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 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.
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 |