Ground Cover South : Ground Cover 049 April-May 2004 - South
RESEARCH UPDATE 11 APRIL 2004 CANOPY MANAGEMENT ��� ����� ��� ������� ������ ����� ����� ������ ������ �������� � ���� � ���� ���� �� ��� ������������� ������ ���� ������������� ������� ������ ��� �������� ������� ������� ����� ��������� ����������� �� ������� ������� � ���������� ����� �������� �������� ����� ��� �� � ���� �������� ������ ��� ���� ������� ������� ���� ����������� ����� ������� ��������� ��� ������������ ��� �������� ���� ��� ��� ���� � ��� ������ �� ������ ������� ��� ����� ��� ������� � ���� ��� �������� ����������� ���������� �������� ��� ����������� ��������� ������� ��� ���� ����� ���� �� ����������� ���� ���������� ������� � ��� ��� ����� ���� �� ��� ������ ������� ��������� ��� ��� ��� �� ����� ������� �������� ���� � ������������ ������ � ������ �������� � ���������� � ���� ������ ����� ����� �� ����� ���� ��� ����� ���� ����� ������� ������������ ������� ���� ��������� By EAMMON CONAGHAN Decades separate some areas of the WA wheatbelt where sheep were last seen, and in the intervening years the ryegrass (diet of those now rare creatures) has developed an appetite of its own, chomping into wheat yields with the same voracity with which it was once consumed. Ryegrass is the leading threat confronting WA growers as they fght their share of Australia’s $3 billion- a-year weed war. With sheep gone, and no tillage sparing ryegrass the ‘harrowing’ experience, researchers are busy seeking out alternatives to the near exhausted herbicide option. The WA Department of Agriculture’s Dr Abul Hashem believes the method of sowing a crop may hold the key to ‘stitching up’ ryegrass. “The uniform distribution of wheat seeds via cross sowing can minimise competition between wheat plants, while increasing their competition against ryegrass weeds, which fourish between rows in traditional seeding regimes,” he says. During cross seeding, half of the seed is deposited in one direction and the balance in a second pass, at a right angle. The fertiliser is applied equally in each direction. Working with Catherine Borger and Glen Riethmuller, Dr Hashem experimented with the technique at Merredin in 1997 before adding trifuralin at seeding with subsequent trials in Merredin (1999, 2000, 2003) and Mullewa (2000, 2003). The criss-cross seeding pattern worked its magic, with ryegrass biomass falling 14 to 32 percent in Merredin and almost 30 percent in Mullewa. “Cross seeding limited ryegrass growth and ultimately dropped ryegrass seed production by an average of 37 percent compared with conventional seeding,” Dr Hashem explains. “Trifuralin was also effective, with ryegrass seed production falling 61 percent with its incorporation, regardless of the seeding technique used. “When combining cross- seeding and trifuralin, ryegrass seed production was lowered by as much as 85 percent.” Apart from this impressive record of ryegrass inhibition, the ultimate test of the technique was, of course, cereal production come harvest time. Did cross- seeding raise wheat yield? Throughout the study, cross-seeding wheat with trifuralin lifted wheat yield by 10 to 23 percent on the back of an 8 to 30 percent crop biomass increase. “Cross seeding can be added to a grower’s weed control armoury as a non- chemical alternative, or used in association with trifuralin,” Dr Hashem concludes. “When working with a Kellerberrin paddock suffering from a high resistant ryegrass weed burden, this technique drove yield up by 500 kilogram per hectare.” Several oaten hay producers in WA’s southern wheatbelt have adopted cross seeding because it allows them to sow at rates of 150 to 170 kg/ha, which cannot be delivered in a single pass. This helps produce softer hay, which is more palatable to stock. GRDC PROGRAM 3 For more information: Dr Abul Hashem, DAWA, 08 9690 2187, firstname.lastname@example.org BY EMMA LEONARD Wheat growing in the United Kingdom is a world away from cropping practices in Australia – too little sun versus too little water for starters – but farmers in both hemispheres are still dealing with the same plant and its physiological needs. For this reason, a visiting specialist in crop canopy management, Professor Roger Sylvester-Bradley from the UK rural research consultancy ADAS and the University of Nottingham, believes lessons learned by UK farmers could be of use in Australia. He says canopy management means ensuring the crop is in the proper condition during the yield formation period. In the UK this means trying to achieve a slow nitrogen uptake to overcome the UK’s main yield limiter – lack of sunshine. In the UK, wheat is predominantly grown on heavy fertile soils in the east, where nitrogen is the only limiting nutrient. The days are long, but there is 60 to 70 percent cloud cover. Average yields are eight tonnes per hectare for autumn sown wheats, which take 200 days to reach stem elongation and a further 100 days to maturity. He says the UK’s main crop performance limitation is insuffcient solar radiation – the capture of light to drive photosynthesis and build energy stores. This is very different to most of the grain growing areas of Australia where effective rainfall rather than sunshine is generally the hurdle to jump. However, Professor Sylvester-Bradley believes the UK experience can still help Australian growers better condition their crops during yield formation. “Our objective is to optimise and maintain green leaf area per unit of ground area, expressed as the Green Area Index (GAI) to maximise light capture,” he explains. “To do this we want to advance canopy closure and delay crop senescence (ageing) but we don’t want to create too much green leaf, otherwise too much energy is going into structure and not construction of yield.” To achieve an 8t/ha wheat yield in the UK, a GAI of six is required and this achieves 94 percent light capture. By the same rules, a 4t/ha yield grown under Australian conditions would only require a GAI of about 4.2 and this would achieve 88 percent light capture. This would suggest that many Australian crops have excessive canopies for the lower yielding conditions here. To produce target canopy cover, many UK growers have reduced seeding rates to achieve the optimum 60 plants per square metre for early autumn sown crops and 140 plants/m2 for late autumn sown crops, and have coupled this with tactical nitrogen management. “In the UK we have a very reliable relationship between deep nitrogen measurements taken in February and nitrogen availability to the following crop,” says Professor Sylvester-Bradley. “This underpins the calculation of the crop’s nitrogen requirement. We know that for every unit of GAI we need 30kg/ha of available nitrogen. “By multiplying our target GAI – 6 by 30kg/ha – we know our crops’ nitrogen requirement is 180kg N/ha. “From my research I feel this assumption would also hold true in Australian conditions,” he says. “To calculate the crops fertiliser N requirement, we subtract the soil N from the 180kgN/ha and divide the result by 60 percent (as fertiliser is only 60 percent effcient) to give the requirement for canopy construction.” In the UK the aim is to apply 60 to 70 percent of nitrogen requirement by the formation of the frst node, the remaining 30 to 40 percent by the second node. Additional nitrogen is provided after fowering to build grain protein. “We are aiming to have a slow uptake of nitrogen throughout the growth of the crop which can take over 300 days from sowing to maturity,” says Professor Sylvester-Bradley. “In UK conditions smaller more frequent applications of nitrogen help achieve this and keep inputs in line with projected yield.” He also says that this tactical use of nitrogen and managed canopy growth not only helps yield directly, but also indirectly through reduced disease and crop lodging. He says the only downside is the need for more management effort, but in the future this may be minimised through precision agricultural technology. For more information: Professor Roger Sylvester- Bradley, email@example.com Cross seeding enlisted in the weed war Reduce foliage, increase yield n UK lessons may be of use in Australia n Objective is to maximise light capture n Too much green leaf can reduce construction of yield n Many Australian crops may have excessive canopies n To achieve target canopies, reduce seeding rates coupled with tactical N management WEED CONTROL English lessons: Professor Roger Sylvester-Bradley from ADAS UK (centre) with Peter Hooper from the University of Adelaide (left) and Charlie Walker from Incitec Pivot.
Ground Cover 050 June-July 2004 - South
Ground Cover 048 February-March 2004 - South