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Reporting
Period: September 1999 to December 2000.
Objectives:
1. Modify
a center pivot irrigation system to provide variable quantities of
water in a pre-programmed manner as the unit circles a field.
2. Begin development of a delivery system for the spot application
of foliar agricultural chemicals along the length of a pivot.
A. Summary
of Progress:
Progress has been made on the first of the two objectives. Original
implementation plans called for the modification of four spans of a
center pivot located at Halfway. However, access to a larger pivot and
more land area at the Helms site resulted in moving this project to
the larger pivot at Helms. A standard commercial center pivot (Lindsey
Manufacturing, Lindsey, NE) 1360 feet in length was delivered in March
2000.
Water
Distribution System. Prior to the delivery of the pivot several variable
rate (VR) irrigation components were constructed and evaluated. A VR
manifold unit was suspended from a single span center pivot at Halfway
to evaluate options for construction and hydraulic performance. Based
on this evaluation, brackets and braces for the support of final manifold
units and electrical conduit were fabricated and galvanized. A modified
LEPA applicator was also developed to accommodate water flows from the
three manifolds of each manifold unit. Ninety-six LEPA applicators were
constructed to equip three spans of the Helms pivot for VR irrigation.
The system
design required water to be supplied from the mainline pivot lateral
through pressure regulators and solenoid valves to each of three manifolds
comprising the manifold unit. There are three manifold units per 160-ft
pivot span. Hoses are used to direct water from the manifolds to the
modified LEPA applicator. Initial nozzle sizes for each applicator provide
flow rates of 2x, 3x, and 4x which, in various combinations, will provide
6 discrete irrigation amounts ranging from 40 to 140% of a base irrigation
rate. Manifold units, hoses, and LEPA applicators have been installed
on Spans 6, 7, and 8 of the Helms pivot. Pressure regulator and valve
assemblies have been constructed and are currently being installed.
Figures
1 and 2. Elements of a variable-rate LEPA irrigation system being constructed
on the Helms pivot at the Halfway/Helms research site.
Water
Supply Equipment. Irrigation wells and pipelines are typically designed
for constant flow at relatively low pressures. VR irrigation can cause
drastic changes in flows and pressures within that water delivery system
due to valves being turned on and off at various preplanned locations
in the field. To address this problem, a pressure regulating system
(Cycle Stop model CSV3R, Lubbock, TX) and an interactive pivot safety
system were installed on one well supplying water to the VR Pivot. This
system provides a means to reduce pressure in pipelines and the pivot
as total irrigation volume is reduced. In initial tests, this system
provided constant outlet pressures (+/- 2 psi) over flow rates ranging
from 30 to 350 gpm. A booster pump at the pivot was installed to increase
pivot pressure if required. Variable speed controls for this pump will
be installed subject to need. An additional water well with pressure
regulation will be available prior to the 2001 crop season.
Control
System. The solenoid valves of each manifold unit are to be activated
relative to field location, thereby controlling irrigation quantities
at specific sites. A SNAP-LCSX-PLUS industrial controller (Opto 22,
Temecula, CA), two remote terminal units (SNAP-B3000), software, and
related accessories were purchased for this purpose. The control system
was programmed to provide four control signals to each manifold unit
(3 signals for the 3 water manifold solenoids and an additional signal
for a future chemigation actuator). Programming further allowed changes
in solenoid status every 30 around the 3600 perimeter of the pivot.
Therefore, the largest control area under this VR pivot will be less
then 0.1 acre (53' manifold unit length x 71' of a three degree arc)
resulting in over 2000 water/chemical control areas under this 133 acre
pivot. A standard incremental encoder (DynaparÔ Series E15) was
purchased to provide an input signal to the controller to determine
pivot location. A Microsoft ExcelÔ program was written to create
coded map files from irrigation application maps. Changing an application
sequence in the field will require developing a map file and transferring
this code directly with a laptop computer or by telephone modem to the
controller in the field. Installation of the control system and wiring
on the pivot is scheduled for January 2001. Preliminary testing and
evaluation of the system should occur in February and March 2001.
Figures 3 and 4. Schematic of the irrigation control areas and control
system components of the variable-rate pivot being constructed at Halfway/Helms.
B. Education/technology
transfer:
Bordovsky attended a 3-day irrigation control system workshop sponsored
by Eldar-Shany in Fresno, CA.
Invited presentations which contained elements of VR application research
conducted within this project:
Bordovsky, J. P. 1999. Irrigation system efficiency. High Plains Association
of Crop Consultants. Lubbock, TX.
Bordovsky, J.P. 2000. New research developments. Irrigation in Cotton
Production: Fundamentals, Management Strategies and New Developments,
Marriott River Center, San Antonio, TX.
Bordovsky, J.P. 2000. Irrigation research on the Texas High Plains.
Texas Agricultural Industries Association. Lubbock, TX.
Bordovsky, J.P. 2000. New research developments. Irrigation Update for
the High Plains. Texas Agricultural Irrigation Association. Amarillo,
TX.
C. Milestones
achieved:
March 2000 Helms center pivot was delivered. Support brackets for variable-rate
items were installed as the pivot was being constructed.
August
2000 - Installed and evaluated flow control valve on well.
Sept. 2000
- Finished development of preliminary software for the control of variable-rate
irrigator.
Oct. 2000
- Finished field construction of manifold units on outer three spans
of Helms pivot.
Dec. 2000
- Final cotton harvest completed in a 9-acre area used to evaluate a
position sensitive, multiple rate spray applicator for perennial weed
control (1997-99 funding period.)
D. Publications:
Bordovsky, J.P. and J.W. Keeling. 2000. Perennial weed management with
a position sensitive,
multiple-rate spray applicator. Proceedings 2000 Beltwide Cotton Conferences,
San Antonio, TX
399-404.
E. Precision
agriculture proposals:
Archer, T.L., R. Lascano, K. Bronson, and E. Segarra. (J. Bordovsky
- collaborator). 1999. Optimizing plant productivity using integrated
crop management in a precision agriculture system. NRI. Not funded.
Rush, C.M.
and J.P. Bordovsky. 1999. Development of a variable rate irrigation-chemigation
system for center pivots. ARP/ATP. Not funded.
Archer,
T.A., L.T. Wilson, R. Lascano, B. Payne, E. Segarra, J. Bordovsky, and
W. Xu. 2000. Optimizing plant productivity using site-specific crop
management. USDA - NRI. Not funded.
F. Precision
Agriculture meetings attended/papers (posters) presented:
Meetings Attended
National Irrigation Symposium. Nov. 2000. Session - Precision Irrigation
for Site-Specific Management. Phoenix, AZ.
Papers
Presented
Beltwide Cotton Conferences. Jan. 2000. Perennial weed management with
a position sensitive, multiple-rate spray applicator. San Antonio, TX.
G. Other
developments:
Negative Impacts
The decision to use the larger pivot at Helms instead of the pivot at
Halfway for this project slowed the construction and evaluation of this
system. The construction was further slowed by continuous pivot use
(watering crops) during a summer with little rainfall.
Positive
Impacts
The decision
to use the pivot at Helms instead of the one at Halfway will, over time,
provide up to 130 acres (versus 30 acres) to evaluate site-specific
irrigation and chemigation. The construction of an additional water
well at Helms should further increase the utility of this pivot as a
research tool.
The use
of water well pressure regulating equipment to control pivot pressures
as flow rates change is less complicated and less expensive (initial
cost) than the variable speed motor drives that were initially proposed.
The Opto
22 industrial control equipment offers much greater flexibility for
irrigation control and data gathering (remote sensor input) than the
programmable logic controllers that were initially proposed.
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