Forage Resource Management and Integration

Management for Sustainability (page 4 of 6)
In theory, the idea of "taking half and leaving half" is one of the most important principles of range management; however, in practice, it is one of the most difficult to accomplish. Because cattle are very selective in their diets, they tend to graze the most desirable plants or areas first. They are also more likely to graze new, tender regrowth from a previously bitten plant than they are more mature plants. You may be "taking half and leaving half" by grazing all of some plants and none of others or grazing out one area (spot grazing) while another isn't even used. The term used for this is vertical grazing. The result is overgrazing and undergrazing occurring in the same pasture. Weeds tend to become more prevalent in the overgrazed areas while brush becomes more prevalent in the undergrazed areas. This is often the case in pastures that are continuously grazed. At this point, many producers respond with chemical control of weeds and brush. This may provide temporary relief, but it does nothing to fix the problem of inefficient grazing management practices.

The principle of "taking half and leaving half" only applies to horizontal grazing which means taking half of "each plant" and leaving half of "each plant." The most efficient way I know to do this, using livestock, is through rotational grazing. To stop overgrazing, I think it is necessary to have a minimum of eight paddocks per herd. This will allow plants sufficient time to recover between grazing intervals so long as the forage is properly stocked. As you increase beyond eight paddocks, thus increasing stock density, uniformity of utilization will increase through even better harvest efficiency of forages.

The diagram below represents different phases of plant maturity and outlines proper grazing management practices:

Click to enlarge

As a plant matures throughout the growing season, lignin content increases, palatability decreases, protein decreases and total digestible nutrients decrease. In relation to plant maturity throughout the growing season, Phase I growth represents minimal forage quantity but excellent forage quality while plant growth is slow. Phase II growth represents sufficient forage quantity and quality with rapid plant growth. Phase III growth represents maximum forage quantity, but poor forage quality, while plant growth is again slow. To optimize the quantity and quality of harvestable nutrients, forages should be used and maintained in Phase II growth.

In relation to a plant's ability to regrow after grazing, a pasture should not be grazed too short, leaving so little leaf that growth must return to Phase I. If a plant does return to Phase I, it must develop a completely new "factory" to begin photosynthesis. Likewise, a pasture should not be left to grow so long that it reaches Phase III. If a plant reaches Plant III, shading and old growth begin to reduce photosynthesis. We should attempt to maintain a pasture in Phase II so plants will have the ability to regrow more rapidly. To do this, the periods between grazing must vary according to the rate of plant growth. When growth is fast, the rest periods should be shorter. When growth is slow, the rest periods should be longer.