Nitrate Reduction Strategies

Utilizing cover crops to reduce nitrate leaching,

increase nitrogen retention and protect water resources.

1. Nitrate research methods.

2. Nitrate behavior in Southeast Minnesota.

3. Cropping systems are part of the solution.

TOPICS

Streams

• Large and medium sized watersheds.

• Data gathered represents aggregate cropping systems and land uses.

• Long term sampling periods are preferred.

• Trends or sudden changes in results are valuable to correlation and causation.

NITRATE RESEARCH METHODS

NITRATE RESEARCH METHODS

Springs

• Large and medium sized watersheds.

• Data gathered represents aggregate cropping systems and land uses.

• Long term sampling periods are preferred.

• Trends or sudden changes in results are valuable to correlation and causation.

• Spring response to landscape or climate varies by geology. Response may be minutes to days.

NITRATE RESEARCH METHODS

Tile Drainage

• Medium or Plot Scale

• Data gathered can represent specific crops, rotations and management.

• Fast response times to cropping system and climate.

NITRATE RESEARCH METHODS

Lysimeters

• Made from PVC with porous ceramic tip. Vacuum drawn prior to sampling

• Plot and Micro Scale contribution area.

• Data gathered can represent specific crops, rotations and management.

• Fast response times to cropping system and climate.

• Variability between samples can occur, but large sample numbers provide accurate, high resolution data.

NITRATE BEHAVIOR

• Multiple Agencies and Universities have studied nitrate concentrations below different land covers, septic systems and municipalities. (MPCA, DNR, MDA, U of M and SWCDS.)

• Well known and predictable Nitrate results in groundwater, tile discharge and streams. Example: Watkins Curve

• Corn and Soybeans are inherently nitrate “leaky” crops. They lack the physiology to keep nitrates from leaching below the rooting zone.

• Even when using the right rate, time and method of Nitrogen application, concentrations below the rooting zone will be higher than 10 ppm.

WATKINS CURVE

OLMSTED COUNTY SOIL HEALTH FARM

• 55 Acres

• 6 Replicated Plots

• Demonstration Area

• 12 Lysimeters

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Nit

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ntr

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Growing Week (May – October)

Olmsted County Lysimeter Results (2016 – 2018, 382 samples)

2018 – Corn27.5 ppm averagen = 132 samples

2016 – Corn 15.9 ppm averagen = 48 samples

2017 – Soybean 10.8 ppm averagen = 224 samples

BEAR SPRING STUDY AREA

OLMSTED COUNTY FAIRGROUNDS

BEAR SPRING

HIGHWAY 52 ROCK CUT

GEOLOGY

• Predominately Prosser

Limestone

• Shallow, Highly Fractured,

Solution Enlarged Conduits

• Shallow, Light Soils

CATCHMENT

AREA

Dye tracing, bedrock topology, surface topography, anticlines and synclines.

BEAR SPRING DATA

• FLOW

• TEMPERATURE

• NITRATE

• PRECIPITATION /

SNOWMELT

• GROUNDWATER

ELEVATION

15 Minute intervals

averaged over 1 hour.

2018 LAND USE

LAND USE ACRES% OF

TOTALEXPECTED NITRATE

Corn 1,037.4 59% 27Alfalfa 203.2 12% 1.6

Soybeans 202.5 12% 11Road 95.7 5% 0

Perennial Grass 52.1 3% .7Grove 45.6 3% .7CRP 39.3 2% .7

Farmstead 36.2 2% 6Wooded 25.0 1% 1.2

Lawn 12.5 1% 6Feedlot 0.4 0.02% 20TOTAL: 1,749.9 100% 19.4 ppm

Corn

Alfalfa

Soybeans

Road

Perennial Grass

Grove

CRP Farmstead

WoodedLawn

Feedlot

Roughly 71% of the Bear Springshed was planted to Corn and Soybeans in Crop

Year 2018.

Using Soil Health Farm Lysimeter data and other sources, we may expect

Nitrate concentrations to be 19.4 ppm at Bear Spring.

• Actual nitrate concentrations are measured between 19 and 20 ppm during baseflow.

• Concentrations are as high as 26 ppm during wet / storm periods.

Bear Spring Data – 2016 - 2018

9.25” from June 9 – July 14

1,300 gpm to 4,500 gpm

22 PPM dilutes to 12.2 ppm

Over – corrects to 24.5 ppm

1.47” of RainJune 27

Baseflow: Approx 500 gpm

During the 24 hours of June 281,520 lbs of nitrate discharged from bear spring. (63 lbs / hr or $35.00 / hr)

Majority of Studies confirm that nitrate reductions range from 20-60% with adoption of cover crops into a cropping system. Studies span many years, locations and methods.

Actual reductions of Nitrate vary due to vegetative growth and climate.

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Soybean Year Lysimeter Results (224 Samples)

With Cover Crops Without Cover Crops

Average Nitrate Without Cover Crops: 13.1 mg/L

Average Nitrate With Cover Crops: 8.8 mg/L (33% reduction)

2017 OLMSTED SOIL HEALTH FARM

Most nitrate tie-up from winter rye occurs in spring when [Rye] is actively growing and precipitation rates are high…

Following termination, the winter rye begins to decompose when cash crops are actively consuming nutrients.

1.Remove 200 acres of Corn and plant Alfalfa

2.Adopt Cover Crops on 100% of the Corn and Soybean Acres.

LAND USE ACRES% OF

TOTALEXPECTED NITRATE

Corn 837.4 48% 16.2Alfalfa 403.2 23% 1.6

Soybeans 202.5 12% 6.6Road 95.7 5% 0

Perennial Grass 52.1 3% .7Grove 45.6 3% .7CRP 39.3 2% .7

Farmstead 36.2 2% 6Wooded 25.0 1% 1.2

Lawn 12.5 1% 6Feedlot 0.4 0.02% 20TOTAL: 1,749.9 100% 10.1 ppm

2 MANAGEMENT CHANGES1. Remove 200 acres of Corn and

plant Alfalfa2. Adopt Cover Crops on 100% of

the Corn and Soybean Acres.

The expected Nitrate drops to 10.1 ppm. THIS

IS THE BENCHLINE!!

Corn

Alfalfa

Soybeans

Road

Perennial Grass

GroveCRP

Farmstead Wooded Lawn Feedlot

Deep, Fibrous Roots!