Environmental changes lead to more low-quality forage

Cattle Market & Farm Reports, Editorials
Jan 24, 2005
by WLJ
Producers are well aware of the environmental changes that have evolved over the past decade or two. But, are producers prepared for future changes to the environment?
Agriculture Research Service (ARS) scientists want producers to be aware that the ongoing drought may not be the only difficultly they need to account for in their production operation. These scientists are saying that elevated concentrations of carbon dioxide in the atmosphere may reduce forage quality, leading to reduced weight gain or more costly gain for livestock.
Plant physiologist Jack Morgan at Colorado State University lead the study with ARS colleagues and cooperators. Morgan explained that researchers have noticed a steady rise in the concentration of carbon dioxide (CO2) during the last 150 years. Scientists expect the level of CO2 to keep rising mainly because of fossil-fuel burning, forest clearing and industrial manufacturing. If the theory of the intergovernmental panel on climate change holds true, atmospheric CO2 concentrations will double from today’s levels by the end of the 21st Century. In short, this will mean that the increased level of CO2 in the air will cause forage quality to drastically decline and leave producers with lesser quality feedstuffs.
To test the possible effects, Morgan said researchers constructed six large chambers and installed them over native shortgrass prairie vegetation at the USDA ARS Central Plains Experimental Range in northeastern Colorado. Each chamber contained more than 25 different plant species, but was dominated by three perennial native grass species. This plant community was characteristic of vegetation grown in semi-arid grassland for thousands of years.
The study was conducted over five years. During this time, half of the chambers were maintained at present atmospheric conditions of carbon dioxide. The other half of the chambers were enriched in CO2 to double the present carbon dioxide concentration from today’s concentration of about 360 parts per millions of CO2 to 720 parts per million-the expected level at the end of this century.
Morgan said researchers found that increasing CO2 also increased plant growth. On average, more than a 40 percent increase in plant production occurred under doubled CO2 conditions. However, while there were more plants, forage quality declined in all three of the dominant grasses. The researchers primarily contributed the drop in quality to a decline in nitrogen concentration, or crude protein, in the plant shoots.
“One might think that even with a decline in forage quality, this may not sound so bad since production increases so much,” said Morgan. “However, livestock performance can be limited by forage quality, and a decline in quality on native grasslands, where soil nutrients are not nearly as abundant as they can be in improved pastures, can have a significant negative impact on animal performance.”
Many of the ARS colleagues share the opinion with Morgan that the decline in forage quality due to rising atmospheric CO2 may be one of the more important issues of global change facing ranchers. Of course, these researchers don’t want producers to be alarmed and think this will happen over night. Instead, scientists agreed that this will be a gradual change that will unfold over decades.
“This study suggests that over the long haul, rising CO2 may significantly decrease forage quality across our native rangelands,” said Morgan. “The significance of this to cow/calf producers is that rising atmospheric CO2 may slowly be degrading the quality of native grasses their animals rely on.”
Because this is such a critical matter for producers, the Rangeland Resources Research Unit has decided to continue its research. The next step Morgan says is trying to understand how rising levels of atmospheric CO2 affect the nitrogen cycle in nature. In conjunction with that study, one of the objectives is to determine whether there might be economical means to solve the problem of declining forage quality in native rangelands.
The Fort Collins research station is also conducting research on grazing practices that may result in trapping more CO2 in rangeland soils. One theory is that producers could be able to inter-seed legumes into rangelands, which may improve the forage quality and also lead to more soil carbon storage.
When asked what producers can do about the problem now, Morgan said there isn’t really a whole lot they can do, other than watch for research data which will suggest a solution.
“At this point, I think this is an issue that producers and researchers ought to know about, just like we need to understand the long-term consequences of air pollution on human health,” said Morgan. “We are likely many years from solving this problem, but we wouldn’t be able to do much unless we know there is a problem in the first place.”
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