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.