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Suppression of lolium rigidum in wheat by cultural means

R.W. Medd, B.A. Auld and D.R. Kemp

Agricultural Research and Veterinary Centre, Orange 2800

Agronomy "packages" for broadacre wheat production are mostly derived from experiments done under weed-free conditions. Yet cultural operations which give maximal grain yield may not necessarily be optimal under weedy conditions. The experiments reported compared wheat grain yields when L. rigidum was grown with wheat sown in varying densities and spatial arrangements.


Four field experiments located near Manildra N.S.W. were conducted over the climatically contrasting seasons 1978 to 1980. Wheat cv. Condor was sown in poisson (traditional), precisely square and rectangular2arrangements using drilled boards at densities of 40, 74 and 200 plants m . L. rigidum was oversown intq the top 40 mm of plots to give populations of from zero to 300 plants m Data presented here are for wheat grain yields.

Results and Discussion

Mean weed-free wheat grain yields varied between years from 1.3 to 5.4 t ha-1 but the proportional effects of L. rigidum competition were similar across experiments. The results from each experiment have been combined as given in Table 1.

Table 1. Effect of L. rigidum on wheat grain yield: figures are means across experiments of grin yield as percent of highest yielding treatment within each experiment (- SE of mean).

As the density of L. rigidum increased, wheat grain yields in low density crops decreased to a similar extent in square and rectangular arrangements. The depression of wheat yields was significantly greater in the poisson arrangement.

Wheat grain yield in crops at 200 plants m-2 was less affected by L. rigidum and grain yield was significantly reduced only by 101 to 300 plants m in the rectangular arrangement.

The highest wheat density tested also greatly reduced the mean plant weight of L. rigidum (1). It therefore seems advisable to increase crop density, rather than vary arrangement, to reduce the competitive effects of L. rigidum.

1. Medd, R.W, Auld, B.A. and Kemp D.R. 1981. Proc. 6th Aust. Weeds Conf. 1:39-43.

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