Impacts of forage grazing and cultivation on near-surface relative compaction

The study was conducted at the Lacombe Research Station, Alberta, on an Ort hic Black Chernozem of loam to silt loam texture to investigate grazing imp acts and cultivation on nearsurface soil compaction. Four forages, smooth b romegrass (Bromus inermis Leyss 'Carlton'), meadow bromegrass (Bromus ripar ius Rhem 'Paddock'), a mixture of triticale (X Triticosecale Wittmack 'Pika ') and barley (Hordeum vulgare L. AC Lacombe), and triticale were used for the study. Each forage species was subjected to heavy, medium acid light in tensity grazing. Measurements of bulk density and volumetric moisture conte nt for the 0- to 10-cm depth interval were conducted using a surface moistu re-density probe between spring 1994 and fall 1996. Relative compaction was calculated as the actual bulk density expressed as a percentage of the Pro ctor maximum density. Relative compaction values for all treatments and tha t for the benchmark were less than 90%, which is considered critical for li miting plant growth. Cultivation reduced bulk density under annual forages by only 3% and lowered it under heavy grazed annual treatments most. Regres sion analysis conducted on the dependence of bulk density to cumulative cow -days indicated a curvilinear relationship. Bulk density increased more rap idly with increasing cumulative cow-days for annuals compared to perennials . From a management perspective, adopting intensive rotational grazing syst ems for perennial and annual forages may not cause any serious surface comp action problems for soils in this area.