A recent University of Wisconsin-Madison study found that most Wisconsin farmers over-apply nitrogen and phosphorus to their corn fields although applying the correct amount would save them money and reduce harm to surface and ground water.
The study”s author believes those results point to the need to change the way we develop agricultural best management practices (BMPs) — such as nutrient crediting — which are meant to protect the environment.
Currently, government programs encourage farmers to credit on-farm sources of nitrogen and phosphorous. But nutrient crediting hasn”t been implemented successfully because it fails to consider the social and behavioral aspects of farming, according to Robin Shepard, who develops conservation education programs and studies their effectiveness. Shepard published his findings in the Journal of Soil and Water Conservation.
“The typical approach has been to develop a technical fix, a method farmers can use to solve a problem, and then employ financial incentives or regulatory threats to induce farmers to change the way they operate,” he says. “Instead, we need to understand why farmers engage in farming methods that harm the environment and develop best management practices from that knowledge. Meaningful involvement by farmers at the beginning of a project could lead to the design of true best management practices.”
For more than a decade as a member of the UW-Extension and College of Agricultural and Life Sciences, Shepard has been studying how farmers respond to new agricultural practices meant to protect the environment — particularly nutrient crediting.
A commonly promoted BMP in Wisconsin, nutrient crediting ideally protects water quality by reducing the amount of phosphorus that is available to run off fields and into streams and lakes. Crediting can also reduce excess nitrogen that can leach into ground water. By crediting nitrogen and phosphorus from on-farm sources, farmers can reduce their need for commercial fertilizers as well as decreasing the overall application of excess nutrients to farm fields.
To implement nutrient crediting, farmers must calculate the nitrogen and phosphorus applied to each field from on-farm sources. Those sources include nitrogen-fixing crops grown the previous season and manure spread on farm fields. Then the farmers “credit” those on-farm nutrient sources by applying commercial fertilizer to those fields at reduced rates.
Between 1990 and 1998, Shepard collected data about nutrient crediting on more than 1,900 Wisconsin farms from 20 locations in the state. Each farm had at least 40 acres of land and 15 head of cattle. The study found that two out of three farmers apply excess nitrogen and four out of five apply excess phosphorus to their corn. Few of the farmers used nutrient crediting practices appropriately.
Shepard says these results were particularly discouraging because he interviewed farmers from locations with known water quality problems and active programs targeting water protection.
The results highlight two key findings, according to Shepard.
First, the people responsible for implementing water protection programs must do more than try to increase the number of farmers using best management practices. “Simply promoting BMPs will not guarantee that we are protecting or improving water quality,” he says.
And second, a small percentage of farmers present a disproportionate threat to water quality. “We really don”t know much about this minority of farmers,” he says. “As program budgets shrink and accountability grows, protection efforts should focus on the farmers needing assistance the most.”
“On average, farmers in the study applied an excess of 38 pounds of nitrogen per acre and 74 pounds of phosphorus per acre,” Shepard says. “But we also found that a relatively small percentage of the farmers contributed disproportionately to the excess nutrient applications. For example, most of the farmers surveyed would, on average, apply about 160 pounds of nitrogen per acre. However, 14 percent of the farmers applied more than 318 pounds per acre and seven percent exceeded 400 pounds per acre. The situation with phosphorus is similar.”
The study also shows that most of the excess nutrients on cornfields come from manure spread there. Shepard sees several possible reasons for the failure to credit the manure properly.
Farmers face engineering limitations. The box-style manure spreader widely used across the state is designed to get rid of a waste rather than manage a valuable nutrient source.
Most water protection programs have emphasized building expensive manure storage structures while failing to emphasize the crediting behaviors needed to manage the manure stored in those structures.
Fertilizer dealers make recommendations while underestimating manure applications because of uncertainties about the type, amount and evenness of its distribution.
Although farmers recognize manure”s value as a soil amendment, they find it difficult to act on this knowledge because of their farm work schedules.
“We”ve made a great deal of progress in understanding agriculture”s impact on water quality,” Shepard says. “What remains are the complex and difficult challenges of changing agronomic behavior, farmer by farmer, one at a time.”
Shepard”s research was supported by state funding to the UW-Madison College of Agricultural and Life Sciences and UW-Extension, and grants from several state and federal agencies, including the Wisconsin Department of Natural Resources, the USDA Natural Resources Conservation Service, and the USDA Cooperative State Research, Education and Extension Service.