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
|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
|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.|
|Above Ground Biomass Lbs/Acre|
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.|