The effects of suppressing couch grass (Elytrigia repens L.), through integrated management, on soil biological quality and N and P nutrition of barley (Hordeum vulgare L.) were evaluated in a field experiment (1987–92) on a Dark Grey soil in Alberta, Canada. The management practices consisted of combinations of herbicide application, crop rotations and tillage treatments. The 3-year crop sequences consisted of continuous barley, canola (Brassica rapa L.)–barley–barley, fallow–barley–barley, and barley or canola undersown with red clover (Trifolium pratense L.)–red clover green manure–barley. In 1992, the sixth year of the experiment, soil and plant samples were analysed for nutrient content. Treatments that consisted of spring and autumn tillage only did not suppress couch grass and produced low barley yields and N and P uptake. More N was immobilized in couch grass shoots and rhizomes and soil microbial biomass with these treatments than with similar herbicide-treated crop rotations. Tillage-plus-herbicide treatments effectively suppressed couch grass and enabled the barley crop to compete for soil N, however, both spring and autumn tillage were required for weed control. The fallow treatment impaired soil quality by reducing soil and microbial C and N, but produced similar barley yields as continuous cropping with tillage-plus-chemical control. Red clover ploughed in for green manure enhanced soil quality indicators such as soil and microbial biomass C, total and mineralizable soil N, and microbial N, but did not increase barley yield compared to continuous grain cropping.