The concept of deferred and rotation grazing was developed on an early hypothesis that considered the only process to improve degraded native rangeland was to reseed the land by mechanical methods or by letting the grass plants produce seeds and trample the seeds into the ground with livestock.
Recruitment of new grass plants developed from seedlings is negligible in grassland ecosystems. The frequency of true seedlings is extremely low in functioning grasslands.
Vegetative tiller growth is the dominant form of reproduction in semiarid and mesic grasslands not sexual reproduction and the development of seedlings making the deferred-rotation grazing practices obsolete.
The deferred-rotation grazing system was developed by Arthur Sampson (1913, 1914) from research conducted in the Blue Mountains of Oregon. The second version was a three-pasture system with grazing separated into spring, summer, and fall. The intended purpose of deferment was to increase seed production.
Sampson and Jardine knew that grass seeds that drop from a grass head and germinate have an extremely low survival rate. Late season trampling by cattle seemed to be the only way to get the dropped seeds too the soil.
The grasses of Oregon produce vegetation tillers, but because of the lack of rainfall during summer, they are usually inhibited by low soil water to grow during that growing season. The grazing activated vegetative secondary tillers appear the next spring, a month or more ahead of normal lead tiller development.
Sampson did not recognize these early spring tillers as last grazing season stimulated vegetative tillers. At that time, pasture scientists, were trained as agronomists, knew that some grasses produced vegetative tillers. However, the importance of vegetative tillers was dismissed.
Grass seed production and seedling establishment was far more important for the improvement of pasture forage production according to the agronomic based scientific concepts of the time.
A grazing investigation was conducted by J.T. Sarvis at the Mandan, North Dakota, Northern Great Plains Field Station to study the three-pasture deferred and rotation grazing treatment that was developed by Sampson and adapted and put into practice by the US. Forest Service in order to determine the performance of its direct application in the northern Great Plains. The grazing investigations were conducted for 23 years from 1918 to 1940.
Seventy acres were divided into three equal pastures to be grazed during spring, summer, and fall periods. A comparable control treatment was seventy acres in one pasture grazed season-long. The intended grazing season was 150 days from mid-May to mid-October. The research animals were two years old grade steers of standard beef breeds of Angus, Herefords, and Shorthorns with the mean initial weight of 750 pounds.
Sarvis developed grazing guidelines that required that 15% to 25% of the annual forage production to remain standing at the end of the grazing season. However, in practice the reported mean forage use on the deferred pastures was 92% removed and the mean forage use on the standard season-long pasture was 77% removed.
When the steers on the grazing treatments appeared to have lost weight, they were weighed at five- or ten-day intervals and when the weight loss was documented the steers on the season-long treatment were removed from the study pasture and moved to the reserve pasture.
When forage on the fall pasture of the deferred treatment became short and inferior and the steers began to lose weight, the steers were moved to the spring pasture that had new secondary growth. This new secondary growth was not recognized as vegetative reproduction of tillers from axillary buds.
During the first two years, ten steers grazed the deferred and season-long treatments at the same stocking rate. However, the steers on the deferred treatment gained a mean of only 260 pounds which was much less weight than the steers on the season-long treatment that gained a mean of 309 pounds.
After 17 years, the mean weight gain per head on the deferred treatment reached 266.1 pounds and the gain per head on the season-long treatment dropped to 308.3 pounds.
The lower weight gain for the steers on the deferred treatment were explained by Sarvis, “The deferred and rotation pastures show either light gains or losses for the month of October and somewhat reduced gains during September. The lower gains during the latter part of the season do not necessarily condemn fall grazing. This is the time when cattle put on the “finish” so often referred to by stockmen, which is apparently a hardening process brought about through a reduction in the quantity of water that they drink, as well as a change in the condition of their flesh. In the fall they will “shrink” less than they would earlier in the season. The cooler weather of autumn always causes shrinkage of the cattle, which is recorded as a loss in weight.”
Sarvis failed to explain why the steers on the season-long treatment did not experience the same degree of “finish” as the steers on the deferred pasture.
Sarvis explained the purpose of the deferment, “This deferred and rotation grazing system is designed to allow each division of the pasture to mature a crop of seeds before it is harvested by the cattle in the fall of each year. Grazing on each division is deferred and rotated. The seeds of the grasses which are scattered on the ground are aided in their planting by trampling of the cattle.
Sarvis (1941 p.80) concluded, “So far as it has been possible to determine, there has been no significant benefit from reseeding of the grasses under this deferred and rotation grazing system during this experiment after 23 years.”
Sampson knew that cattle produced very low weight gains on the deferred pastures, he knew that some grasses reproduced vegetatively, and he did not have documentation that the production of seeds resulted in greater numbers of seedlings.
The US Forest Service knew that cattle produced very low weight gains on the deferred pastures, and they did not have documentation that the production of seeds resulted in greater numbers of seedlings.
Sarvis knew that two-year-old steers produced very low weight gains on the deferred pastures, he documented that the number of seedlings did not increase on the deferred treatment, and he documented a large reduction in grass density. Sarvis did not consider the high forage use at 85% to 75% to be a factor in grass density reduction.
Despite the lack of supporting scientific data, these pasture agronomists still continued to promote the use of the deferred-rotation grazing practice to livestock producers west of the Mississippi River.
An early hypothesis that required reseeding to restore degraded grasslands was used to develop the deferred-rotation grazing practice. However, the concept that recruitment of new plants on grassland ecosystems comes from seedlings was not proven. New grass plants develop from vegetative secondary tillers. Because of the early pasture scientists dismissed the importance of vegetative tillers, the deferred grazing practices caused further ecosystem degradation and poor livestock weight gains. The deferred practice does not increase grass seedling establishment.
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