The earliest known South Asian civilizations flourished in the Indus Valley from 3000-1500 B.C. in what is now Pakistan and India. The Indus Valley Civilization covered a 600,000-square-mile territory and included well-planned, major cities boasting large public buildings and underground sewers.
Though the valley was sacked and pillaged by invaders around 1500 B.C., archaeologists agree that the real decline began several hundred years earlier. They also know the reason: saline soils. Salinity, or excess salt in the soil profile, is often called the "silent killer."
The decline of agricultural civilizations due to soil salinity has been repeated countless times throughout history. Now, salinity is taking its toll on agricultural regions in the state of Colorado.
The Arkansas River in southeastern Colorado is one of the most saline rivers of its size in the United States. Salinity levels increase from 300 parts-per-million near Pueblo to more than 4,000 parts-per-million at the Colorado-Kansas border.
The Arkansas Valley has lost thousands of acres of agricultural land to salinity. Salinity problems now are beginning to show up in the South Platte River Basin, especially in Weld County, which is one of Colorado's most productive agricultural areas.
Luis Garcia, Colorado State University associate professor of civil engineering and interim associate director of the Colorado Agricultural Experiment Station, is studying salinity in the Arkansas and South Platte river basins. Garcia is monitoring fields to determine where salt accumulates and how it impacts crops.
"The salinity problem is farther along in the Arkansas Valley, and the impacts are more acute with respect to agriculture," says Garcia. "By studying the Arkansas, we hope to get an understanding of what might happen in the South Platte and, more importantly, what solutions the industry can implement."
In some cases, Garcia says farmers might need to change irrigation methods, add drains to their land, or reduce seepage from canals. Other options include planting crops that are more salt tolerant or those that use less water.
"It's also important to figure out where the salt is coming from," says Garcia. If the salt is contributed by subsurface return flows from the irrigated fields, then better field management to reduce leaching will help.
"If the problem is created outside of a particular farm, an individual farmer might not have enough control to implement effective changes," Garcia explains. "It requires resources outside of individuals to look at this issue on a larger scale."
Colorado State University Cooperative Extension and the Natural Resources Conservation Service currently are working with farmers and local communities in a coordinated effort within the typically independent agricultural industry. Using Geographic Information Systems (GIS), salinity measurement devices, and groundwater monitoring wells, an accurate picture of the distribution of salinity in individual fields and over time can be produced for farmers.
Garcia and others are producing maps of saline fields showing groundwater and soil salinity levels as well as crop yield reductions that change with time, reflecting an accurate picture of salinity problems. This information can be used to change irrigation timing and amounts, as well as identify sources of saline waters that reduce productivity. For examples, see the Web site for the Arkansas project at http://www.ids.colostate.edu/projects/arkansas.
"Farmers along the lower South Platte River already are experiencing declining productivity of their fields due to increased salinity," says Garcia. "When the salinity levels were low, the problem was masked by other issues. Now that the problem is becoming more widespread, farmers are becoming more aware of the possible long-term implications. They also are realizing that solutions need to be long-term."
With those realizations, Colorado agriculture is learning the lessons of history the hard way; it's not easy trying to grapple with a problem that has beaten so many in the past. Garcia hopes his work will help guarantee a better chance for the future.