K.N. Tozer

Simple versus diverse pastures: opportunities and challenges in dairy systems

For Australian and New Zealand dairy farms, the primary source of home-grown feed comes from grazed perennial pastures. The high utilisation of perennial pasture is a key factor in the low cost of production of Australian and New Zealand dairy systems and, hence, in their ability to maintain international competiveness. The major pasture species used are perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), normally grown in a simple binary mixture. As pasture production has been further driven by increasing use of nitrogen fertiliser and irrigation, farms are getting closer to their economic optimum level of pasture utilisation. Increasing inputs and intensification have also increased scrutiny on the environmental footprint of dairy production. Increasing the diversity of pasture species within dairy swards presents opportunities to further increase pasture utilisation through additional forage production, extending the growing season, improving forage nutritive characteristics and, ultimately, increasing milk production per cow and/or per hectare. Diverse pastures also present an opportunity to mitigate some of the environmental consequences associated with intensive pasture-based dairy systems. A consistent finding of experiments investigating diverse pastures is that their benefits are due to the attributes of the additional species, rather than increasing the number of species per se. Therefore, the species that are best suited for inclusion into dairy pastures will be situation specific. Furthermore, the presence of additional species will generally require modification to the management of dairy pastures, particularly around nitrogen fertiliser and grazing, to ensure that the additional species remain productive and persistent.

Effects of including forage herbs in grass–legume mixtures on persistence of intensively managed pastures sampled across three age categories and five regions

ABSTRACT To test the hypothesis that the inclusion of the forage herbs chicory (Cichorium intybus L.) or plantain (Plantago lanceolata L.) or both in a grass–legume pasture mix improves persistence of sown vegetation and reduces weed and invertebrate pest ingress, a study was undertaken in 31–44 intensively managed pastures in each of five regions in New Zealand (Northland, Waikato, Bay of Plenty, Taranaki and Canterbury). The regions were stratified according to farm type (dairy or sheep and beef), pasture type (sown with grasses, legumes and herbs or grasses and legumes) and pasture age (young: 1–2 years old; medium: 3–4 years old; and old: 5+ years since sowing, n = 171). Sown species ground cover and emergence from the soil seed bank was greater, and unsown species ground cover and emergence lower, in sheep and beef pastures sown with herbs than without herbs (78% vs 68% ground cover, respectively, averaged over all pasture ages), but there was no difference between pasture types on dairy farms. Invertebrate predator and parasitoid abundance was 65% greater under pastures sown with herbs than without herbs. The number and % dry matter contribution of sown species decreased, and that of unsown species increased, as pastures aged. Unsown species comprised 90% (sheep and beef) and 98% (dairy) of total seedling emergence. The inclusion of forage herbs increased persistence of sown species and reduced weed ingress, but only on sheep and beef farms.

Effects of pasture base and species mix complexity on persistence and weed ingress in summer-dry dairy pastures

Abstract. Basal and canopy cover of sown and unsown species in swards sown with six species mixtures were assessed monthly from autumn 2010 to spring 2014, to test the hypotheses that (a) sowing an alternative pasture base, or (b) increasing the complexity of the sown mix, improves persistence and reduces weed ingress in temperate summer-dry dairy pastures. Treatments comprised either perennial ryegrass (Lolium perenne L.) infected with AR1 endophyte or tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) infected with Max P endophyte to which were added either a legume (‘standard’, 2-species mix), a legume and two forage herbs (‘herbs’, 4-species), or three legumes, two forage herbs and two grasses (‘complex’, 8-species). In the first year, basal and canopy cover of sown species were higher in perennial ryegrass- than tall fescue-based swards, and basal cover of sown species was higher and the percentage bare ground lower in the ‘standard’ (50%) than ‘herbs’ and ‘complex’ swards (42%). By the final year, basal cover of sown species (25%), unsown species (28%), and percentage bare ground (47%) were similar in all six treatments. Although establishment was greater in perennial ryegrass than tall fescue-based swards and in the ‘standard’ than in the ‘herbs’ and ‘complex’ mixtures, the loss of sown species in these treatments was greater. The decline in basal cover of sown species was –27% in the standard treatment, –16% averaged over the ‘complex’ and ‘herbs’ treatment, –24% in perennial ryegrass-based swards and –15% in tall fescue-based swards. The results are contrary to both hypotheses with respect to weed ingress. However, support was provided for the hypotheses in the greater persistence (smaller decline over time in basal cover) in tall fescue than ryegrass-based swards, and ‘herbs’ and ‘complex’ than ‘standard’ mixtures.

Effect of moisture deficit on four perennial ryegrass cultivars

The effect of moisture deficit on herbage production, root growth, tiller density, leaf appearance, percentage dry matter, and water-soluble carbohydrate (WSC) concentration and content in the stubble of Epichloe endophyte-infected perennial ryegrass plants (cultivars Aberdart AR1, Bealey NEA2, One50 AR37, Trojan NEA2) was investigated in a glasshouse study. Water was withheld from half the plants for 6 weeks, followed by a 4-week recovery period, when all plants were watered. At the end of the treatment period, there were differences among cultivars in tiller density, moisture content of the herbage, WSC content of stubble, and root mass. However, there was little effect of moisture deficit on these variables or on root depth. At the end of the recovery period, previously moisture-stressed plants had increased leaf appearance by 25%, leafy-herbage mass by 29%, and low molecular-weight WSC content of stubble by 37% compared with well watered plants, but there was a decrease in root mass in some cultivars. There were differences among cultivars in tiller density, the moisture content of the herbage and stubble WSC content. The effects of previous moisture deficit were greatest during the recovery period, and differed among cultivars, for stubble, root and total plant biomass. Results suggested that avoiding overgrazing immediately after drought is just as critical for recovery as is management during a drought, given that the greatest responses to previous moisture deficit were detected during this period.

Effect of seed mix, sowing time, summer fallow, site location and aspect on the establishment of sown pasture species on uncultivable hill country

ABSTRACT This study aimed to determine which practices resulted in the greatest establishment (plant density) of a range of grasses, legumes and herbs at four geo-climatically different hill country sites in the North Island (three sites) and South Island (one site) of New Zealand. At each site, on a north and south aspect, a seed mix containing either grasses, legumes and herbs (GLH) or legumes only (LEG), was sown in spring 2011 and autumn 2012. The 2011–2012 summer rainfall was greater than the long-term average at all sites. Establishment of total sown species was greater in the GLH than LEG mix (14% vs 8% of germinable seed sown) although some species (white clover [Trifolium repens]) established more successfully when sown in the LEG mix. Establishment was greater from spring than autumn sowing at the two wetter sites, but greater from autumn than spring sowing at the two drier sites. Greater establishment occurred after a summer fallow or summer crop than after an autumn sowing for most species at most sites. Establishment of total sown species ranged from 5%–39%, depending on the site and treatment. Seedling establishment, as a percentage of germinable seed sown, was greatest for perennial ryegrass (Lolium perenne), white clover, red clover (T. pratense) and plantain (Plantago lanceolata) (up to 36%, 37%, 33% and 35%, respectively, averaged over sites), while cocksfoot (Dactylis glomerata), phalaris (Phalaris aquatica), grazing brome (Bromus stamineus), lotus (Lotus uliginosus), birdsfoot trefoil (Lotus corniculatus) and chicory (Cichorium intybus) were below 15%.