Ground Cover West : Ground Cover 066 January-February 2007 - West
JANUARY -- FEBRUARY 2007 GROUND COVER 29 Weather: western zone HARVEST RADIO www.grdc.com.au/radio/main.htm Highest on record Very much above average Above average Average Below average Very much below average Lowest on record 10 8-9 4-7 2-3 1 TEMPERATURE DECILES RANGES Another dry year for the cropping zone BY DR ANDREW WATKINS AND DR BLAIR TREWIN National Climate Centre, Bureau of Meteorology n Australia was dominated by the impacts of El Niño and longer-term climate change during 2006. Although the Pacific Ocean did not reach full El Niño status until spring, its development was associated with a build- up of higher than normal pressures over the continent from May onwards, effectively keeping cold fronts to the south of the continent and suppressing cloud formation over the interior. The clear skies also led to slightly warmer days and cool nights. Rainfall for southern Australia’s main crop and pasture growing season (April to October) was generally very low, with virtually the entire cropping region suffering below-average rainfall (Figure 1). Total rainfall over the GRDC’s three cropping regions was 163 millimetres, the sixth driest since high-quality monthly rainfall records started in 1900. It was only drier in the cropping regions during the El Niño-related droughts of 1994, 1982, 1902, 1940 and 2002. For the southern region it was the fourth driest season on record (157mm), behind 1914 (the driest), 1982 and 1902, while in the western zone it was the third driest (184mm) behind 1914 (the driest) and 1940. These dry conditions were exacerbated by daytime maximum temperatures (Figure 2) that were fourth highest on record, with maximums 1.1°C above average over the cropping regions. In contrast, nights were cool, with minimums over the cropping regions 0.3°C below the 1961–90 mean. As a result, the mean cropping region temperature was 0.4°C above normal, ranking it 15th, alongside such years as 1987 and 2001. Similar values and ranking were observed UNDERSTANDING WATER-USE EFFICIENCY BY VICTOR SADRAS (SARDI) AND JOHN ANGUS (CSIRO) n At the end of the season, many graingrowers and agronomists calculate water- use efficiency to determine how effective they were in turning water into grain. However, a worldwide comparison has indicated that care should be taken when interpreting water-use efficiencies of 10kg grain per hectare per millimetre of rainfall as evidence of poor management. Instead, in the context of water scarcity and increasing environmental pressure, a broader benchmark may be useful. Is the low water-use efficiency typical of these crops or a local problem? How does the water-use efficiency of wheat in south-eastern Australia compare with other dry environments? To answer these questions, we compared the water-use efficiency of wheat in south- eastern Australia with that of crops grown in dry regions of the world, including the North American Great Plains, China’s Loess Plateau and the Mediterranean basin. Severe water deficit in the critical stages of flowering, grain set and filling is a common feature of all four environments. In the 1980s, French and Schultz plotted grain yield and water use for wheat grown in SA, finding that most crops fell beneath 20kg grain/ha/mm. Our research indicated that an updated French & Schultz line provides a sound ‘envelope’ for the wheat crops in all four regions. This indicates that the water-use efficiency of wheat in Australia compares well with those in other dry regions. The gap between actual and attainable yield is not a local problem, but a widespread feature of dryland cropping systems. Water-use efficiency, expressed as the ratio of grain yield and water use, had an absolute maximum of 22.3kg grain/ha/mm, but few crops actually reached ratios close to this value. Average water-use efficiency was 9.9kg/ha/mm for south-eastern Australia, 9.8kg/ha/mm for China’s Loess Plateau, 8.9kg/ha/mm for the northern Great Plains of North America, 7.6kg/ha/mm for the Mediterranean basin, and 5.3kg/ha/mm for the southern-central Great Plains. These represent 31 to 44 per cent of the maximum estimated for these environments. Once the effect of evaporative demand is taken into account, the average efficiency is in line for all regions. This again indicates that the gap between actual and potential water use efficiency is not a local Australian problem, but a likely consequence of factors typical of dry environments. These include: n Massive water losses through soil evaporation. FIGURE 2 : MAXIMUM TEMPERATURE DECILES (1950--PRESENT) 1 April to 31 October 2006 in the three cropping regions, although the southern region experienced its coldest nights since the records began in 1950, with minimums averaging 0.9°C below normal. The clear skies and very low soil moisture brought severe frosts to many areas in all three GRDC cropping regions during late May and mid-June, with many record low temperatures recorded, including –6.8°C at Stanthorpe, Queensland, –7.5°C at Rutherglen, Victoria, –1.3°C at Perth Airport and –10.5°C at Liawenee, Tasmania. Severe frosts also occurred across south-eastern Australia in late September and mid-October, causing widespread crop losses. The dry conditions of 2006 were not isolated, and need to be viewed in the context of the longer-term climate. The five years to October 2006 were the driest such five-year period on record over the cropping zone, with 2042mm in total falling for the 60 months to October 2006, against the long-term five-year average of 2376mm. Second to fourth, and sixth and seventh- placed 60-month rainfall totals ending October all occurred in the 1940s, while fifth ranked was 1900–1905, which included the last years of the Federation drought. The five years to October 2006 were also the warmest such period on record, with mean temperatures 0.5°C above the 1961–90 mean, and daytime maximums warmest on record, 0.9°C above the average. The second warmest such period was the 60 months to October 2005. Early predictions for 2007 suggest a peak in the El Niño early in the year, with computer models suggesting a return towards more neutral conditions around autumn. More information: Dr Andrew Watkins, email@example.com; Dr Blair Trewin, firstname.lastname@example.org n Timing of rainfall constraining sowing opportunities and the critical physiological process of grain set and filling. n High evaporative demand during flowering and grain fill. Our research shows that water-use efficiency of wheat crops in south-eastern Australia is in line with efficiencies measured in comparable environments on a global scale. The fact that crops rarely reach their potential efficiency is mostly related to environmental constraints typical of dry environments. Although good management practices are necessary, they may be insufficient to achieve high water-use efficiency in dry environments. Management practices could aim at improving the water use efficiency of single crops, to improve the efficiency of the whole-farming system, or both. Both are important, but larger gains are expected from management at the farming system level. At the crop level, practices to improve water use efficiency include timely sowing, management of weeds and stubble, and better matching of resources, chiefly water and nutrients. Fertiliser management is particularly important in systems where the high risk of farming associated with uncertain rainfall is tackled with a low-input strategy. At the farm level, large gains in productivity and efficiency in the use of resources are likely to derive from cropping intensification. Greater diversity and intensity of cropping at the expense of fallow and pastures is possible in agro- ecosystems of south-eastern Australia where wheat-fallow and wheat-pasture rotations have been dominant. Source: Sadras VO, Angus JF (2006) Benchmarking water use efficiency of rainfed wheat in dry environments. Australian Journal of Agricultural Research 57, 847--856 More information: Associate Professor Victor Sadras, 08 8303 9661, email@example.com; John Angus, 02 6246 5095, firstname.lastname@example.org Highest on record Very much above average Above average Average Below average Very much below average Lowest on record 10 8-9 4-7 2-3 1 RAINFALL DECILES RANGES FIGURE 1: AUSTRALIAN RAINFALL DECILES 1 April to 31 October 2006 SOURCE: BOM 6 5 4 3 2 1 0 n=691 0 100 200 300 400 500 600 Water use (mm) China's Loess Plateau Mediterranean Basin North American Great Plains SE Australia SOURCE: BOM Figure 1. Relationship between wheat grain yield and water use in four dry regions of the world. The line represents 22kg/ha/ mm, and a zero-yield point at 60mm. Data for low- rainfall regions of south- eastern Australia include most of the agricultural regions of South Australia, the Mallee regions of SA, Victoria and NSW, and the Victorian Wimmera.
Ground Cover 065 November-December 2006 - West
Ground Cover 067 March-April 2007 - West