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Abstract:The dairy industry in the southern Murray Darling Basin region of Australia is a major consumer of irrigation water because rainfall is low relative to evapotranspiration and the industrys relies heavily on irrigated temperate pastures and fodder crops. Water reforms, and potential climate change scenarios for this region suggest that there will be an overall decline in rainfall and water available for irrigation in the future. For the irrigated dairy industry to remain economically viable, there is a need for dairy farmers to improve the water productivity (WP) of their forage systems and to be able to respond to year-to-year, and within year, variation in water availability. Researchers and dairy farmers are evaluating strategies to increase WP. These include: (i) selecting better-adapted species for current and predicted climatic conditions; (ii) using species that can survive and still be productive under reduced irrigation and then recover when full irrigation is restored; (iii) modifying irrigation strategies to reduce water use whilst maintaining WP; and (iv) grazing management strategies that facilitate the survival during, and recovery after, periods of moisture stress. This review will examine these strategies and discusses their potential to optimise forage production from irrigation water inputs so that the dairy industry in the southern Murray Darling Basin remains viable in the future.

The dairy industry in Victoria, Australia, uses more than half the state’s irrigation water, mainly for growing pasture. Information on the comparative water use of forage systems would be useful for dairy farmers aiming to optimise their forage production under conditions of limited water availability. However, there are few data comparing water use under similar management and weather conditions. This paper reports on an experiment which measured and compared the production, water use, and water productivity (forage removed per unit water input) of a range of 6 border-check irrigated forage systems (3 perennial, 2 annual, and a double-cropped) and 1 spray irrigated, annual forage system, used by the dairy industry in northern Victoria. Forage removal was highest from the perennial pastures, lucerne, double-cropped and Persian clover systems in both 2005 and 2006. Irrigation water inputs in 2005 were comparable with average values reported in the literature and were closely related to the length of the growing season, with around 800–850 mm used for the perennial pastures and 340–440 mm used for the border-check irrigated annual pastures. Irrigation water inputs in 2006 were substantially higher than in 2005, reflecting the drought conditions that prevailed throughout most of Victoria, with 1100–1200 mm used for the perennial species and 450–700 mm used by the border-check irrigated annual pastures. These irrigation water requirements highlight considerable year-to-year variation as low-rainfall years are usually high-evaporation years. Irrigation water productivity (WP) was greater for the annual than for the perennial systems. In 2005, irrigation WP was 30–37 kg DM/ha.mm for the annual pastures compared with 21–27 kg DM/ha.mm for the perennial and double-cropped systems. In the drier year of 2006, irrigation WP was higher for the short-season annuals than for the other forage systems. When rainfall, runoff, and changes in soil water content were included in the calculation of total WP, there were no consistent differences in the total WP of the annual and perennial systems in either year. These findings show that under conditions of limited irrigation water availability, farmers will be able to grow more forage using winter-growing annual systems than perennial systems. However, other factors such as nutritive characteristics, cost of production, and cost of transferring feed also need to be considered when deciding which forages to grow.

Lucerne (Medicago sativa L.) has the potential to be grown widely under water-limiting conditions in the dairy region of northern Victoria and southern New South Wales, Australia, possibly because of its greater water productivity and because irrigation management of lucerne can be more flexible compared with other forage species. A large-scale field experiment was conducted at Tatura in northern Victoria, over 5 years to determine the effects of limiting (deficit) and non-limiting irrigation management on the dry matter (DM) production, water productivity (irrigation and total water productivity) and stand density (or persistence) of lucerne. Nine irrigation treatments were imposed that included full irrigation, partial irrigation and no irrigation in either a single, or over consecutive, irrigation seasons. In the fifth year of the experiment, all plots received the full irrigation treatment to examine plant recovery from the previous irrigation treatments. In any one year, there was a linear relationship between DM production and total water supply (irrigation plus rainfall plus changes in soil water) such that DM production decreased as the total water supply – due to deficit irrigation – decreased. Over the 5 years, annual DM production ranged from 1.4 to 17.7 t DM ha–1 with the highest production occurring in plots that received full irrigation. Irrigation water productivity was inversely related to the amount of water used and was higher in the treatments that had only been partially irrigated for that year compared with the treatments that had been fully watered for that year. Total water productivity values were significantly lower only in the treatments that had not been irrigated for that year, and there was little difference between the treatments that were only partially watered during the year and the fully watered treatments (range 9.1–12.2 kg DM ha–1 mm–1 for Year 4). There was no significant reduction in plant density or plant persistence in those plots where deficit irrigation had been imposed. However, the high irrigation regime and poor drainage in the fully irrigated border-check plots significantly reduced plant density and allowed weed infestation in the fifth year of the experiment. These results suggest that, although lucerne DM production is directly related to total water use and may be significantly reduced in the irrigation regions of south-eastern Australia in seasons when water is restricted, the lucerne stand is able to fully recover once a full irrigation regime is resumed. This makes lucerne an ideal forage species for situations when water is limiting.

Perennial ryegrass (Lolium perenne L.) is the predominant perennial forage species used in temperate irrigated dairy-production systems in Australia. However, when temperatures are high, even with optimal irrigation strategies and nutrient inputs, dry matter (DM) production can be compromised. This research investigated the effects of perennial ryegrass and tall fescue genotypes and summer irrigation on (DM) production and survival. Ten perennial ryegrass cultivars, three hybrid ryegrasses and two cultivars of tall fescue (Festuca arundinacea (Schreb) Darbysh.) were sown in northern Victoria, Australia, in May 2014, and were managed under full irrigation or restricted irrigation (no irrigation between late December and mid-March) over a 3-year period. Measurements included net pasture accumulation (DM production), sward density (plant frequency) and water-soluble carbohydrate concentration. Apart from the expected differences in DM yield over the summer period between full irrigation and restricted irrigation, there were few differences in DM production among perennial ryegrass or tall fescue cultivars. Plant frequency declined significantly under restricted irrigation in Years 2 and 3 compared with full irrigation but there were no differences among perennial ryegrass cultivars. In Year 2, plant frequency was higher in the tall fescue cultivars than the ryegrass cultivars. The recovery pattern in DM production following recommencement of irrigation in mid-March (autumn) varied across years. In Year 1, plants recovered rapidly once irrigation recommenced in autumn. However, in Years 2 and 3, autumn and winter pasture accumulation under restricted irrigation was 30–35% less than under full irrigation. These differences were possibly related to decreases in plant frequency, as well as to differences in the amounts of residual pasture mass (or carbohydrate reserves) present when growth ceased. Analyses of the water-soluble carbohydrate concentrations in the pseudostem during summer and autumn in Year 3 showed differences in total water-soluble carbohydrate and in fructan and sucrose concentrations between irrigation treatments but no consistent differences among genotypes.