EFFECT OF INTEGRATED MANAGEMENT OF COUCH GRASS (ELYTRIGIA-REPENS) ON SOIL QUALITY AND CROP NUTRITION

The effects of suppressing couch grass (Elytrigia repens L.), through integrated management, on soil biological quality and N and P nutritio n of barley (Hordeum vulgare L.) were evaluated in a field experiment (1987-92) on a Dark Grey soil in Alberta, Canada. The management pract ices consisted of combinations of herbicide application, crop rotation s and tillage treatments. The 3-year crop sequences consisted of conti nuous barley, canola (Brassica rapa L.)-barley-barley, fallow-barley-b arley, and barley or canola undersown with red clover (Trifolium prate nse 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 m icrobial biomass with these treatments than with similar herbicide-tre ated crop rotations. Tillage-plus-herbicide treatments effectively sup pressed couch grass and enabled the barley crop to compete for soil N, however, both spring and autumn tillage were required for weed contro l. The fallow treatment impaired soil quality by reducing soil and mic robial C and N, but produced similar barley yields as continuous cropp ing with tillage-plus-chemical control. Red clover ploughed in for gre en manure enhanced soil quality indicators such as soil and microbial biomass C, total and mineralizable soil N, and microbial N, but did no t increase barley yield compared to continuous grain cropping.