Nutrient loss from agricultural practices can impair water quality.
Agricultural runoff is a significant source of total phosphorus and nitrate-nitrogen losses into Illinois waterbodies and the Mississippi River. Total phosphorus losses are typically due to soil erosion into surface waters, while nitrate-nitrogen losses commonly occur when nutrients are carried in tile drainage water. Both routes affect the quality of surface and groundwater.
Nutrients from Illinois end up in the Mississippi River.
The following statistics summarize baseline measurement information from 1980 to 1996. More information can be found in the 2015 Illinois Nutrient Loss Reduction Strategy Science Assessment Findings. A Hydrologic Unit Code, HUC, is a nationwide numbering system the U.S. Geological Survey uses to categorize watersheds at various scales. A HUC 8 is an eight-digit number that uniquely defines a watershed. Illinois is home to 50 HUC 8 watersheds.
Nitrate-Nitrogen Losses
- 80% of nitrate-nitrogen losses are accounted for by agricultural sources.
- The average nitrate-nitrogen loss was estimated at 10 lbs per acre yearly and ranges from 0.7 lbs to 42 lbs per acre yearly.
- 27 of Illinois' HUC 8 watersheds show losses greater than 10 lbs per acre yearly.
- The highest nitrate-nitrogen losses were found in the tile-drained region in the northern two-thirds of the state.
Phosphorus losses
- 48% of total phosphorus losses are attributable to non-point sources, which are largely from agricultural sources.*
- The average total phosphorus loss was estimated at 1.4 lbs per acre yearly and ranged from 0.42 to 9.74 lbs per acre yearly across HUC 8 watersheds.
- The highest total phosphorus losses were typically found in southern Illinois.
*Note, the percentages attributed to each sector are based on the initial nutrient science assessment by the Illinois EPA, IDOA, and University of Illinois Extension (2015, Illinois Nutrient Loss Reduction Strategy). As the strategy evolves and new research emerges, adjustments to these attributions may be required, potentially incorporating additional categories for nonpoint sources.
Keep nutrients in the field where they belong.
The Illinois Nutrient Loss Reduction Strategy recommends a variety of agricultural conservation practices to reduce nutrient losses that have been scientifically assessed. The following practices have been rigorously tested for their proven effectiveness in retaining nutrients on the farm. The list is not all-inclusive. Soil characteristics, landscape position, hydrology, existing management practices, and other factors all affect the suitability of a practice for a field.
These practices fall into three categories: in-field strategies, edge-of-field techniques, and land-use changes.
In-Field Practices
| Practice | N reduction | P reduction | Annual cost per acre |
|---|---|---|---|
| Cover Crops (grassed-based) | 30% | 30% - 50% based on tillage choices | $29 |
| Maximum Return to Nitrogen Calculator | 10% | 0% | -$8 |
| Soil Test Phosphorus | 0% | 7% | -$8 |
| Conservation Tillage | 0% | 30% - 70% based on tillage choices |
-$17 to $11 based on tillage choices |
| Nitrogen Inhibitor | 10% | 0% | $7 |
| 50% Fall Nitrogen / 50% Spring preplant Nitrogen | 7.5% - 10% | 0% | $17 |
| 40% Fall Nitrogen / 10% Preplant / 50% Sidedress | 15% - 20% | 0% | $17 |
| Spring only Nitrogen | 15% - 20% | 0% | $18 |
| Terraces | 0% | 40% | $40 |
| Water and sediment control basins | 0% | 60% | $64 |
Edge-of-Field Practices
| Practice | N reduction | P reduction | Annual cost per acre |
|---|---|---|---|
| Bioreactor | 25% | 0% | $17 |
| Wetland | 50% | 0% | $61 |
| Saturated Buffers | 40% | 0% | $10 |
| Buffers (non-tiled) | 90% | 25% - 50% | $294 |
Land Use Change
| Practice | N reduction | P reduction | Annual cost per acre |
|---|---|---|---|
| Perennial / Energy Crops | 90% | 50% - 90% based on tile drainage / tillage type |
$86 |
Sources: 2015 Illinois Nutrient Loss Reduction Strategy; 2021 Illinois NLRS Biennial Report; U.S. EPA, The effects: Dead zones and harmful algal blooms; National Centers for Coastal Ocean Science, Congressional interest in harmful algae and dead zone bill prompts hearing; U.S. EPA, The Effects: Dead Zones and Harmful Algal Blooms; USDA, Impacts and repercussions of price increases on the global fertilizer market
Choosing farming practices that protect water quality.
The NLRS Agricultural Water Quality Science Team reviews proposals to add new conservation practice recommendations or to adjust the performance values of a practice. The team evaluates proposals and shares its recommendations, including performance values and cost estimates for recommended practices, with the Illinois NLRS Policy Working Group. Sometimes, the team decides that a practices needs more research before it can be added as a recommended NLRS practice.
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