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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
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18 20
Nit
rate
Co
nce
ntr
atio
n (
pp
m)
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.
0
5
10
15
20
25
5/5/2017 5/25/2017 6/14/2017 7/4/2017 7/24/2017 8/13/2017 9/2/2017 9/22/2017 10/12/2017
Nit
rate
Co
nce
ntr
atio
n (
pp
m)
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!