Monitoring near Surface Soil Water and Associated Dynamics of Infiltration and Evaporation Fluxes

1. Monitoring near Surface Soil Water and Associated Dynamics of Infiltration and Evaporation Fluxes Robert C. Schwartz1, Alan J. Schlegel2, R. Louis Baumhardt1 Steven R. Evett1 and Troy Dumler2 1USDA-ARS, Bushland, TX 2KSU Southwest Research–Extension Center Tribune, KS / Garden City, KS

2. Motivation Wheat Sorghum Winter wheat-sorghum-fallow rotation under stubble-mulch tillage (ST) and no tillage (NT) Fallow Winter wheat grain yield not usually influenced by tillage (NT vs. ST) Significant sorghum grain yield response to tillage in Tribune, KS but not in Bushland, TX

3. Motivation Historical dryland sorghum grain yields within a winter wheat-sorghum-fallow rotation under stubble-mulch tillage (ST) and no tillage (NT) 1Bushland yield and precipitation data from 1984 – 2009 on level terraces. 2Tribune yield and precipitation data from 1991 –2009.

4. Motivation • Dryland sorghum acreages: Adoption of NT in North Texas High Plains (5%) lags behind West Central Kansas (24%) • Economic returns: • Bushland: NT - $90 ST - $109 • Tribune: NT - $190 ST - $59 • Predominant soils Clay loam Silt loam

5. Motivation • Available soil water during the growing season dominates the yield response • Available soil water influenced by soil x tillage interaction • What are the hydrological drivers at each location that lead to differences in available soil water and the diverging yield response? • Do precipitation-evaporation-storage processes vary with respect to rotational phase? Infiltration Transpiration & Evaporation

6. Motivation • Soil Water Storage near surface (0 – 30 cm) • Neutron probe – accurate mass balance but unable to capture dynamics • Time Domain Reflectometry (TDR) – hourly measurements permit tracking of changes in stored soil water attributable to precipitation or evaporation

7. Objectives Bushland, TX no-till • Use of a water balance method to estimate infiltration and evaporation/ transpiration fluxes using TDR (Schwartz et al. 2008; 2010) sweep till sweep till • Compare tillage effects on these fluxes at both locations • Prior to sorghum emergence • Summer fallow after grain sorghum Tribune no-till

8. Methods • In 2006, TDR probes & thermocouples installed in field at 5, 10 15, 20, and 30 cm (2 x 106 measurements) • Neutron gage measurements of soil water – weekly to 2.4 m • 6 plots in Bushland / 3 plots Tribune • Meteorological measurements in field Cable Tester Multiplexers

9. Soil water balance components calculated for each plot With a knowledge of the change in storage, we can calculate evaporation as the difference Infiltration based on changes in storage during precipitation Drainage based on fitted field hydraulic properties at the lower boundary, measured water contents above and below this depth, and the calculated gradient and Darcy flux

10. Water contents – sorghum after wheat – Tribune, KS (2006) No tillage 37 mm more infiltration 25 mm more storage similar evaporation losses

11. Water contents – sorghum after wheat – Bushland, TX (2007) No tillage 6 mm less infiltration 13 mm more storage similar evaporation losses

12. Water Contents – Fallow after sorghum – Bushland, TX (2008) • Single tillage operation • Drainage based on water contents at 50 and 70 cm • Greater water contents at 5 and 10 cm under NT

13. Cumulative Fluxes – fallow after sorghum – Bushland, TX (2008) Change in storage at 0 – 60 cm • Drainage negligible • Similar infiltration & evaporation fluxes • Stored soil water: • DOY 153 • NT + 5 mm > SMT • DOY 217 • NT + 12 mm > SMT • Large variability among NT plots for infiltration and evaporation fluxes

14. Residue above TDR probes, Bushland, TX (DOY 189) Plot 7 Runon No Tillage Plot 2 Runoff Plot 5 Runoff Stubble Mulch Tillage

15. Tillage effects in the absence of residue (Bushland, TX) • Soil sealing is problematic under low residue cover that is temporarily ameliorated by tillage • Aggregate response represents varying residue amounts throughout the field, especially for NT

16. Water Contents – Fallow after sorghum – Tribune, KS (2007) • Two tillage operations • Drainage based on water contents at 91 and 122 cm • Greater water contents at 5 and 10 cm under NT • Weed growth prior to herbicide application

17. Cumulative Fluxes – fallow after sorghum – Tribune, KS (2007) Change in storage at 0 – 107 cm • Drainage fluxes large • Greater NT infiltration & evaporation fluxes • Stored soil water: • DOY 117 • NT + 20 mm > SMT • DOY 217 • NT + 14 mm > SMT • Large variability among NT plots for infiltration and evaporation fluxes

18. Tillage effects on cumulative infiltration for selected precipitation events Bushland Tribune

19. Precipitation and evaporative cycles (Bushland, TX) Evaporation – calculated in 1, 3, 5 and 10 day intervals Evaporation, mm d-1

20. Precipitation and evaporative cycles (Tribune, KS) Evaporation – calculated in 1, 3, 5 and 10 day intervals weeds Evaporation, mm d-1

21. Conclusions • Areas of high residue / micro-lows contributed to large variability in fluxes for NT at both locations • Tillage reduced pre-emergence water content by 10 mm (Bushland) and 60 mm (Tribune) • Most additional stored water under NT is near surface (< 15 cm) • Marginal increase in soil water storage under NT (10 mm) compared with ST during summer fallow

22. Conclusions • Bushland – no consistent tillage effect on cumulative infiltration and evaporation rates; drainage negligible • Fine-textured soil = low infiltration rates • Lower wheat yields + warmer climate = less residue • Tribune – NT significantly increased infiltration compared with ST but these gains were offset by greater evaporation and drainage rates below 60 cm • During the growing season in Tribune, a proportion of evaporative and drainage fluxes under NT would be diverted to transpiration

23. Acknowledgements Jourdan Bell Grant Johnson Jeff Slattery