# Presentation: 082389

## Use of nitrogen-15 natural abundance method,

***other tracers, and water chemistry ***
***to evaluate movement of irrigated treated wastewater through loess soils, Dodge City, Kansas***** **
- M.A. Townsend, M. A. Sophocleous, S. A. Macko,
- R.Ghijsen, M. Magnuson, and D. Schuette
- NRCS Personnel: J. Warner, S. Graber, R. Still, T. Cochran; C. Watts
- NRCS Conference 2008

## Site description

- Evidence of macropores in soils
- Soil profiles of nitrate and chloride
- Water quality at site
- 	variability
- Nitrogen-15 isotope background
- Nitrogen-15 isotope results
- 	groundwater
- 	soils and lysimeters
- 	plants

## Slide 3

## Slide 4

## High Plains Aquifer

- Overlain by loess
- Soils are silt loams
- Macropores (indicated by dye tracing) permits preferential flow
- Depth to water ranges from 75 ft to 120+ ft
- Groundwater flow from west to east
- Rainfall approximately: 16-20 in/yr
- Evaporation approximately: 30 in/yr

## Slide 6

## Slide 7

## Soils

- Evidence of Macropores

## Minimum or no tillage practice

- Minimum incorporation of pesticides and fertilizers to soil
- Increased soluble chemicals in surface flow that can enter macropores
- Plant residues on the surface and no tillage
- enhance worm activity
- allow worm holes and other macropore channels to 	stay open at the surface

## Results from Dye Tracing

## Slide 11

## Slide 12

## Slide 13

## Slide 14

## Water Quality

- Overall chemistry

## Slide 16

## Water Quality

**Tracers**

- Boron and Chloride

- Sulfate and Chloride

- Bromide/Chloride and Chloride

## Slide 18

## Slide 19

## Slide 20

## Kendall test for trend

- Nitrate-N
- Chloride

## Slide 22

## Slide 23

## Slide 24

## Slide 25

## Nitrogen-15 Natural Abundance Method

## 15N (‰) = [(15Nsample/14Nstandard air) – 1] x 1000

- Occurrence of Nitrogen Isotopes in air:
- 0.37 % 15N
- 99.63 % 14N

## Slide 28

## Slide 29

## Slide 30

## Y8, Irr

**Y8, Irr**

## Soil Nitrogen

- Soil-Water Lysimeters

## Slide 33

## Slide 34

## Soil Water Nitrate-N mg/L

## Slide 36

## Wastewater

**Wastewater**

**Fertilizer only**

## Summary of Results

- 1) Yearly nitrate-N and chloride show an increasing trend 	at most of the monitoring wells (1985-2005).
- 2) Decreasing trend of nitrate and chloride observed at 	edges of the irrigated fields suggesting possible dilution 	effects occurring over time
- 3) Boron, sulfate, and Br/Cl are good indicators of mixing of wastewater and ground water and evapoconcentration
- 4) Macropore flow impacts nitrate-N distribution in soil
- 5) Nitrogen-15 values support idea of macropore flow in the soils (higher lysimeter values than soil nitrogen)

## Summary of Results (cont.)

- 6)** ******15N values of ground water are different seasonally
- 		(fall versus spring)
- 7) Differences in values may be related to:
-      a) recharge of fertilizer irrigation (pre-1986)
- 		increased wastewater application (post-1986)
-      b) seasonal impacts of varying wastewater temperatures			cold versus warm temperature impacts on bacterial 			nitrification rates
- 8) Plants utilize the wastewater as indicated by the δ15N values

## Acknowledgments 

**Acknowledgments **
_**KWRI**__: _Funding source
_**NRCS**_: J. Warner, S. Graber, R. Still, T. Cochran; C. Watts
_**Servi-Tech**_: David Shuette; Fred Vocasek
_**KSU-Extension**_: Fay Russett
_**OMI (Dodge City):**_ Peggy Pearman, Cliff Mastin
_**Farm operator**_: Chuck Nicholson
_**KGS**__:_ J. Healey, B. Engard, D. Thiele; J. Charlton
_**Grad. students**_: Ashok KC (KGS current), Nick Schneider		Amanda Feldt (KSU-Extension)	**	**

## Questions?

## Slide 42