and one critical Olsen P value for near maximum yield regardless of the absolute pasture yield. Loss of soil pore function also appears to increase the critical Olsen P value necessary for optimum pasture growth. Additional P can compensate for a lack of pore function to a degree, but there appears to be an upper limit to this effect. Given that the physical condition of many of our pasture soils in intensive lowland situations is below optimum, nutrient stress may be more of a factor in poor pasture-persistence, than previously thought. Inclusion of a measure of soil physical condition would appear to warrant further study in defining the conditions for optimum plant growth and persistence. Keywords: fertiliser nitrogen, Festuca arundinacea, Lolium perenne, Olsen P, pasture persistence, soil pore function, soil services
Fungal endophytes reduce populations and damage by several different insect pests which alone or in combination with each other can reduce ryegrass persistence. AR1, AR37, the Standard endophytes and two endophytes in tetraploid ryegrasses, NEA2 in cv. Bealey and Endo5 in cvs. Quartet II and Banquet II, are available to the New Zealand farmer. Their effects on insects depend on the spectrum and concentration of alkaloids they produce. Argentine stem weevil is controlled by all endophytes except perhaps Bealey NEA2; black beetle is controlled by all endophytes except AR1; pasture mealybug are controlled by AR1, AR37 and Standard and likely to also be controlled by Endo5 and NEA2; porina and root aphid are controlled by AR37. Increased persistence of ryegrass infected with endophyte is reflected in increases in endophyte infection rates in pasture, higher yields and tiller densities and reduced weed invasion, particularly where climatic stress is also present. AR37, with the protection it provides against a range of insect pests, is the most effective endophyte for improving persistence. Keywords: alkaloids, Argentine stem weevil, black beetle, insect damage, Neotyphodium
How do we know which pastures to renew and do we increase profitability when we renew them? An inventory of pasture production of the Telford dairy farm was developed using paddock grazing records to estimate potential pasture production and variability from different soil types. Using the difference between low and high producing pastures as the potential for improvement, the change in pasture production with renewal was calculated and valued using several methods, from the simple conversion of extra dry matter into milk solids production through to whole farm systems optimisation using Farmax Dairy Pro. The cost of pasture renewal was highest when valued by the Pasture Renewal Charitable Trust model when the cost of lost grazing was estimated. The return for pasture renewal was lowest from Farmax Dairy Pro modelling when whole farm-integration was considered. At the average value of milk for the last 5 years, the payback period was between 2.5 and 3.1 years, depending on the model used. Keywords: analysis, modelling, pasture production records, pasture renewal, soil types.
Welcome to the Pasture Persistence Symposium. This Symposium is being held under the auspices of the New Zealand Grassland Association to help understand and improve the persistence of particularly ryegrass based pastures.
Core samples were taken from 60-year-old pastures on a long-term fertiliser trial at the Winchmore research station, in Canterbury, New Zealand. Plots had been treated with 0, 188 or 376 kg/ha of superphosphate annually, grazed by sheep, and pasture yields were recorded. Ryegrass persisted in all treatments, but was only dominant in the superphosphate treatments, unsown grasses dominated in the no superphosphate treatments. White clover was more common with superphosphate, and both cocksfoot and timothy required adequate superphosphate in order to persist. Over 60 years of measurements, yields were 9-15 t DM/ ha with superphosphate, and did not reduce over time. Given adequate fertiliser, a ryegrass-based irrigated pasture can continue to produce high yields 60 years following sowing. Keywords: ryegrass, cocksfoot, t
A measure of pasture persistence is stability of yield and proportion of desirable species over a long period. Long-term data on animal production and pasture yield and composition of old permanent pasture in the Manawatu were examined for trends indicative of persistence. The data were collected from two sets of replicated 1.6-ha farmlets intensively grazed by dairybeef bulls stocked at 7.4 yearlings wintered/ha for 16 of 18 years from 1969-1986, and 11 years from 1978 and 1988, respectively. Annual total LWG, total yield of DM and the yields of ryegrass, white clover and other species showed year-to-year variation. There was no long-term decline in production indicating that for this environment and management system ryegrass and white clover were inherently persistent under intensive grazing at high stocking rates. These results are discussed in the context of anecdotal reports of poor persistence of modern cultivars, with particular emphasis on the effects that high stocking rates, intensive utilisation and defoliation management may have on persistence. Keywords: cattle, grazing, pasture, persistence, ryegrass, white clover
Pasture persistence is highly rated by sheep and beef farmers as an important factor determining wholefarm performance. Managing pastures to ensure the persistence of newly sown pasture species must be considered as a part of the decision making process of the whole farm. The farmer aims to optimise the outcomes of resource use over time, rather than maximise any single resource, and therefore grazing decisions must be considered in this context. Pasture renewal is a major event-driven disruption that replaces current pasture species with competitive species, creating a grass-legume complex that has a tendency to develop towards a community of plants that tolerate the local environmental stress. Pasture persistence can be improved through managing the impacts of and interactions between environmental stressors on the pasture. Interactions between pasture management options, such as grazing and fertiliser, and the major environmental stressors of soil moisture, temperature, soil fertility, grazing and pests are discussed. Keywords: ecology, environmental stressors, farm systems, grazing management, pasture persistence.
Farmers have indicated that perennial pastures sown in the Lake Taupo catchment revert to low quality species within 8 to 10 years. These may be renewed with perennial pasture species following an autumn then spring cropping regime, or resown pasture-topasture by direct-drilling into glyphosate-sprayed turf or following full cultivation. Vegetation which is desiccated and/or ploughed-under before sowing will decay and release mineral nitrogen (N). The mineral N from these sources is available for newly sown plants but can also be leached. In a large, replicated, rotationally cattle-grazed trial near Lake Taupo, new pasture was established with the high sugar ryegrass (HSG) Aberdart in one treatment only by direct-drilling, following glyphosate application in late summer. Existing pasture remained in Control plots. Renovated pasture leached 63 kg nitrate-N ha-1 in the 8 months following establishment compared 8 kg nitrate-N ha-1 in Control (P<0.05). There were no differences in the amount of leached N amongst treatments in the second year (P=0.1). Nitrogen leaching losses resulting from pasture renovation and forage cropping practices are discussed in relation to the impacts these have on future pasture management and renewal options and on the potential value of new germplasm in the Lake Taupo catchment, whose management is constrained by a N cap. Keywords: nitrogen leaching, pasture establishment, Taupo
A review of recently published science demonstrates that relatively simple non–perennial ryegrass mixtures have performed well in environments as diverse as under deer grazing in Dunedin and the Manawatu, under sheep grazing in dryland mid-Canterbury, and under both irrigated and dryland dairy cow grazing in the Waikato and Northland. Animal productivity has been lifted by up to 30% in milk solids and 50% in deer liveweight gain in non-perennial ryegrass mixtures compared to perennial ryegrass-based pastures. In some cases, the ryegrass pasture has produced similar or more dry matter, yet animal performance has been greater on the non-perennial ryegrass pastures. In other cases, dry matter productivity from complex nonryegrass mixtures has been around 30% higher than from perennial ryegrass pastures. Interviews with farmers from South Canterbury to Northland have all reported positive experiences with non-ryegrass pastures and most have said they will not be planting perennial ryegrass-based pastures again.
This essay contains personal observations and interpretations by the author on the persistence of pastures in the northern North Island. Key pasture stress factors are identified as the increase of farming intensity over the past two decades, the impact of pasture renewal techniques and the role of pasture species on insect pest (particularly black beetle and clover root weevil) interactions. Keywords: insect pests, soil fertility, pasture renewal, cultivars, endophyte
Information is presented on farmer perceptions and concerns regarding key factors leading to poor persistence of sown pasture species. Forty-seven farmers from four regions viz. Northland (beef, sheep), Waikato (dairy), Taranaki (dairy) and North Canterbury (beef, sheep, deer) were asked for their opinions on the ‘keys’ to persistence and ‘killers’ of sown species; i.e., factors leading to a decline in sown species. In all regions, grazing management was perceived to be the most important key to persistence and insect pests the top killer of sown species. Better industry dissemination of existing information and further research on forage herbs and insect pest issues are future requirements. In each region, presence of sown species was also assessed in 30 paddocks belonging to the surveyed farmers. There was a significant decline in pasture chicory presence, but no decline in that of cocksfoot or plantain. Ryegrass, white clover and tall fescue were present in nearly all paddocks in which they were sown. Chicory may be best used as a crop, while plantain shows greater potential for persistence as part of a pasture mix. Keywords: chicory; farmer survey; information gaps; plantain; research needs
The farm system model, Farmax Dairy Pro, was used to evaluate the impact of new pastures on dairy farm profitability, assuming a range of pasture yields and qualities, and different levels of persistence in the new pastures, which were established on 10% of the farm annually. Scenarios were tested for Waikato, Taranaki, Canterbury and Southland dairy farm systems. Assuming a $6.50/kg MS milk payment and a response to pasture renewal of 10% in dry matter yield and a 0.6 MJ ME/kg DM increase in quality, increasing persistence from 4 years up to 8 years was modelled to increase dairy farm profitability by $271/ha to $478/ha. Management practices, including selections of cultivars and endophytes, that improve pasture persistence are likely to increase dairy farm profitability. Keywords: dairy farms, modelling, pasture renewal, persistence
Pasture persistence and performance, and associated issues such as black beetle, are of central concern to dairy farmers. The Pasture Renewal Survey 2010 aimed to better understand farmers’ confidence in their ability to make informed decisions on their pasture renewal practices, their satisfaction with the success of this decision-making and the performance of their renewed pastures over time. In addition, the survey investigated their attitudes to information sources and what barriers they saw to improving pasture performance on farm. A postal and online survey elicited responses from 776 dairy farmers in the Waikato and Bay of Plenty regions. The four main findings of the work were: 1. Farmers are more confident of their ability to make appropriate on-farm management decisions for renewed pasture than they are of their ability to choose appropriate cultivars and endophyte. 2. Farmers, while generally satisfied with their own success in renewing pasture, reported decreasing levels of satisfaction with renewed pastures over the 3 successive years following renewal. 3. Farmers do not rate information sources very highly in terms of their usefulness in relation to pasture renewal. 4. Weather-related issues and pest-related issues (particularly black beetle) were the most commonly identified barriers to improving pasture performance. Keywords: farmer confidence, farmer satisfaction, information sources, pasture renewal.
Recent experiments have demonstrated that lucerne (Medicago sativa) varieties selected for grazing tolerance will persist far better when grazed for extended periods than varieties not selected for grazing tolerance. A field experiment, with lucerne varieties representing a range of winter activity ratings, was conducted at Ballarat. After 2.5 years of rotational grazing the experiment was continuously grazed for 173 days from late spring to early autumn at a stocking rate equivalent to 50 sheep/ha. This intensity is not considered much higher than some farmers would adopt during a drought. Ground cover of some varieties had significantly declined by the end of the grazing period but further decline occurred throughout the following winter months while livestock were excluded. The grazing tolerant lines persisted better than most standards, even those within the same dormancy category, with some standards almost completely dead while the grazing tolerant lines were over 60% alive. Keywords: grazing tolerance, lucerne (Medicago sativa), persistence
Recent experiments have demonstrated that lucerne (Medicago sativa) varieties selected for grazing tolerance will persist far better when grazed for extended periods than varieties not selected for grazing tolerance. A field experiment, with lucerne varieties representing a range of winter activity ratings, was conducted at Ballarat. After 2.5 years of rotational grazing the experiment was continuously grazed for 173 days from late spring to early autumn at a stocking rate equivalent to 50 sheep/ha. This intensity is not considered much higher than some farmers would adopt during a drought. Ground cover of some varieties had significantly declined by the end of the grazing period but further decline occurred throughout the following winter months while livestock were excluded. The grazing tolerant lines persisted better than most standards, even those within the same dormancy category, with some standards almost completely dead while the grazing tolerant lines were over 60% alive. Keywords: grazing tolerance, lucerne (Medicago sativa), persistence
Relationships between climatic factors and persistence of grazed perennial ryegrass and white clover pastures in New Zealand are reviewed from an ecophysiological perspective. ‘Persistence’ is defined in terms of physical survival of plants of sown cultivars: the effects of climate on plant populations are considered. Substantial information is available on the population dynamics of perennial ryegrass and white clover in different climatic environments, particularly on the influence of drought on populations. Substantial, direct negative effects of drought on the density of perennial ryegrass tillers and white clover stolons have been recorded, though populations have generally recovered after release from drought conditions. Otherwise, the effects of climaterelated resource limitations on population size are more likely to be interactive, working in concert with other factors such as management, soil fertility and insect pest challenges to limit the capacity of homeostatic responses to restore the optimal (for long term survival) balance between above- and below-ground resources. The relative extent to which more recent cultivars of perennial ryegrass are able to tolerate multiple, simultaneous resource limitations compared to older cultivars (with different phenotype) is considered, but there is little direct evidence on this matter. Issues that should be considered in future pasture persistence research are identified and discussed. One of these concerns is the persistence of trait expression in cultivars bred for specific traits. More research on this topic is warranted, since molecular plant breeding techniques are strongly based on trait manipulation, and genotype x environment interactions can be expected in the spatially and temporally variable environment of grazed pastures. Keywords: drought, ecology, plant breeding, ryegrass, white clover
The effects of defoliation on plant morphology and the structure of perennial ryegrass and white clover populations are reviewed with reference to the persistence of yield in sown pastures. Maintenance of high densities of perennial ryegrass tillers and white clover stolons is fundamental to persistence. Tiller and stolon population densities are subject to within- and between-year variation, and are strongly influenced by defoliation management through processes such as competition for light, and size-density trade-offs mediated by self-thinning processes. Spring is a time when high tiller/stolon appearance and death rates occur simultaneously. Spring is also the time when clover populations undergo rapid structural change as large clover plants fragment to release small, unbranched plants with limited ability to compete for light with grasses. The central role of reproductive stem development in perennial ryegrass for summer survival of tillers and autumn re-establishment of tiller populations also highlights the importance of defoliation management during the spring for population persistence. Examples of the application of tactical defoliation management in spring, and at other times of the year, to manipulate stolon and tiller densities are presented. In some instances, such tactics may improve animal production potential, as well as the persistence of new cultivars. It is notable that the New Zealand literature on this topic is mostly more than 15 years old. Recent changes in farming systems and plant genotypes (e.g. tetraploidy in perennial ryegrass, late flowering perennial ryegrass) may require a reanalysis of established principles and practices related to defoliation x plant interactions in grazed pastures to ensure best possible pasture yield persistence and profitability of grazing systems. Keywords: grazing management, perennial ryegrass, persistence, population dynamics, white clover
A review of the literature shows that soil compaction by stock treading has been an issue for New Zealand farmers for over half a century. Soil compaction restricts root penetration resulting in poor anchorage and susceptibility of plants to uprooting during grazing. In addition, access to moisture and soil nutrients is reduced which decreases the fitness of the sward under stress conditions. Mechanical treatment of compacted soil improves soil physical properties but beneficial effects on pasture growth have been less readily demonstrated. Options to reduce the impact of soil compaction on pasture persistency include better soil management to reduce the incidence and severity of compaction and, in the longer term, new grasses with root and shoot traits that mitigate the effects of compaction. Keywords: roots, ryegrass, soil compaction, soil moisture, soil nutrients, trampling
The suggestion that modern pasture cultivars persist less well than their predecessors is not supported by facts. However in some regions there is a crisis in farmer experience of persistence of ryegrass pastures, and ryegrass breeding can contribute to a resolution. This paper considers the turnover of tillers in a pasture, the population structure of a grass sward and the involvement of endophyte and companion clover. Knowledge gaps in key processes of pasture persistence are discussed. The plant breeding process involves access to relevant genetic variation, its assessment, and creation of improved populations and eventually cultivars based on selected superior plants. All these scientific processes use ever-evolving techniques. Breeding objectives evolve with industry needs and the changing environment. The methods employed in the breeding phases, the breeding objectives and the final evaluation of cultivars require ongoing revision. Plant breeding will make a growing contribution to modern farming if its developing capabilities are interfaced with other research disciplines providing critical information on key pasture processes. Keywords: Lolium perenne, endophyte, persistence, tillering
Several invasive European slug species are thriving in New Zealand and have become important pests of many crops. In pasture, they are particularly damaging to white clover during renovation and the problem may be exacerbated by direct drilling. Slug feeding causes both lethal and sublethal damage that reduces clover establishment and thus pasture quality. Much less is known about slug damage to established pastures and the degree to which slugs limit pasture persistence. Established pastures frequently support large slug populations that feed on clover and the application of molluscicides can reduce slug numbers and increase the proportion and yields of clover. Future research on these pests should concentrate on determining damage thresholds, breeding resistant clover varieties and developing agronomic practices that favour natural enemies. In the long term, there is much potential for developing microbiological pesticides that target slugs. Keywords: molluscs, slugs, clover
Methods of achieving successful pasture establishment have been broadened over the last 50 years by the introduction of no-tillage technologies, providing a viable alternative to cultivation. Parallel developments in drill technologies for seed and fertiliser placement, and methods to control competition from the existing pasture have ensured the success of no-tillage methods. This review focuses on the effects of the establishment method on seedling growth over the establishment period, defined for the purposes of this paper as the year after sowing. Undersowing existing pasture is the establishment method least likely to provide a suitable environment for seedling growth and development. New pastures must receive different management to existing pastures for at least 1 year after sowing to increase their chances of becoming persistent and productive. Long-term monitoring (5-10 years) of new pastures has received little research attention, making assessments of effects of different establishment methods on persistence difficult. Factors likely to affect seedling establishment and plant survival are discussed. Keywords: competition control, cultivation, directdrilling, first year management, Lolium perenne, ryegrass, seedling survival, Trifolium repens, white clover
Three datasets spanning 31 years (1979-2010) of net herbage accumulation (HA) for Waikato dairy pastures were studied to determine between-year variability in summer HA. In addition, a dairy farm at the same location was modelled with the DairyNZ Whole Farm Model, using climate data for 15 years to predict HA, and milksolids production. Measured extremes for HA over 5 months (1st December to 30th April inclusive) were from 4.7 to 9.1 t DM/ha, with a mean of 7.0 t DM/ ha ±1.2 t DM/ha SD. Rainfall during these months had a positive impact on HA, with an extra 849 kg DM/ ha (r2=0.43, p<0.001) grown in December to April for every additional 100 mm of rainfall. December- April rainfall during 1979-1993 was 17% more than December to April 2004-2010. For the modelled farm stocked at 3.1 cows/ ha, December to April HA was predicted to average 6.6 ±1.3 t DM/ha, ranging from 4.7 to 8.7 t DM/ha. In 2 years out of 3, HA was predicted to be below feed demand from December to April. Clearly, managing pastures to recommended post-grazing residuals and pre-grazing leaf stage in summer can be problematic when the variability in HA is large and there is limited capacity to reduce stocking rate and hence feed demand. Repeatedly exceeding pre-grazing herbage mass targets in good summer HA years and post-grazing residual targets in poor summer HA years are both scenarios consistent with the loss of perennial ryegrass plants from dairy pastures and this study examines the historical frequency and size of such events. Keywords: annual variation, grazing management, Lolium perenne, summer herbage accumulation, stocking rate
New Zealand pastures are host to a range of native and exotic invertebrates. Many of these are pests that feed on the sown plant species, often causing plant death and deterioration in the productivity and persistence of the sward. While most research has focused on pest biology and control, studies of plant productivity show dramatic acute (short-medium term) and chronic (longterm) effects. For example, grass grub has been reported to cause 50% losses to ryegrass swards and Argentine stem weevil can cause a 20% loss of productivity, but the long term effects through loss of the sown species and changes in composition can be even more severe. Insect damage can be exacerbated by other biotic (e.g. weed invasion, grazing animals, plant pathogens) or abiotic factors (e.g. climate, soil fertility) to further reduce plant persistence. Some biotic and abiotic factors may interact with insect pests to have positive effects on pasture persistence, e.g. biocontrol agents that reduce pest density or addition of fertiliser to enable plants to recover from insect damage. For many pasture pests, knowledge of their ecology is based on research from over 20 years ago that, while still valid, needs to be updated to account for modern intensive pasture management practices, such as intensive grazing with a lack of reseeding, and new cultivars. To improve pasture persistence, integrated research programmes are needed that examine the relative importance of all factors contributing to plant survival and develop strategies to mitigate their effects. Keywords: Argentine stem weevil, black beetle, clover root weevil, drought, grass grub, grazing pressure, manuka beetle, nematodes, pasture persistence, pasture quality, pasture yield, porina, soil fertility, striped chafer.
Maize is a drought tolerant crop that produces high dry matter yields. Growing maize silage as part of a pasture renewal programme can help improve pasture persistence by reducing the level of weeds, insect pests and carryover ryegrass seed. Feeding maize silage to dairy cows results in pasture substitution. This decreases grazing pressure and can be used to manipulate farm pasture cover levels reducing overgrazing. The combination of maize silage and a well-designed stand-off pad with feeding bins allows farmers to keep cows off wet pastures reducing pugging damage and subsequent losses in pasture production without compromising milk production or animal welfare. Maize hybrid selection is critical to ensure timely regrassing. Crop simulation models such as CERES-maize may be useful to determine the best maize hybrid maturity x planting date combinations required to maximise silage yield and meet desired silage harvest and regrassing dates. Best-practice maize silage management including seed bed preparation, weed control and insecticide-treated maize seed will help farmers achieve high yields of silage and assist in the subsequent establishment of high yielding and persistent pastures. Keywords: pasture persistence, maize silage, feed pad
In an ideal pasture, sown species would persist indefinitely and there would be no weeds. ‘Poor persistence’ occurs when the desirable species are replaced by weedy, undesirable species. Unfortunately, poor persistence of sown pasture plants is the reality that most farmers experience. In this paper we review the literature on three key factors leading to poor persistence and weed ingress: 1) inter-specific competition; 2) sward disturbance; and 3) propagule pressure. We reveal that grazing and other management decisions, pasture insect pests, nutrients, climate and the composition of the sown species mix have a critical influence on these factors, and hence over the replacement of sown pasture plants by weeds. The key practical message from this review is that farm practices that improve the vigour of sown species, reduce pasture gaps and minimise weed propagule pressure will improve the persistence of sown species and minimise weed ingress. An outstanding deficiency is our lack of knowledge of the economic impacts, and hence weed status, of most of the ca 187 volunteer plant species that may invade and replace sown plants in New Zealand’s pastures.
White clover is relied upon as a cornerstone of the international competiveness of New Zealand’s pastoral sector, despite its vegetative persistence and yield being constrained by pests and diseases. The species’ vulnerability has been highlighted by the clover root weevil (Sitona lepidus) incursion, and the impact of increased residual pest and pathogen loadings under minimum tillage techniques. Plant breeding with a focus on plant health has made improvements in white clover performance, and there is scope to develop varieties that ensure a more resilient legume component in pastures. An exemplar outcome from this approach is improved vegetative persistence and dry matter yield under nematode and clover root weevil pressure, as shown in field trials of elite breeding material. An enhanced, unified plant breeding and plant health approach can increase the performance and vegetative persistence of white clover. Trait selections to increase resilience and dry matter yield include optimum root architecture; single and multi-gene resistance or tolerance mechanisms; multi-pest defence compounds; and symbiont:clover combinations enabling induced pest and disease resistance. Cost effective and timely plant health assays for plant breeding are essential. Improved breeding strategies will create value on-farm via perennial forage legumes that perform better under pressure from pests. Keywords: white clover, plant breeding, plant genetics, nematode, pest resistance, pest tolerance
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