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Reliability of higher seeding rates of wheat for increased competitiveness with weeds in low rainfall environments

Published online by Cambridge University Press:  10 January 2005

D. LEMERLE ,
R. D. COUSENS ,
G. S. GILL ,
S. J. PELTZER ,
M. MOERKERK ,
C. E. MURPHY ,
D. COLLINS  and
B. R. CULLIS
D. LEMERLE
Affiliation:
Co-operative Research Centre for Weed Management Systems, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia Wagga Wagga Agricultural Institute, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia
R. D. COUSENS
Affiliation:
Co-operative Research Centre for Weed Management Systems, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia School of Resource Management, Institute of Land and Food Resources, The University of Melbourne, Victoria 3010, Australia
G. S. GILL
Affiliation:
Co-operative Research Centre for Weed Management Systems, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia School of Agriculture and Wine, The University of Adelaide, Roseworthy, SA 5371, Australia
S. J. PELTZER
Affiliation:
Co-operative Research Centre for Weed Management Systems, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia Agriculture Western Australia, 444 Albany Highway, Albany 6330, Australia
M. MOERKERK
Affiliation:
Department of Primary Industries, Victorian Institute of Dryland Agriculture, Private Bag 260, Horsham, Victoria 3401, Australia
C. E. MURPHY
Affiliation:
Co-operative Research Centre for Weed Management Systems, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia Present address: Office of Gene Technology Regulator, PO Box 100 Woden ACT 2606, Australia.
D. COLLINS
Affiliation:
Elizabeth Macarthur Agricultural Institute, Woodbridge Road, Menangle NSW 2568, PMB 8 Camden 2570, Australia
B. R. CULLIS
Affiliation:
Wagga Wagga Agricultural Institute, NSW Agriculture, PMB, Wagga Wagga, NSW 2650, Australia
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Abstract

Increasing crop competitiveness using higher seeding rates is a possible technique for weed management in low input and organic farming systems or when herbicide resistance develops in weeds. A range of wheat seeding rates were sown and resulted in crop densities between 50–400 plants/m2 (current recommendations are 100–150 plants/m2) in the presence and absence of annual ryegrass (Lolium rigidum Gaud.) in three wheat cultivars at nine experiments in southern Australia. Wheat densities of at least 200 plants/m2 were required to suppress L. rigidum and to a lesser extent increase crop yield across a wide range of environments (seasonal rainfall between 200–420 mm) and weed densities (50–450 L. rigidum plants/m2). Doubling crop density of all cultivars from 100 to 200 plants/m2 halved L. rigidum dry weight (averaged over all experiments) from 100 g/m2 to about 50 g/m2. Higher crop densities gave diminishing marginal reductions in weed biomass, while cultivar differences in weed suppression were small. Grain yields ranged from 0·5 t/ha to over 5 t/ha depending on site and season. Maximum yields in the weed-free plots (averaged over environments and cultivars) were at 200 crop plants/m2, and yield declined only slightly by 4–5% at densities up to 425 plants/m2. In the weedy plots grain yield continued to increase up to the highest density but at a slower rate. The percentage yield loss from weed competition was of a smaller magnitude than the suppression of L. rigidum by wheat. For example, 100 wheat plants/m2 led to an average 23% yield loss compared with 17% at 200 plants/m2, and the probability of reduced crop grain size and increased proportion of small seeds was negligible at these densities. Cultivar differences in yield loss from weed competition were small compared with differences due to crop density. Adoption of higher wheat seed rates as part of integrated weed management is now strongly promoted to farmers.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 142 , Issue 4 , August 2004 , pp. 395 - 409
Copyright
2004 Cambridge University Press

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