Grazing and fertilizer, compost or manure application effects on a meadow bromegrass pasture on a thick black chernozem I. Productivity and sustainability

Short duration, intensive grazing management with high stocking rates may result in sufficient turn-over of nitrogen (N) to compensate for production-limiting soil-N deficiencies for grass pasture. In central Alberta a 0.5 ha block was seeded to ‘Fleet’ meadow bromegrass (Bromus riparius Rehmann) in August, 2002. Within this block, six fenced (9 x 30 m) treatments were established in three replicates. They were: 1. ungrazed–clip removal; 2. grazed – alone; 3 grazed– fertilizer; 4. grazed – fertilizer-compost; 5. grazed - hog manure; 6. grazed – alfalfa (Medicago sativa L.) -grass. Measurements were conducted over a 4-year period between 2003 and 2006 and grazing occurred at identical times as vegetative mass permitted. Biomass was harvested before and after grazing for calculation of dry matter (DM) yield and biomass consumed. Subsamples were used for determination of N concentration and in vitro digestibility. Mean herbage N-yield for grazed treatments was 131% of ungrazed and greatest for grazed-fertilizer and grazed-fertilizer plus compost. Grazed paddocks with no added N produced similar DM yield to those with added N. Estimated nitrogen fixation contributed an annual average of 82 kg ha-1 to herbage-N yield from the alfalfa-grass paddocks. Barley (Hordeum vulgare L.) silage grown after termination of the grazed pastures produced 72% more herbage DM from grazed paddocks than ungrazed, but no significant (P. < 0.05) differences occurred among amendments.