The naive homesteaders, had no technological assistance from the government on how to properly manage Northern Plains grasslands; they implemented eastern grazing practices with stocking rates at greater than 60% heavier than the biological carrying capacity for grasslands west of the 20 inch rainfall line. As a result, the grassland resources deteriorated and herbage biomass production decreased with disproportional reduction of mid cool season grass species, and leaving a predominance of short warm season grass species (Whitman et al. 1943).
Branson (1953) determined that grass species with long shoots that elevated the apical meristem above grazing height decreased at greater rates than grass species with short shoots that kept the apical meristem below grazing height in pastures that are repeatedly grazed with heavy stocking rates.
Crider (1955) determined biologically that stocking rates should only remove about 50% of the herbage biomass because grass tillers that had more than 50% of the aboveground leaf and stem material removed would develop reduced root growth, root respiration, and root nutrient absorption causing grass plant deterioration. About half of the expendable leaf material is removed as senescent leaves that are broken from the plant and fall to the ground as litter, or removed as leaf material by wildlife, grasshoppers, and other small animals. About half of the expendable leaf material, or 25% of the aboveground grass biomass can be consumed by grazing graminivores.
Crider’s monumental research to determine the biological threshold level of herbage weight removal from grass plants was desperately needed to set proper stocking rates. Crider’s work was some of the first grassland research to actually study the belowground components in order to determine how to manage the aboveground components. He also showed that biological, physiological, and ecological sciences could be effectively applied to develop proper grassland management practices.
Coyne et al. (1995) determined that grass plants produce double the quantity of aboveground leaf and stem biomass than is needed for photosynthesis and normal growth and development.
Scientists have also determined that Crider’s 50% plant material removal does not work at all phenological growth stages of grass. Briske and Richards (1995) determined that stored root carbohydrates were not remobilized to support replacement shoot growth following partial defoliation by grazing livestock. The carbohydrates needed for replacement shoot growth must come from currently fixed carbon during photosynthesis in remaining and rejuvenated leaf area from existing shoot material.
A problem develops when 50% of the grass herbage is removed during lead tiller vegetative growth stages between the 3.5 new leaf stage and the flower (anthesis) stage, the remaining 50% leaf area cannot supply adequate quantities of currently fixed carbon causing grass tiller density to be reduced 13% per year.
However, when only 25% of the grass herbage is removed during lead tiller vegetative growth stages, the quantity of young leaf material removed also removes sufficient quantities of the growth-inhibiting hormone, auxin, which then permitted the synthesis or utilization of the growth hormone, cytokinin, to activate the asexual processes of vegetative tiller production in several axillary buds. The remaining 75% leaf weight had sufficient leaf area to fix carbon at adequate quantities for growth and development of these vegetative tillers at a level that beneficially increased tiller density 25% per year. After the flower stage, late July, 50% of the grass herbage can be removed as Crider determined.
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