Kg Pembleton

Giving drought the cold shoulder: a relationship between drought tolerance and fall dormancy in an agriculturally important crop

Fall dormant/freezing tolerant plants often also exhibit superior tolerance to drought conditions compared to their non-fall dormant/freezing intolerant counterparts. This experiment aimed to investigate this phenomenon in an agriculturally important crop. Seven alfalfa cultivars with varying levels of fall dormancy/freezing tolerance were exposed to a water deficit. The more fall dormant cultivars had superior tolerance to a mild water deficit. Two genes, CAS18 (encodes for a dehydrin like protein) and CorF (encodes for a galactinol synthase), were up regulated in association with this drought tolerance. Both these genes are early response genes, providing clues to the stress signalling pathways involved.

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.

Yield and water-use efficiency of contrasting lucerne genotypes grown in a cool temperate environment

In Tasmania, Australia, forage production is maximised by the use of irrigation. However, availability of water for irrigation is often limited, making the water-use efficiency (WUE) of a species/genotype an important consideration when designing forage systems. Field experimentation and an associated modelling study was undertaken to determine the WUE and environmental factors influencing WUE for contrasting lucerne (Medicago sativa) genotypes across six dairying regions within Tasmania. In the field experiment a significant genotype influence on WUE was identified under irrigated conditions and modelling identified a genotype influence on WUE in three out of six regions. WUE was related to the amount of water received (irrigation plus rainfall). The marginal response to the application of irrigation water (MWUE) was greatest for the highly winter-active genotype in the field experiment; however, modelling did not identify a consistent genotype influence on MWUE across regions. MWUE was negatively associated with the amount of deep drainage. The present study identified that lucerne has the potential to improve the WUE of forage systems across six different Tasmanian regions. The linkage of MWUE and deep drainage highlights that deficit irrigation practices could further improve the WUE of this forage crop, particularly in environments prone to deep drainage.

Opportunities and challenges in Australian grasslands: pathways to achieve future sustainability and productivity imperatives

Abstract. Grassland production systems contribute 40% to Australia’s gross agricultural production value and utilise >50% of its land area. Across this area, diverse systems exist, but these can be broadly classified into four main production systems: (i) pastoral grazing, mainly of cattle at low intensity (i.e. <0.4 dry sheep equivalents/ha) on relatively unimproved native rangelands in the arid and semi-arid regions of northern and central Australia; (ii) crop–livestock systems in the semi-arid zone where livestock graze a mixture of pastures and crops that are often integrated; (iii) high-rainfall, permanent pasture zone in the coastal hinterland and highlands; and (iv) dairy systems covering a broad range of environments and production intensities. A notable trend across these systems has been the decline in sheep numbers and the proportion of income from wool, with beef cattle or sheep meat increasingly important. Although there is evidence that most of these systems have lifted production efficiencies over the past 30 years, total factor productivity growth (i.e. change in output relative to inputs) has failed to match the decline in terms of trade. This has renewed attention on how research and development can help to increase productivity. These industries also face increasing scrutiny to improve their environmental performance and develop sustainable production practices. In order to improve the efficiency and productivity of grassland production systems, we propose and explore in detail a range of practices and innovations that will move systems to new or improved states of productivity or alter efficiency frontiers. These include: filling gaps in the array of pastures available, either through exploring new species or improving the adaptation and agronomic characteristics of species currently sown; overcoming existing and emerging constraints to pasture productivity; improving livestock forage-feed systems; and more precise and lower cost management of grasslands. There is significant scope to capture value from the ecological services that grasslands provide and mitigate greenhouse gas emissions from livestock production. However, large reductions in pasture research scientist numbers (75–95%) over the past 30 years, along with funding limitations, will challenge our ability to realise these potential opportunities.

Evaluating the accuracy of the Agricultural Production Systems Simulator (APSIM) simulating growth, development, and herbage nutritive characteristics of forage crops grown in the south-eastern dairy regions of Australia

Abstract. Pasture-based dairy farms are a complex system involving interactions between soils, pastures, forage crops, and livestock as well as the economic and social aspects of the business. Consequently, biophysical and farm systems models are becoming important tools to study pasture-based dairy systems. However, there is currently a paucity of modelling tools available for the simulation of one key component of the system—forage crops. This study evaluated the accuracy of the Agricultural Production Systems Simulator (APSIM) in simulating dry matter (DM) yield, phenology, and herbage nutritive characteristics of forage crops grown in the dairy regions of south-eastern Australia. Simulation results were compared with data for forage wheat (Triticum aestivum L.), oats (Avena sativa L.), forage rape (Brassica napus L.), forage sorghum (Sorghum bicolor (L.) Moench), and maize (Zea mays L.) collated from previous field research and demonstration activities undertaken across the dairy regions of south-eastern Australia. This study showed that APSIM adequately predicted the DM yield of forage crops, as evidenced by the range of values for the coefficient of determination (0.58–0.95), correlation coefficient (0.76–0.94), and bias correction factor (0.97–1.00). Crop phenology for maize, forage wheat, and oats was predicted with similar accuracy to forage crop DM yield, whereas the phenology of forage rape and forage sorghum was poorly predicted (R2 values 0.38 and 0.80, correlation coefficient 0.62 and –0.90, and bias correction factors 0.67 and 0.28, respectively). Herbage nutritive characteristics for all crop species were poorly predicted. While the selection of a model to explore an aspect of agricultural production will depend on the specific problem being addressed, the performance of APSIM in simulating forage crop DM yield and, in many cases, crop phenology, coupled with its ease of use, open access, and science-based mechanistic methods of simulating agricultural and crop processes, makes it an ideal model for exploring the influence of management and environment on forage crops grown on dairy farms in south-eastern Australia. Potential future model developments and improvements are discussed in the context of the results of this validation analysis.

Yield, yield components and shoot morphology of four contrasting lucerne (Medicago sativa) cultivars grown in three cool temperate environments

Understanding which component has the greatest influence on yield is vital when managing lucerne (Medicago sativa) crops to maximise the production of high-quality forage. However, both yield components and plant morphology are affected by interactions between environment conditions and plant genetics. Field experiments across three environments (dryland at Cambridge: 500 mm annual rainfall, brown sodosol soil type; dryland at Elliott: 1200 mm annual rainfall, red ferrosol soil type; and irrigated at Elliott) in Tasmania, Australia were undertaken to investigate the yield, yield components and plant morphology of four lucerne cultivars; DuPuits, Grasslands Kaituna, SARDI 7 and SARDI 10 under cutting. The effect of cultivar on dry matter (DM) yield was different in each environment, with Grasslands Kaituna achieving the highest yield (P 0.05) occurred under irrigation. Stepwise linear regression consistently confirmed mass per shoot as the yield component with the greatest influence on DM yield for all cultivars and environments. Shoot density also had an influence on DM yield in two of the three environments. DuPuits had the highest leaf : stem ratio in all three environments and slower morphological development in two of the environments. Management practices across all environments and cultivars should aim to increase mass per shoot to maximise yield. Of the cultivars examined Grasslands Kaituna is the most appropriate for dryland conditions in Tasmania, while all cultivars examined were suited to production under irrigation.

More milk from forage: Milk production, blood metabolites, and forage intake of dairy cows grazing pasture mixtures and spatially adjacent monocultures

There is interest in the reincorporation of legumes and forbs into pasture-based dairy production systems as a means of increasing milk production through addressing the nutritive value limitations of grass pastures. The experiments reported in this paper were undertaken to evaluate milk production, blood metabolite concentrations, and forage intake levels of cows grazing either pasture mixtures or spatially adjacent monocultures containing perennial ryegrass (Lolium perenne), white clover (Trifolium repens), and plantain (Plantago lanceolata) compared with cows grazing monocultures of perennial ryegrass. Four replicate herds, each containing 4 spring-calving, cross-bred dairy cows, grazed 4 different forage treatments over the periods of early, mid, and late lactation. Forage treatments were perennial ryegrass monoculture (PRG), a mixture of white clover and plantain (CPM), a mixture of perennial ryegrass, white clover, and plantain (RCPM), and spatially adjacent monocultures (SAM) of perennial ryegrass, white clover, and plantain. Milk volume, milk composition, blood fatty acids, blood β-hydroxybutyrate, blood urea N concentrations, live weight change, and estimated forage intake were monitored over a 5-d response period occurring after acclimation to each of the forage treatments. The acclimation period for the early, mid, and late lactation experiments were 13, 13, and 10 d, respectively. Milk yield (volume and milk protein) increased for cows grazing the RCPM and SAM in the early lactation experiment compared with cows grazing the PRG, whereas in the mid lactation experiment, milk fat increased for the cows grazing the RCPM and SAM when compared with the PRG treatments. Improvements in milk production from grazing the RCPM and SAM treatments are attributed to improved nutritive value (particularly lower neutral detergent fiber concentrations) and a potential increase in forage intake. Pasture mixtures or SAM containing plantain and white clover could be a strategy for alleviating the nutritive limitations of perennial ryegrass monocultures, leading to an increase in milk production for spring calving dairy cows during early and mid lactation.

Quantifying the interactions between grazing interval, grazing intensity, and nitrogen on the yield and growth rate of dryland and irrigated perennial ryegrass

Abstract. In temperate regions of Australasia, feed-base management is the key determinant of the economic viability of dairy enterprises. However, conjecture exists regarding agreed grazing management practices for pasture-based dairy systems, because of the combined effects of variable seasonal conditions and input management (irrigation and nitrogen (N) usage). To address this conjecture a 2-year defoliation study was undertaken in the high-rainfall zone of north-western Tasmania, to examine the effect of these interactions on the yield of perennial ryegrass (Lolium perenne L.) dominated pasture. Treatments were imposed in a split-split-plot design with moisture availability the main plot treatment (irrigated or dryland), defoliation intervals (full emergence of 1, 2, or 3 new leaves/tiller) assigned to subplots, and both defoliation intensity (30, 55 and 80 mm) and N application rate (0.0, 1.5 and 3.0 kg N/ha.day) treatments crossed within sub-subplots. Although the independent effects of each treatment on total yield were significant (P < 0.05), the effect of N application was found to diminish with time (P < 0.05). Furthermore, under periods of high pasture growth resulting from the absence of moisture stress (irrigation), shortening the grazing rotation via defoliating at the second leaf stage had no detrimental impact on growth rates. However, to optimise growth rates during periods of either soil moisture deficits or low temperatures, longer rotation lengths (to the 3-leaf stage) were required. High response rates to N fertiliser were found during the initial (first 6 month) period of this 2-year study; however, these responses diminished with time, with plots receiving zero N fertiliser achieving growth rates comparable to those plots that received rates as high as 3 kg N/ha.day.

Genotype by environment interactions of lucerne ( Medicago sativa L.) in a cool temperate climate

Genotype by environmental interactions in lucerne (Medicago sativa L.) present considerable challenges when selecting an appropriate cultivar for a particular location and farming system. Data on the yield and persistence of a range of lucerne cultivars and experimental lines grown in two Tasmanian environments, Forth (41.20°S, 146.27°E, Red Ferrosol soil, under cutting with high fertiliser inputs, i.e. a high yield potential environment) and Cranbook (42.00°S, 148.03°E, Red Ferrosol soil, under grazing with low fertiliser inputs, i.e. a low yield potential environment) were examined using winter activity class as the experimental factor. At Forth, winter-dormant lucernes were the lowest yielding genotypes. In contrast, at Cranbrook, highly winter-active genotypes had lower plant persistence and dry matter yield than winter-dormant genotypes. Modified joint linear regression analysis showed that in a cool temperate climate, winter-dormant genotypes are more suited to a low yield potential environment, whereas highly winter-active genotypes are adapted to a high yield potential environment. Both the semi-winter-dormant and the winter-active genotypes were adapted to all environments. The dry matter yield of winter-dormant and highly winter-active genotypes was most sensitive to environmental conditions in winter and spring, while performance of all cultivars and experimental lines was most stable over summer.

Effect of summer irrigation on seasonal changes in taproot reserves and the expression of winter dormancy/activity in four contrasting lucerne cultivars

In the summer dry environment of cool temperate Tasmania, summer irrigation is used to maximise forage production. For lucerne (Medicago sativa L.) this irrigation is likely to interact with winter-dormancy genotypes to influence seasonal changes in taproot reserves and thus, the process of cold acclimation. To test this hypothesis four lucerne cultivars with contrasting levels of winter dormancy (DuPuits: winter-dormant; Grasslands Kaituna: semi winter-dormant; SARDI 7: winter-active: SARDI 10, highly winter-active) were grown in small plots at Elliott, Tasmania, under irrigated or dryland conditions. At each defoliation taproots were sampled and assayed for the concentration of soluble sugars, starch, amino acids, soluble protein, the abundance of vegetative storage proteins (VSP), and the abundance of mRNA transcripts associated with cold acclimation and VSP. Taproot-soluble protein concentrations in DuPuits significantly increased from summer to autumn when plants were grown under dryland conditions. When grown under irrigated conditions, taproot-soluble protein concentrations decreased over summer and increased in autumn for all cultivars. The abundance of VSP increased in summer in all cultivars grown under dryland conditions. Taproot-soluble sugar concentrations increased and starch decreased in autumn for all cultivars grown under both water regimes. Plants grown under dryland conditions showed little change in RNA transcript abundance of cold acclimation genes across all cultivars and sampling dates, while in those plants grown under irrigated conditions, transcript abundance was influenced by sampling date, and for some genes, by cultivar. There was a clear carry-over effect from the exposure of summer drought on the winter-dormancy response. The expression of winter dormancy at an agronomic and molecular level was greater under dryland conditions.