W. Adam Sigler

1. The Big Levers - Management, Soils, and Weather Interactions controlling soil water and nitrate loss in a non-irrigated cropping system Funding USDA/NIFA National Integrated Water Quality Program MSU College of Agriculture MSU Office of the Vice President of Research Montana EPSCoR MSU Extension Water Quality Montana Fertilizer Advisory Committee W. Adam Sigler Stephanie A. Ewing Clain A. Jones Robert A. Payn Marco Maneta Perry Miller Primary Field Technicians Simon Fordyce Kyle Mehrens Robby Robertson, MSU/BSWC MT AWRA; October 19th, 2018

2. Broader Project Goals To better understand the sources of nitrates in ground and surface water To evaluate which management practices are likely to be effective to reduce nitrate leaching and to be adopted To engage the local community in participatory research to meet the first two goals M1 Nitrate-N Judith Basin Nitrogen Project Today’s Talk How do agricultural management, weather, and soils interact to control deep percolation and nitrate leaching?

3. Acknowledgments Advisory Committee Tom Butcher: Producer, Fergus County Rick Caquelin : MT NRCS, Central MT Region Range Specialist Chrissy Cook: MSU Extension, Judith Basin County Darren Crawford: MSU Extension, Fergus County Patricia Creamer: MT NRCS, Judith Basin Dist. Conservationist Pat Hensleigh: Montana NRCS, State Agronomist, Bozeman Curtis Hershberger: Producer and owner of NGS Sales, Denton Jane Holzer: Montana Salinity Control Association Mark McLendon: NRCS Soil Conservationist, Lewistown Terry Metcalfe: Producer, Benchland Deen L. Pomeroy, RS: Central Montana Health District Ken Ronish: Fergus County Commissioner, Denton David Wichman: CARC, Superintendent and Agronomist Producer Research Advisory Group Nita Bronec Greg Grove Jim Kulish Dave Linker Brandon Morris Bing VonBergen Publications Jackson-Smith D, Ewing S A, Jones. C A, Sigler W A and Armstrong A (in press) The road less travelled: Assessing the impacts of in-depth farmer and stakeholder participation in groundwater nitrate pollution research. J. Soil Water Conserv. John, A.A., Jones, C.A., Ewing, S.A., Sigler, W.A., Bekkerman, A., Miller, P.R., 2017. Fallow replacement and alternative nitrogen management for reducing nitrate leaching in a semiarid region. Nutr. Cycl. Agroecosystems 1–18. Sigler, W.A., Ewing, S.A., Jones, C.A., Payn, R.A., Brookshire, E.N.J., Klassen, J.K., Jackson-Smith, D., Weissmann, G.S., 2018. Connections among soil, ground, and surface water chemistries characterize nitrogen loss from an agricultural landscape in the upper Missouri River Basin. J. Hydrol. 556, 247–261.

4. Research Question How do agricultural management, weather, and soils interact to control deep percolation and nitrate leaching? Study Area Moccasin Terrace Judith Watershed Field C

5. Management, Weather, Soils Grower Standard Practice is a three year rotation Year 1: Spring Grain Year 2: Summer Fallow Year 3: Winter Wheat Bauder et al. 1993 Year 4: Spring Grain Year 5: Summer Fallow Year 6: Winter Wheat High Leaching Risk Chemical Summer Fallow = plant growth suppressed for a full year with herbicide

6. Management, Weather, Soils Crop Sequence Categories • Fallow- • Crop- • Crop- • Crop • Crop • Fallow (FC) (CC) (CF)

7. Management, Weather,Soils Seasonal Variation in Precipitation and Reference Potential Evapotranspiration

8. Management, Weather, Soils North Catchment South Catchment (ToF ~ 61 cm) (ToF ~ 131 cm) Thickness of Fines (ToF)

9. Management, Weather, Soils Field C

10. Hydrus 1D – Water movement through variably saturated soil Richards Equation Input Precipitation Potential Evaporation Potential Transpiration Soil horizon hydro param (van Genuchten) Output Soil moisture content Water flux • van Genuchten Equation Parameters (to implement Richards) • Θr - residual soil water content (L3/L3) • Θs - saturated soil water content (L3/L3) • α - corresponding approximately to the inverse of air-entry matric potential or bubbling pressure (1/L) • n – pore size distribution index (dimensionless) • Ks – saturated hydraulic conductivity (L/T) • l – pore connectivity/tortuosity parameter (dimensionless), assumed to be 0.5 by Mualem 1976 Richards Eq is in terms of water pressure; for mass balance, we need to convert pressure to water content.

11. Model Soil Configuration Fines (clay loam) van Genuchten • Θr = 0.08 (L3/L3) • Θs = 0.44 (L3/L3) • α = 0.02 (1/L) • n = 1.41 (dimensionless) • Ks = 8.18 (L/T) Gravel (sand) van Genuchten • Θr = 0.05 (L3/L3) • Θs = 0.37 (L3/L3) • α = 0.04 (1/L) • n = 3.2 (dimensionless) • Ks = 640 (L/T)

12. Model Calibration

13. Modeling to Address Research Question Management (3 rotation scenarios) Weather (15 years) Period of available Agrimet data Soils (30 depth increments) = 90 model scenarios for 3 year rotations with fallow over variable ToF

14. Modeled Precipitation Partitioning by Crop Sequence Category Storage Transpiration Evaporation Deep Percolation Each bar is the mean of 15 years of model results

15. Nitrate Concentration by Crop Sequence Nitrate Sources Fertilizer: Mineralization: High High High Low 0 High

16. Model Results by Crop Sequence Category Deep Percolation (cm yr-1)

17. Field CModel Results Preliminary Results Modeled Deep Percolation (cm yr-1) Modeled Nitrate Leaching (kg N ha-1 yr-1)

18. Catchment Scale Model Results Preliminary Results

19. Management Soils ToF = 55 Precipitation Fallow-Crop Conclusions Leaching risk is highest during fallow and post-fallow periods ToF <40cm soils contribute disproportionately to leaching Heavy precipyrs dominate mean 15 year leaching rates Crop-Crop Crop-Fallow