Over-Applying Farm Chemicals Can Lead to Water Quality Issues
The Gulf of Mexico's "Dead Zone" is largely attributed to agricultural runoff from the Midwest. Agriculture has been similarly targeted closer to home, where amounts of nitrogen in Iowa's drinking water supplies have increased dramatically throughout the past century. For example, in a 2000 U.S. Geological Survey study, average annual nitrate concentrations in the Des Moines and Cedar Rivers have increased nearly seven times over the last 100 years, from about 0.6 milligrams per liter to as much as 4.6 mg/l. And data provided by Des Moines Water Works dating back to the 1930s shows nitrate levels in the Raccoon River stayed consistently below 1 mg/l until the mid 1960s. Since then, nitrate levels have increased to as high as 10.2 mg/l in 2002. Over the last 20 years, average nitrate levels in the Raccoon River average 7.3 mg/l.
What Can Be Done
- Reduce inputs. The best way to prevent nitrates and other chemicals from leaving crop fields, either through runoff or leaching into groundwater, is to simply reduce the amount of fertilizer and pesticides that are applied.
- Improve soil health. Healthy soils have deeper topsoil layers which are high in organic matter. This organic matter layer allows soils to hold water and nutrients like a sponge until plants need them. Ways to improve soil health include reducing or eliminate soil disturbing activities, such as tillage, and adding diversity to a crop rotation, with practices like cover crops.
- Implement a Drainage Water Management (DWM) system. DWM systems allow farmers to manage drainage tile water levels with a water control structure, much like those used to control wetland water levels. Water level structures are simply retrofit to an existing tile system.
4R Nutrient Stewardship
SMART Nutrient Management
NRCS works with farmers to develop nutrient management plans that optimize plant yields while reducing the amount of nutrients lost to the environment, where they can impact greenhouse gas emissions and air and water quality.
SMART Nutrient Management includes the 4Rs of nutrient stewardship – the right Source, right Method, right Rate, and right Timing – and emphasizes smart activities to reduce nutrient loss by Assessment of comprehensive, site-specific conditions.
A SMART Nutrient Management Plan considers all conditions on the farm and how they influence one another. It is tailored to the unique farm location, soil, climate, crops grown, management conditions, and other site-specific factors.
Iowa Phosphorus Index - Technical Note 25
Iowa NRCS and Iowa State University has developed an Iowa Phosphorus Index (PI). The Iowa PI is an assessment tool for the purpose of evaluating the potential of off-site phosphorus movement. This Iowa PI is to be used when a NMP is being developed based on the 590 Standard and one of the following conditions exist: 1. When manure is applied. 2. Soil loss is above the tolerable level (T). 3. The planning area is within an identified nutrient impaired watershed. 4. The soil test phosphorus levels are above optimum.