Best Management Practices for Improved Irrigation and Fertilizer Nitrogen Use Efficiencies.

COOPERATING AGENCIES AND PRINCIPAL LEADERS:

NDSU, Agricultural Engineering Department: E.C. Stegman and D.D. Steele
NDSU, Soil Science Department: L.D. Prunty and R.E. Knighton
U.S. Department of Interior, USBR

OBJECTIVES

1. To determine the impacts of BMP's (for irrigation and fertilizer management) on crop responses and on leachate losses (quality/quantity) at major points (root zone, ground water and subdrains) of an irrigated hydrologic system.

2. Develop data sets to adapt and/or calibrate/validate suitable models for integrated management of irrigation and fertilizer nitrogen applications.

3. Develop/evaluate methods for measuring leachate losses from crop root zones.

The second year of field work was completed for the field-scale study of Best Management Practices (BMPs) for deficit irrigation and associated nitrogen fertilizer management on soils representative of the Garrison Diversion Unit. The "test site" selected within the 5000 acre Test Area of the Garrison project encompasses 160 acres of NW 1/4, Sec. 29, T. 130 N., R. 59 W., in Dickey County of North Dakota. Approximately 132 of the 160 acres are irrigated by a center pivot irrigator (Fig. 1). The site is owned by Herman Meyer and operated by farmer-cooperator Stan Hokana. Table 1 summarizes the activities that occurred at the site for project year 1991, and Table 2 summarizes the proposed activities at the site for 1992.

Highlights of 1991 Results.

1. Irrigation treatments for the four quadrants on the quarter section resulted in larger differences in irrigation amounts between quadrants for the 1991 season than were observed in the 1990 season. Irrigation amounts in 1991 were 4.10, 4.60, 5.29, and 7.85 inches for the NW, NE, SE, and SW quadrants, respectively. For comparison, irrigation amounts in 1990 were 7.03, 7.75, 7.65, and 7.56 inches for the NW, NE, SE, and SW quadrants, respectively.

2. The disturbed lysimeters are continuing to provide valuable information on water and nitrogen leaching below the root zone of the corn crop. Typical drainage rates are 0.05 inches per day for portions of the growing season, with annual totals ranging from 2 to 6 inches. Peak drainage has tended to occur during the months of May and June for both 1990 and 1991. Typical nitrogen losses below the root zone have been approximately 1 pound per acre per day for portions of the growing season, with growing season totals ranging from 10 to 76 pounds per acre. Peak fluxes of nitrogen have also tended to occur during the months of May and June for both 1990 and 1991.

3. Drainage from the undisturbed lysimeters in the irrigated areas averaged 13.7 and 5.7 inches in 1990 and 1991, respectively. Drainage in the nonirrigated areas averaged 4.6 and 1.7 inches in 1990 and 1991, respectively. The higher drainage amounts in the 1990 season were attributed to higher suction applied to the undisturbed lysimeters in 1990 than 1991; in 1990, a suction of 30 centibars was used, while in 1991, 10 centibars was used. The nitrogen fluxes in the undisturbed lysimeters averaged 85, 168, and 63 lb/acre for all 20 lysimeters for 1989, 1990, and 1991, respectively. The higher nitrogen loss in 1990 than in 1991 corresponds to the higher drainage amounts in 1990 than in 1991. The nitrate concentrations were quite variable with respect to both time and location, with a maximum concentration of nearly 500 ppm.

4. Ground water wells at the site have shown that nitrate concentrations continue to be stratified within the surficial aquifer, with higher concentrations near the water table (shallow wells) than near the constricting layer (deep wells). This was also the case prior to irrigation of the quarter in 1989. All of the shallow and medium wells reached N-NO3 concentrations above 10 ppm at some point during 1990 or 1991, but not all have remained above that level. The maximum concentrations of NO3-N for 1991 were near 120 ppm in the shallow wells, 140 ppm for the medium wells (2 feet below the water table) and 3.5 ppm for the deep wells. The 120 ppm and 140 ppm maximums noted here were in the same cluster (C9) of wells. During construction of the wells and lysimeters, the transects were fertilized but not cropped, which may have led to higher N concentrations now leaching to the ground water.

5. A multi-level osmotic ground water sampler was tested in the field and laboratory. The calibration of the sampler showed that it is capable of giving an accurate indication of the natural ambient water chemical gradient. The osmotic multi-level sampling method is effective in detecting the presence of contaminants even in low concentrations.

6. Nitrate-nitrogen concentrations at all four of the tile drain manhole sampling locations at the site have been below 10 ppm for 59 out of 60 sampling dates for 1990 and 1991, with a maximum concentration of 14.7 ppm on 5/8/91.

7. Statistical analysis of the 1991 corn grain yield response to different levels of applied N for each quadrant indicates that no significant yield response to additional N is obtained above 120 lb N/ac for the NW, SE, and SW quadrants, 80 lb N/ac for the NE quadrant, and 20 lb N/ac for the dryland area. A quadratic regression of average grain yield versus applied nitrogen for all irrigated nitrogen plots indicates a positive response in grain yield to applied nitrogen for nitrogen levels up to 160 lb/ac, with little response to nitrogen levels above 160 lb/ac. A similar regression for corn grain yield versus total soil nitrogen (spring soil test + applied N) indicated a positive correlation to total N for total N levels up to approximately 225 lb/ac.

Esser, Dale. 1992. Personal communication with Dale Esser, United States Bureau of Reclamation, Oakes, ND.

North Central Computer Institute. 1985. Program Design Documentation for the Water Management Simulation Model in the North Central States. NCCI Conference: Water Management Simulation Using DRAINMOD, August 13-15, 1985, Madison, WI. pp. 15-17.

Ritchie, S. W., Hanway, J. J., and Benson, G. O. 1986. How a corn plant develops. Special Report No. 48 (Revised January 1986). Iowa State University of Science and Technology, Cooperative Extension Service. Ames, Iowa.

Publications

Derby, N. E, and R.E. Knighton, 1991. Monitoring leachate losses with large undisturbed profile lysimeters. p. 216. In: Agronomy Abstracts. ASA, Madison, WI.

Gregor, B. L., and Stegman, E. C. 1991. Intelligent controller applications to center pivot management. Presented at the ASAE symposium "Automated Agriculture for the Twenty-First Century," Chicago, IL. December 16-17.

Hoffmann, L. L., Knighton, R.E. and J.R. Fleeker. 1991. Pesticide mobility in irrigated northern great plains soils. p. 44. In: Agronomy Abstracts. ASA, Madison, WI.

Olson, J. M. 1991. Monitoring and stratification of nitrogen in a surficial unconfined aquifer. M.S. Thesis, NDSU, Fargo, ND.

Olson, J. M. and R. E. Knighton. 1991. Temporal and spatial distribution of nitrogen in a shallow aquifer. p. 227. In: Agronomy Abstracts. ASA, Madison, WI.

Olson, J. M., R.E. Knighton, and J.C. Patch. 1991. Stratified solute monitoring with a multi-level sampler. 36th Annual Midwest Groundwater Conference, Indianapolis, IN, 9-11 October 1991.