While farmers have reduced nutrient and sediment losses from croplands in the Bay watershed, about 80 percent of those lands continue to have a "high" or "moderate" need for further actions to protect water quality, according to a new report from the U.S. Department of Agriculture.
The report provides a complex look at crop farming in the watershed. On one hand, it suggests that actions taken by farmers have significantly reduced sediment, nitrogen and phosphorus pollution. On the other, it shows that significant hurdles remain. For instance, acres that receive manure for fertilizer have more than twice the nutrient loss than those that receive chemical fertilizer.
And while the study found farmers were taking more conservation actions than previously estimated, it also found that some of those actions - when taken in isolation - have the potential to exacerbate some water quality problems.
"This study confirms that farmers are reducing sediment and nutrient losses from their fields," said Dave White, chief of USDA's Natural Resource Conservation Service. "Our voluntary, incentives-based conservation approach is delivering significant and proven results. This study will help us improve our conservation practices in the Chesapeake Bay area."
The Bay watershed has about 84,000 farms that cover nearly 30 percent of the basin. The report, from the USDA's Conservation Effects Assessment Project (CEAP), examined only cropped acreages, which occupy about 10 percent of the watershed. Cropped lands tend to have greater runoff than other farm land, such as pasture or hayland, contributing 31 percent of the nitrogen and 28 percent of the phosphorus and 21.5 percent of the sediment that reaches streams in the watershed, according to the report.
The report found that most of the 4.3 million acres of cultivated land have received some type of conservation efforts - sometimes more than reported to state or federal agencies. For instance, it said reduced tillage practices were used on about 88 percent of cropland, nearly twice the official estimates. Still, most farmers have fallen short of comprehensively managing the sediment and nutrient issues on all of their fields.
In some cases, that piecemeal approach to conservation can worsen some types of pollution. For instance, the report said that while conservation practices such as terraces or no-till farming can substantially reduce erosion, they can also increase the amount of nitrogen that reaches groundwater unless nutrient applications are carefully managed. Once it reaches groundwater, that nitrogen can no longer be removed by plants before it reaches local streams. Overall, the report estimated that nitrogen losses had increased on 17 percent of the fields where erosion control practices were installed, although most increases were small.
"If you focus on one concern, you will miss the boat," said Doug Lawrence, NRCS deputy chief for soil survey and resource assessment. "If you don't have nutrient management, you will probably add nitrogen to the subsurface flow pathways. One of the major findings is that the subsurface component needs to be addressed."
The report was based on a variety of USDA data collected from 2003 and 2006, along with detailed surveys of more than 771 farmers in the Bay watershed. That information was used in conjunction with computer models to estimate the effect of conservation actions taken by farmers through 2006, and to identify potential management actions for the future.
The study found that conservation efforts by farmers over the decades have cut sediment losses from fields by 55 percent, nitrogen losses in surface runoff by 42 percent, nitrogen losses in subsurface flows by 31 percent and phosphorus losses by about 40 percent.
The report also emphasized the need to target farms where conservation efforts are the lowest and soils most vulnerable to sediment and nutrient losses for future efforts. It noted that runoff and leaching rates vary widely because of factors such as slope and soil type, and found that while 59 percent of cropped acres lose less than 40 pounds of nitrogen a year, 10 percent lose more than 100 pounds of nitrogen annually.
The report said 19 percent, or 810,000 acres, of cropland had a "high" level of need for additional conservation efforts, and 61 percent, or 2.6 million acres, had a "moderate" level of need for additional action.
Targeting those areas for a comprehensive suite of nutrient and sediment control practices would cut sediment losses by an additional 87 percent, nitrogen losses in surface flows by 66 percent, nitrogen in subsurface flows by 53 percent, and phosphorus by 57 percent.
Kelly Shenk, agricultural policy coordinator with the EPA's Chesapeake Bay Program Office, said the report's emphasis on targeting meshes well with priorities established by states in their Watershed Implementation Plans to achieve Bay nutrient reduction goals.
"It confirms what we know - that conservation works - but that we need to do more," Shenk said. "The CEAP study tracks very well with actions state have committed to take in the watershed implementation plans."
The single greatest need in the watershed, the CEAP study said, was "complete and consistent use of nutrient management." That includes applying nutrients at the appropriate rate based on soil conditions and plant needs, and applying them in the appropriate form at the appropriate time and with the appropriate methods.
While many farmers met some of those objectives some of the time, the report said only 13 percent of the acres met all criteria for nitrogen, and 17 percent did so for phosphorus. Just 6 percent of cropped acres met all nutrient management criteria for both nitrogen and phosphorus.
The situation was worse on the 38 percent of cropland that relies on manure for fertilizer. That's not surprising, as manure is typically more difficult to handle and apply, and the nitrogen to phosphorus ratios in manure are typically different from those needed by crops.
That translates into water quality problems. On average, the report found that acres receiving manure lost an average of 75 pounds of nitrogen per year. Meanwhile, lands that didn't receive manure lost an average of 35 pounds.
The situation was worse for phosphorus: Acres getting manure lost an average of 6.2 pounds per acre, compared with 2.3 pounds per acre for those that did not.
The notion that farm conservation programs have resulted in nutrient reductions as great as those cited in the CEAP study was challenged by scientists who monitor water quality in the region.
"Those reductions in losses don't square with the data," said Russ Brinsfield, executive director of the University of Maryland's Harry Hughes Center for Agro-Ecology.
"You would expect that if we had had those type of reductions, we would see some signal," Brinsfield said. At best, he said, "the rates of increase (of nutrient pollution) may be decreasing."
A U.S. Geological Survey report released last fall showed that phosphorus trends in most Bay tributaries have increased since 2000.
Lawrence suggested that other factors may contribute to the lack of improvement recorded by in monitoring. For example, he said, a backlog of phosphorus could be stored in stream banks and slowly be released as moving water eats into those banks.
"I think in many cases, everyone would agree that there will be some significant lags in seeing results in the Bay," he said.
The report said that controlling nutrient and sediment pollution from croplands is especially difficult in the Chesapeake watershed. Compared with the Upper Mississippi basin - the site of the only previous CEAP study - the Bay watershed gets on average 8 additional inches of rain per year, has proportionally more land with steeper slopes, more land that is prone to runoff or leaching into groundwater, and more land that relies on manure as fertilizer.
Taken as a whole, cropland in the Bay watershed loses 10-20 percent more nitrogen, phosphorus and sediment per acre than cropland in the Upper Mississippi.
The USDA is now conducting a follow-up study that could show stepped-up efforts on farms in recent years as a result of sharply increased Farm Bill funding for conservation efforts in the Bay watershed. On the other hand, USDA figures have also showed an intensification of crop planting in the region since 2006, which would require more conservation efforts to offset.
That report is expected next year.
Farming the Chesapeake Watershed by Numbers
The 2007 value of agricultural sales was $9.5 billion: 24 percent from crops, 76 percent from livestock.
There are 84,000 farms in the Bay watershed.
Of these farms, 51 percent primarily raise crops; 42 percent are primarily livestock operations; and 7 percent produce a mix of livestock and crops.
Of these farms, 74 percent are small operations with less than $50,000 in total farm sales.
Of these farms, 7 percent had total farm sales greater than $500,000.
Forty-three percent of these farms are smaller than 50 acres.
Corn and soybeans are the principal crops grown.
Livestock operations in the region produced 10 percent of all of the poultry and egg sales in the United States in 2007, exceeding $3.7 billion in value.
Sales of dairy products ranked second in the region at $2.2 billion, representing 7 percent of the U.S. total.
Populations of pastured cattle, horses and ponies represent about a third of the total livestock population in the region measured in animal units. (An animal unit is about 1,000 pounds.)