Soil compaction under grazing of annual and perennial forages

This study investigated the impact of heavy, medium and light grazing of me adow bromegrass an triticale on soil bulk density, relative compaction and penetration resistance. The study was conducted at Lacombe, Alberta, on a O rthic Black Chernozem of loam to silt loam texture. Sampling was conducted in fall 1995, spring 1996, fall 1996 and spring 1997. Core samples to a 15- cm depth were collected for measurement of bulk density and moisture conten t. Penetration resistance to 15 cm was measured with a hand-pushed cone pen etrometer. The standard Proctor test was used to determine maximum bulk den sity. Relative compaction was the ratio of actual bulk density to the Proct or maximum bulk density expressed as a percentage. Surface (0-2.5 cm) bulk density and penetration resistance were significantly greater under heavily grazed than under medium and lightly grazed meadow bromegrass only for fal l 1995. Differences in bulk density, relative compaction and penetration re sistance for different grazing intensities in spring and fall 1996 and spri ng 1997 were either small or not significant. Generally, bulk density decre ased over winter in the top 2.5 cm, was not consistent in the 5- to 10-cm d epth interval and did not change in the 10- to 15-cm interval. Except in fa ll 1995, the relative compaction values for all grazing intensities and for age species were less than 90%, a value considered critical for plant growt h. Generally, within each grazing level, there were minimal differences in bulk density, relative compaction and penetration resistance under tritical e compared to those under meadow bromegrass.