Automatic Irrigation Scheduling of Grain Sorghum Using an Integrated CWSI

1. Automatic Irrigation Scheduling of Grain Sorghum Using an Integrated CWSI S.A. O’Shaughnessy, S.R. Evett, P.D. Colaizzi, and T.A. Howell USDA-ARS Bushland, TX USA 5th Decennial Irrigation Association Conference December 5, 2010

2. Introduction • Irrigation scheduling using remote ground-based and in-situ sensors will be a key element to irrigation automation. • As of recent, our interest has been in the theoretical CWSI, a stress index developed by: • Jackson et al., 1981 • and utilized for irrigation timing for a variety of different crops to include corn, wheat, alfalfa, and sorghum; • however its performance has been marginal.

3. Objectives • Investigate the usefulness of the CWSI as a trigger for automatic irrigation scheduling over: • a relatively long period of time • and frequently over the growing season. • Analyze sorghum yield response to automated vs. manual methods of irrigation; • Examine water use efficiency at deficit irrigation levels.

4. Materials Field Layout for 3 span center pivot system

5. Materials Cont’d: • Sensors • Infrared thermometers on pivot lateral and within cropped field • Meteorological instruments- RH, air temperature, wind speed, and short wave radiation pyranometer anemometer infrared thermometers

6. Center pivot as a platform for sensors

7. Methods • Crop was planted in concentric rows, spaced 0.76 m apart • LEPA irrigation in every other furrow using drag socks • Rows were furrow-diked • Manual pie sections were irrigated over odd DOY to replenish soil water depletion (based on weekly neutron probe measurements) in the top 1.5 m • Automatic pie sections were irrigated on even DOY, if an irrigation signal was received

8. Methods cont’d: • An irrigation signal was scheduled for the automatic treatments if: • CWSI ≥ 0.45 for a cumulative time threshold ≥ 420 min in a 24 hour period. • Irrigation Treatments were 80%, 55%, 30%, and 0% of twice the daily peak water use

9. Methods cont’d: • Calculation of CWSI

10. Calculation CWSI cont’d: Theoretical approach- (Jackson, et al., 1981) ra = ln [(z-d)/zo]/k2/U, Upper Limit: Lower Limit:

11. Efficiency Calculations: Water use efficiency: Irrigation water use efficiency (IWUE, kg m-3): where Ygi is the economic yield (g m-2) from irrigation treatment level i, Ygd is the I0% yield (g m-2), and IRRi is the irrigation water applied (mm) (Howell, 2001).

12. Results

13. Average difference in early-season soil water levels (Manual -Automatic Treatment Plots)

14. Climatic conditions for the 2009 growing season Cumulative rainfall = 240 mm Boot Flowering Grain filling

15. Cumulative irrigations for the manual and automatic control methods plotted against time and key growth stages.

16. Grain Yield Response d, f f d e b p=.73 c p=.05 p=.03 a a p=.97

17. Comparative Water Use Efficiency

18. Irrigation water use efficiency per irrigation depth

19. Preliminary Conclusions • Repeated field trials are necessary with the same crop; this algorithm was tested on a long season grain sorghum in 2010. • Applied irrigation amounts between the manual and automatic methods were not significantly different • Remote identification of the hard dough stage would be beneficial to automatically terminate irrigations. • Additional testing on different crops and in different regions is required to validate the efficacy of this stress index as an irrigation trigger.

20. Acknowledgements • Funding from the • Ogallala Aquifer Program • National Sorghum Checkoff Program • The technicians at Bushland CPRL

21. Thank you for your attention!