The role of soils in nitrate leaching to groundwater Judith River Watershed, Montana

Transcription

1 CN1 The role of soils in nitrate leaching to groundwater Judith River Watershed, Montana Stephanie A. Ewing Michael Bestwick, Adam Sigler, Clain Jones, Katelyn Noland, Christine Miller Department of LRES, Montana State University Montana AWRA October 3, 2013

2 THE LARGER PROBLEM elevated groundwater nitrate is common in agricultural regions Burow et al., 2010 Young groundwater, high inputs, and well-drained soils

3 MORE LOCAL CASE STUDY: Judith River Watershed A B How has land use influenced groundwater nitrate in this region over time? How can we manage that effect sustainably given intimate C association of land use with local communities? dryland wheat production (99% of NGP) and livestock, common fallowing shallow unconfined aquifers, well drained soils, high nitrate levels, little BMP adoption

4 Rising nitrate-n concentrations in a monitoring well near Moccasin Blue symbols: Montana Department of Agriculture, Montana Groundwater Information Center (GWIC). Red symbols: Montana State University Environmental Analysis Laboratory. We know this is a longer term issue.

5 Rising wheat yields and and associated N fertilizer use in Montana data: USDA National Agricultural Statistics Service; USDA Agricultural Census How does management of soils influence water quality in shallow, unconfined aquifers?

6 Participatory research to evaluate and address sources of nitrate in groundwater Testing effects of management changes on nitrate leaching from soils dryland farmed for wheat (A. John, C. Jones et al.): Peas in place of fallow in three year rotation Timing of fertilizer application C B A Participatory approach to tackle the problem (D. Jackson-Smith et al.) Evaluating field and landscape scale hydrology as a driver of nitrate leaching from soils to groundwater (and surface water) (A. Sigler et al.) A Sigler

7 Soil sampling and instrumentation solute profiles and soil hydrologic monitoring mini-excavator = dream pits volumetric sampling, 15 cm increments to ~120-cm depth four sites paired across eight management boundaries on three landforms loess over alluvial gravels at cm depth

8 LATE SUMMER 2012: fallow stores mineralized ON as nitrate nitrate-n; gravel depth 31 kg N/ha; 82 cm 46 kg N/ha; 94 cm 48 kg N/ha; 73 cm 52 kg N/ha; 92 cm 41 kg N/ha; 100 cm ~30-60 kg nitrate-n/ha in fallow

9 LATE SUMMER 2012: peas draw down nitrate in the upper 50 cm ~ 20 and ~40 kg nitrate-n/ha

10 LATE SUMMER 2012: barley draws down soil nitrate to greater depth ~ 10 kg nitrate-n/ha

11 LATE SUMMER 2012: soil nitrate-n storage in fallow is ~0.5 kg N/ha-cm above gravel (should be non-linear)

12 Time series of cultivated vs. uncultivated nitrate, spring uncultivated-- --cultivated-- At cultivated sites, kg IN loss from upper soil in two weeks (leaching plus uptake) Noland et al. 2013

13 Ap C2E.01 depth to gravel: 80 cm A Bk1: 26 cm 2Bk2 2Bk3 2CBk

14 nitrate-n is % of TN 31 kg nitrate-n/ha 14,500 kg TN/ha depth to gravel: 80 cm (gradual increase) MSU Environmental Analysis Lab: Sample analysis for TN, TC, OC

15 OC/TN decreases from 12 to 2 with depth drop in OC below gravel contact 31 kg nitrate-n/ha 14,500 kg TN/ha 153,000 kg OC/ha depth to gravel: 80 cm (gradual increase) MSU Environmental Analysis Lab: Sample analysis for TN, TC, OC

16 drop in OC below gravel contact 31 kg nitrate-n/ha 14,500 kg TN/ha 153,000 kg OC/ha 475,000 kg IC/ha depth to gravel: 80 cm (gradual increase) peak in IC at gravel contact and below MSU Environmental Analysis Lab: Sample analysis for TN, TC, OC

17 Ap C3W.01 depth to gravel: cm (sharp boundary) AB Btk1 53 cm Btk2 2Bk 2CBk

18 MSU Environmental Analysis Lab: Sample analysis for TN, TC, OC nitrate-n is % of TN 52 kg nitrate-n/ha 15,600 kg TN/ha

19 OC/TN decreases from 10 to 6 with depth Native organic matter continues to supply N for agriculture Longer term water balance is reflected in the very large IC inventory 52 kg nitrate-n/ha 15,600 kg TN/ha 101,000 kg OC/ha 449,000 kg IC/ha depth to gravel: cm MSU Environmental Analysis Lab: Sample analysis for TN, TC, OC

20 How do apparent soil losses influence groundwater nitrate-n? Numerical model for Moccasin terrace annual timestep, kg N leached from soil annually, depending on rotation; kg N stored in soil (compare 5-60 obs) fertilizer crop yield F Y soil Sn B uptake into roots/stem s M net mineralization leaching groundwater Gn k L Sn dsn dt F M Y B k L Sn discharge Dw(Gn/Va) C. R. Miller et al. in prep.

21 C2E.01 Conclusions Nitrate depth trends in fallow reflect annual transient storage of mineralized ON Native soil fertility continues to supply N for crops Soil nitrate storage reflects depth to gravel, crop management, water balance Landform scale mass balance model of soil nitrate flux to groundwater suggests delayed response to management changes (decadal residence time and response)

22 Funding USDA/NIFA National Integrated Water Quality Program Montana State University College of Agriculture/MAES MSU Extension/Water Quality Program Montana Institute on Ecosystems/NSF EPSCoR Co-authors Adam Sigler, MSU Clain Jones, MSU Christine Miller, MSU Mike Bestwick, MSU Katie Noland, MSU MSU Environmental Analysis Lab Jane Klassen Hailey Buberl Erik Anderson Brent Zundel Key Collaborators Douglas Jackson-Smith, USU Gary Weissmann, UNM Judith Project Advisory Council Judith Project Producer Research Advisory Group Andrew John (Jones MS student, MSU) Ann Armstrong, USU Aiden Johnson (Stoy PhD student, MSU) Paul Stoy, MSU Jack Brookshire, MSU Perry Miller, MSU Rob Payn, MSU Kyle Mehrens, MSU/City of Bozeman Simon Fordyce, MSU Robbie Robertson, Americorps