This paper provides exerpts from a case study of the conversion of a Thompson Seedless grape vineyard from flood irrigation to surface drip (SDI) and subsurface drip (SSDI) irrigation systems. The case study report was prepared jointly by a commercial gr ape grower and staff researchers from the Center for Irrigation Technology (CIT) at California State University, Fresno. The vineyard is located at the southeast corner of Shaw and Goldenrod avenues in western Fresno County, California and is operated by S.E. Lehman Farming Enterprises. It was established in 1910 and has undergone conventional flood irrigation treatments.
EVOLUTION OF DRIP IRRIGATION
Drip irrigation systems have evolved significantly in the last several years. Hydraulic performance of system components is far more predictable, and most materials have a demonstrated useful life of more than 20 years. Further, problems associated with diminished hydraulic capacity over time have been solved by a combination of proper screening, flushing, and chemical treatment as well as improved emitter design. In the wake of these component improvements, the irrigation industry now faces new questions related to the application of complete surface and subsurface drip systems to specific crops (in this case a vineyard producing raisins for drip irrigation syste ms). These questions, all of which impact the overall profitability of an agricultural operation, must be addressed by both equipment manufacturers and farm producers. In the area of system design, operation, and maintenance, these questions are concerned with:
- Adopting bench test and design data to meet field conditions.
- Developing practical and effective water management schemes.
- Verifying the adequacy of the design and water management schemes.
- Adopting conventional farming practices to meet the unique requirements of drip systems.
- Developing reliable methods of comparing surface vs. subsurface dripline placement.
In the area of crop physiology, questions involve:
- Adaptation of the root mass to changes in application patterns and irrigation timing.
- Rooting patterns that affect system hydraulic performance.
- Impact on root zone and canopy disease.
- Impact on crop production and quality.
Operation of the SDI and SSDI systems in this case study has extended through three complete cropping seasons (1993-1996). Selected performance data has been developed and records maintained to allow at least a partial answer to the previously-raised que stions. Answers will be refined as the systems function through the 4th and 5th cropping years. Plant physiology and rooting questions will be addressed by studies currently under way.
MATERIALS AND METHODS
All surface located driplines are placed at the base of the vines. All buried driplines are located offset approximately 24 in. from the vine row on the north side and buried approximately 18 in. The installation incorporates modern drip irrigation technology for vineyards and features the following components:
- Turbulent flow non-pressure compensated emitters (Drip In) mounted integrally within the dripline. Spaced 42 in. c/c, the emitter advertised flow rate is 0.65 gph at 15 psi. Emitters to be installed in the buried plot were impregnated with Root Guard. Root Guard is a patented process engineered to inhibit roots from entering the emitter for approximately 20 years. The active compound is a pre-emergence herbicide called Gowan Trifluralin 5. These emitters were installed on approximately 9.37 acres of s urface and 9.37 acres of sub-surface drip irrigation systems. The driplines are manufactured by Drip In (Geoflow), Fresno, California.
- Pressure compensated emitters (RAM) mounted integrally on the inside wall of the dripline. Spaced 42 in. c/c, the emitter advertised flow rate is 0.61 gph over a range of pressures from 7 to 60 psi. The emitters were installed on approximately 9.37 ac res of surface and 8.84 acres of sub-surface irrigated vines. The driplines are manufactured by Netafim Irrigation, Inc., Fresno, California.
- Sub manifolds for the turbulent flow (Drip In) emitters were equipped with 3/4 in. pressure regulating valves at the inlet to the driplines. The system is protected from excessive pressure by a 3-in. pressure relief valve. Automatic control to the fou r blocks is accomplished using 3-in. electrically actuated control valves. Overall system pressure regulation is achieved using a 4-in. pressure relief/sustaining valve. These valves were all manufactured by Bermad of Anaheim, California.
- Filtration for the system was provided by a 3-tank sand media filter assembly. The tanks are 36 in. in diameter and fabricated from stainless steel. They feature automatic backflush control. A No. 20 sand is used as the media. Disposal of backflush wa ter is accomplished by a unique slotted pipe located in a soak away area. The media filter system was manufactured by the Claude Laval Corporation of Fresno, California.
Other component features of the system include the following:
- Use of air vent and plastic ball valves on all submain manifold control
- 20-in. flow meters provided on each of the four blocks
- Mainline 2-in. air vent valves
- Venturi chemical injection assembly using an auxiliary 1.0 hp pump
- A 400-gallon poly tank for storage of chemicals to be injected into the system
- A hopper system for injecting granular chemicals
FULL CASE STUDY AVAILABLE
The complete case study report of this project is available from the Center for Irrigation Technology. It is titled, "Progress Report on the Lehman Farms Project: A Case Study in the Conversion on an Old Vineyard from Flood to Surface Drip (SDI) and Subsurface Drip (SSDI) Irrigation." Authors are D.F. Zoldoske, director of CIT, and E.M. Norum, spcial projects engineer for CIT. The report contains 130 pages and costs $29.50. For ordering information, contact CIT at (209) 278-2066.