AZdrip: Long-term Evaluation of SDI Tom Thompson Dept. of Soil, Water, and Environmental Science Presented at Drip Irrigation Field Day Maricopa Agricultural Center, 7 July, 2005

AZdrip  “AZdrip”—long-term subsurface drip irrigation demonstration and research project located at the Maricopa Agricultural Center  Features: Large plots (70’ x 400’) 3 acres total Two drip tubing configurations: - 3 lines per permanent 80” bed - 1 line per 40” bed (or 2 lines per 80” bed) - Furrow-irrigated plot included for comparison High and low irrigation frequencies Long-term monitoring of crop yield and quality, economic returns, nutrient and chemical use, soil properties, salt build-up, and nutrient depletion in root zone.

Field Plan

Bed Configurations

 High frequency irrigation scheduling: Between 8 am and 8pm: Five 12” tensiometers in each of the high-frequency plots are read and averaged automatically every hour. If average reading is >10 cbar, irrigation is turned on for 30 min (0.07”). Cycle is repeated every hour. Irrigation Management (1) With “high-frequency” irrigation, automated tensiometers achieve real- time irrigation control

Irrigation Management (2)  Low frequency irrigation scheduling: When the average of 5 manual tensiometers in each low-frequency plot reaches cbar, 0.5 to 1.0” of water are applied. Frequency is every 3-7 days. With “low-frequency” irrigation, standard tensiometers are used to schedule ” irrigations

AZdrip Installation Costs  “Scaled up” to a 100 acre installation, broken up into six 16 acre blocks: 3 lines per permanent 80” bed,$ 2050/ac high frequency irrigation 1 line per 40” bed, high frequency$ 1833/ac irrigation 3 lines per permanent 80” bed, $ 1947/ac low frequency irrigation 1 line per 40” bed, low frequency$ 1730/ac irrigation

AZdrip Water Quality pH8.0EC (dS/m)1.6 NO 3 -N (ppm)6.0HCO 3 - (ppm)171 Na (ppm)240SAR7.1

Water Treatment/Chemigation  Irrigation water quality is monitored weekly. Irrigation water is continuously acidified to pH 6.0 with sulfuric acid.  Nitrogen is applied as UAN-32 solution.  Phosphorus is applied as solution.

Watermelon Commercial Harvest Yield July 2, 2005

Water Use

Water Use Efficiency

Benefits of SDI  Ease of harvest, field operations  Lower water use  Better crop uniformity  Reduces soil tillage—improved soil tilth  More flexible management options— frequency of irrigation/fertigation  Higher yields

Limitations of SDI  Initial cost  Salt management, especially with small- seeded vegetable crops  Time/cost for repair of drip tubing damage  High level of management expertise and maintenance is necessary

Summary of AZdrip Results,  Generally higher yields with SDI.  Generally higher yields with high-frequency SDI compared to low-frequency SDI.  Higher water use efficiency with SDI—even under conditions favoring high water use efficiency with surface irrigation.  After 5 seasons, the SDI system continues to perform well.

Acknowledgements  Colleagues participating on this project: Ed Martin, Russ Tronstad, Mary Olsen, Jim Walworth, Pat Clay, Kai Umeda  Funding by the University of Arizona Technology and Research Initiative Fund (TRIF), Water Sustainability Program

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