Grazing Intensity Research On Coteau Rangelands


Introduction

Five grazing treatments, or intensities of grazing, are included in the study: no grazing, light, moderate, heavy and extremely heavy. Light is defined as that grazing intensity which leaves 65% of the forage produced in an "average" year at the end of the grazing season. The moderate grazing treatment is stocked to leave 50%, the heavy treatment 35% and the extreme treatment 20% of the forage produced in an average year. A certain amount of trial and error is required in adjusting stocking densities, grazing patterns and length of grazing season to achieve these grazing intensities. Each of these treatments is applied to three pastures so that differences due to grazing intensity can be separated from those due to natural variability of the pastures. Changes in the vegetation are monitored on plots located on silty and overflow range sites in each pasture. These sites are used because they are the most common in the Coteau region. Pastures with no grazing are simulated by fencing out areas on three silty range sites and three overflow range sites located within the grazed pastures.

Grazing begins each year around mid-May. Table 1 gives the stocking history of the study. To keep the same level of stress on the plants each year, grazing will continue until half of the amount of forage produced in an average year remains on the pastures grazed at the moderate rate. It will take several more years to determine the average productivity of these pastures.

Table 1. Stocking history of the grazing intensity trial.
Year Class of Animal Date
Stocked
Date
Removed
Length of
Season (days)
1989 Steers May 22 August 22 92
1990 Bred Heifers May 30 November 27 181
1991 Bred Heifers May 29 September 25 119
1992 Bred Heifers June 1 August 25 85
1993 Bred Heifers May 29 September 26 120
1994 Open Heifers & Steers May 17 November 10 177
1995 Open Heifers May 18 October 30 165
1996 Open Heifers May 20 September 23 126
1997 Open Heifers May 27 November 5
(August 27, extreme)1
162
(92, extreme)
1998 Open Heifers May 16 October 28 165
1999 Open Heifers May 27 November 4 161
1Livestock were removed early on the extreme treatment due to a lack of forage.

Table 2 gives peak total forage production for 1989 through 1999 along with the precipitation for the year. Average production for 1989 to 1999 was 3,768 lbs/acre on overflow range sites and 2,741 lbs/acre on silty range sites. Therefore, an average of 1,884 lbs/acre should remain on overflow sites and 1,371 lbs/acre on silty sites at the end of the grazing season on pastures stocked at the moderate stocking density.

Table 2. Total crop year precipitation (October 1 to September 30) and peak total above ground biomass production on overflow and silty range sites on the grazing intensity study from 1989 to 1999.
Year Precipitation
(in)
Above Ground Biomass Lbs/Acre
Overflow Silty
1989 18.40 3,863 2,089
1990 16.10 3,847 2,962
1991 12.89 3,142 2,629
1992 15.25 2,758 2,065
1993 26.59 3,999 3,446
1994 16.86 4,201 2,803
1995 22.60 4,773 3,134
1996 20.55 3,837 2,645
1997 18.63 3,351 2,376
1998 18.91 3,334 2,855
1999 26.91 4,338 3,152
11-Year Average 19.43 3,768 2,741

Figure 1 shows the forage remaining at the end of the grazing season for each treatment in each year of the study. Reference lines indicate the amount of forage we would like to see remaining for each grazing treatment. This shows the progress being made in adjusting stocking rates to achieve the desired use levels at the end of the grazing season.

Above ground biomass remaining (lbs/acre) on each treatment at the end of the grazing season from 1989 to 1999.
  Treatment
Year Light Moderate Heavy Extreme
1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

Ideal Remaining

2,078

2,634

2,385

1,915

2,924

2,017

2,772

2,552

2,550

2,674

2,269

2,107

2,074

2,383

1,494

1,353

2,256

1,728

1,906

1,975

1,711

1,848

2,108

1,690

2,035

2,023

833

574

1,290

1,393

1,583

1,064

689

686

806

980

1,701

1,985

641

406

608

901

504

513

560

522

609

518

 



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