Work was begun in 1989 to prepare a "test" center pivot site for field-scale study of Best Management Practices for deficit irrigation and associated nitrogen fertilizer management on soils representative of the Garrison Diversion Unit. The "test" site was selected from lands within a 5000 acre Test Area of the Farrison project, located South of Oakes, ND. The test site encompasses about 130 acres of NW 1/4, Sec. 29, T. 130 N., .59 W., in Dickey County of North Dakota. The farmer-cooperator is Stan Hokana.
A principal objective of the project is to determine the impacts of BMP's on leachate losses (quantity and quality) from the root zone, to the ground water and to the subdrain system in this field. To begin the project an initial detailed data set was required to characterize physical and chemical properties of the soils in the field, and to characterize the existing ground water quality beneath the field. Procurement, construction, and installation of sampling equipment and associated instrumentation began in 1989. The following discussion summarizes activities in the key aspects of this project.
Survey crews (USBR), in early spring, established bench marks at 330 feet intervals [Fig. 1], and then staked the field at this grid spacing. Probe trucks were then utilized to obtain soil cores at each intersection (approx. 64 sites) of the grid. Two borings were taken at each site. One boring was sampled by horizon intervals and the second boring was sampled at 0-6", 6-12", 12-24", 24-36", etc to about 10 feet or to the water table. Drill hole logs were prepared per USBR-Interior Land Classification methods and also per USDA-Soil Classification Methods (NDSU- Soils). The soil core materials are being analyzed (NDSU-Soils, USBR-Bismarck) for particle sizes, nitrogen (organic and inorganic), phosphorus, potassium, major cations/anions, PH, EC, and organic carbon. The initial soils data set development (i.e. labwork) is estimated to be about 50 percent completed.[Fig.1] NW 1/4 Sec 29 - Schematic layout of Test field illustrating 330 foot grid lines, field sector or quadrant boundaries and tile line locations.
Nested ground water observations wells (3 per site) were installed on two transect lines [Fig. 2] across the "test" field. The observation wells were completed by USBR crews in the early winter of '88-'89. Nine well sites are located on each transect. Each site of 3 wells [Fig. 3] allows sampling of the ground water in the first foot below the water table, the second two foot interval, and at the bottom confining layer of the saturated thickness. All wells were constructed from PVC materials (casings and screens) with 2 foot screen lengths. Beginning Jan. of 1989, all wells have been measured (USBR) monthly for water table depth and for water samples. Water samples are preserved by freezing for temporary storage. The water samples are being analyzed for nitrate-N, nitrite-N, ammonium, ortho-P, major cations/anions (every other month), pH, and EC.[Fig. 2] NW 1/4 Sec 29 - Schematic illustrating location of transect lines, and approximate locations of groundwater observation wells and disturbed soil profile lysimeters.
[Fig. 3] NW Sec 29 - Schematic illustrating relative position of nested groundwater observation wells. Typical screen depths: shallow well screen 8 - 11', medium well screen 10 - 12', deep well screen 18 - 20', till barrier 21'.
Water samples were collected (USBR and/or NDSU-Soils) monthly (Jan.-Sept.) and twice per month (Oct.-Dec.) from each of four manhole entry points that are available in the "test" field [Fig. 1]. Water samples are preserved by freezing for temporary storage. Analyses in 1989 have included nitrate-N, and major cations/anions (every other month).
Lysimeters will be utilized in this "test" field as primary instruments for sensing the root zone water balance and for measurement of leachate losses from the crop root zone. The "test" filed, for evaluation of irrigation management regime impacts, will be divided into 4 sectors or approximate quadrants as dictated by the subdrain placements. A "disturbed soil profile" lysimeter (4' x 5' cross section) was installed in each quadrant of the test field in July-August. All four lysimeters were filled with a Hecla soil series that was obtained from a common borrow site in the SE quadrant of the test field. The common soil in these lysimeters is intended to provide a common medium for determining the degree to which "different" water management regimes are achieved in each field quadrant.
Detailed profile sampling was done at the borrow site to document soil physical and chemical properties by 6 inch profile intervals and by horizons. The profile for each lysimeter was carefully excavated by 6-8 inch layers to the cross section dimensions of the lysimeter (by utilizing a template box). Each excavation or lift was placed in a plastic protected plywood box (minimizing water evaporation) for transport to the lysimeter site. Each layer was then placed (in natural profile order) and recompacted to near natural bulk density in the lysimeter [Table 2].
The cross section layout and placement depths of the disturbed profile lysimeters is illustrated in [Fig. 4]. As indicated, the drainage from these lysimeters will be monitored in manholes which are hydraulically connected to each lysimeter.
[Fig. 4] NW Sec 29 - Cross-section of a disturbed soil profile lysimeter installation.
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