Estimates indicate that 30% of land surface globally is affected by soil acidity, influencing agricultural production. Application of lime increases soil pH and improves crop growth. We tested the hypothesis that liming will reduce rigid ryegrass (Lolium rigidum Gaudin) growth by improving the competitive ability of the crop. Experiments at Merredin and Wongan Hills in Western Australia indicated that application of lime in previous years reduced L. rigidum density, biomass, and seed production in wheat (Triticum aestivum L.) crops in 2018. At Merredin, L. rigidum seed production in 2018 was reduced from 9,390 to 2,820 seeds m−2, and wheat tiller number and yield was increased, following lime application of 0 to 6,000 kg ha−1 in 2016. At Wongan Hills, lime application of 4,000 kg ha−1 in 1994 reduced seed production in the 2018 wheat crop from 4,708 to 1,610 seeds m−2, and application of 3,000 kg ha−1 of lime in 2014 reduced seed production from 3,959 to 921 seeds m−2 in 2018. Again, lime increased wheat tiller number, but not yield. A screen house experiment (in controlled conditions) indicated that lime application increased the initial growth of both L. rigidum and wheat seedlings. This supports the conclusion that reduced L. rigidum growth and seed production in the field resulted from increased competitive ability of the crop, rather than any direct and detrimental impact of lime on L. rigidum growth. Incorporation of lime reduced initial emergence of L. rigidum in controlled conditions, with L. rigidum seeds at a uniform depth, and in the field experiments in situations of high weed density, with seeds buried by the incorporation process. Nationally, the revenue loss from residual L. rigidum in crop is A$93 million per year. The current research confirms that application of lime will increase the competitive ability of crops growing in regions with acidic soils.