Minnesota Watershed Nitrogen Reduction

Planning Tool

William LazarusDepartment of Applied Economics

University of MinnesotaDavid Mulla

Department of Soil, Water, and ClimateUniversity of Minnesota

David WallMinnesota Pollution Control Agency

Download paper at: z.umn.edu/nbmppaper

Reasons for Study

• Proposed MPCA standards for nitrate in surface waters – adoption are a couple years away. – “Impaired waters” status would trigger TMDL reductions for point

sources. Nutrient trading opportunities for ag?

• EPA goal - 45% reduction in N and P in the Mississippi River basin. MN is one of 12 states developing nutrient reduction strategies to meet it. Ultimate impact on agriculture?

• Crop agriculture is not mandated to make any changes now, but changes will obviously be needed eventually if a significant reduction is to be achieved.

• We want to make sure any changes are cost-effective!

PROJECT GOALS• Assess nonpoint source nitrogen contributions to

Minnesota rivers from a) the primary land use sources, and b) the primary hydrologic pathways under dry, average and wet climatic conditions

• Determine the watersheds which contribute the most nitrogen to the Mississippi River, and combination of land uses and hydrologic factors having the greatest influences on the elevated nitrogen

• Develop a nitrogen planning tool to estimate reductions in N loadings to surface waters at the watershed scale with various BMPs, and their costs

Agroecoregion Based N Database• Point data are available for crop

acreage and livestock numbers

• County statistics are available for crop harvest and N fertilizer use

• N transformations in soil (mineralization, denitrification) and N losses (volatilization, leaching, drainage, etc) are based on soil and landscape factors (represented by agroecoregions)

• Our approach is to estimate N inputs and outputs for agroecoregion units and then transform results back to watershed units

N Loadings to Surface Water by Source

Effect of Climate on N Loadings

Watershed N Reduction Planning Tool

• The Tool is an Excel spreadsheet linked to a database of Minnesota soils, landscapes, cropping systems, management practices and crop enterprise budgets

• Estimates of N reductions are based on research meta-data and BMP specific reduction coefficients

• Estimates are tied to site specific characteristics such as soil, slope, climate, and baseline farm management practices and cropping systems

N Reduction Planning Tool BMPs • Rate and timing of N fertilizer• Controlled drainage• Bioreactors• Planting cover crops• Planting perennial grass• Installing riparian buffer strips• Installing wetlands

• Effects of individual BMPs as well as combinations of BMPs can be evaluated

Suitable acres for BMPs• Fertilizer rate reductions are only possible in areas where

existing application rates exceed University recommendations

• Controlled drainage and bioreactors can be installed on tile drained land with slopes of 0.5%, 1% or 2%

• Perennial grass can be planted on ag land with crop productivity ratings of 60% or less (marginal land)

• Riparian buffers can be installed on ag land within 30 m of waterways

• Wetlands can be restored on tile drained land with hydric soils and high Compound Topographic Index values

“Effectiveness” is expressed as the N load reduction compared to the status quo. “Cost” is expressed per pound of N removed.

Adoption rates: Apply N at recommended rate on 90% of corn; shift 90% of fall-applied N to half preplant and half split preplant/sidedressed; plant riparian buffers on 70% of suitable acres; adopt controlled drainage on 90% and install bioreactors on 10% of tiled land of 1% or less slope; restore wetlands on 78% of suitable acres; plant rye cover crops on 70% of corn and soybean acres; and shift 27% of marginal land to a perennial crop.

0%

5%

10%

15%

20%

25%

30%

Optimal fertilizerrate and timing

Fert. mgmt + tiledrainage BMPs

Fert. mgmt + tileBMPs + vegetation

BMPs

Redu

ction

in N

Reducing N to Waters from Cropland Statewide

Vegetation changes

Tile drainage BMPs

Fertilizer mgmt.optimized

Cost saving

$81 Mi l lion

$1.3 Bi l lion

$81 Mi l lion

Cost saving

Cost saving

Conclusions

• Total nonpoint source N loadings to Minnesota surface waters were estimated at about 6% of the total inputs of N on all Minnesota cropland.

• Statewide, losses of N to surface water from agricultural sources represent 88% of total nonpoint source losses.

• A tool was developed to assist planners evaluate strategies for reducing N loadings to Minnesota surface waters, by target watershed, climate, and extent of adoption of various N reduction BMPs.

Conclusions

• Analysis so far shows that achieving N load reductions greater than 25% would be challenging.

• Implementation of N reduction strategies by the EPA and the states could mean some significant changes for crop agriculture. Stay tuned!

Thank you

• Support for this research was provided by the MN Pollution Control Agency

Download paper at: z.umn.edu/nbmppaper