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 fifth year of field work was completed in 1994 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 NW1/4, 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 (Figure 1). Herman Meyer owns the site, while farmer-cooperator Stan Hokana operates the site.

Table 1 summarizes the activity that occurred at the site for project year 1994. Table 2 summarizes the activity that is planned at the site for project year 1995. Table 3 summarizes weather, nitrogen management, irrigation management, and yield information with comparisons to Oakes Test Area (OTA) averages for the project history, i.e., the 1990 through 1994 seasons.

Highlights of BMP Project Results through 1994.

1. Corn grain yields for the four quadrants at the site have averaged 117 bu/ac for the years 1990-1994, which is within 3% of the average irrigated corn yield of 114 bu/ac in the Oakes Test Area (OTA) for the same period. Yields averaged 159 bu/ac in 1994, 20 bu/ac better than the OTA average.

   On-the-go yield monitoring clearly shows the spatial trends in grain yields across the field. The north half of the field continues to exhibit lower corn grain yields than the south half of the field. Yield monitoring appears to be a valuable tool in assessing soil variability and for designing strategies to more precisely manage chemical inputs.

2. Nitrogen management has resulted in average nitrogen savings of 27% compared to OTA averages for 1990-1994. Nitrogen application amounts were 35%, 33%, 40%, 5%, and 20% below OTA averages for 1990, 1991, 1992, 1993, and 1994, respectively. The five-year average N application at the site has been 111 lb N/ac, while the OTA average has been 152 lb N/ac for the same period.

3. Irrigation management has resulted in irrigation water savings of 34% compared to OTA averages for irrigated corn for 1990-1994. Water application amounts were 25%, 25%, 43%, 34%, and 36% below OTA averages for 1990, 1991, 1992, 1993, and 1994, respectively.

4. Soil nitrogen showed a slight increase from 1993. Poor yields in 1993 led to more carry over of nitrogen unused by the crop. Data from nitrogen plots indicate that soil nitrogen can be lowered to as little as 10 lb/ac without affecting yield in adequate fertilization occurs. However, yield models for application of fertilizer materials should be developed that are sensitive to environmental conditions that could under or over utilize fertilizer.

5. Leachate nitrate concentration appears to be stabilizing. In the disturbed profile lysimeters, average nitrateŠnitrogen (NO3ŠN) concentrations reached a peak of 97 ppm NO3-N in June 1991 and have decreased since then. Concentrations in May-June 1994 were about 10-12 ppm NO3-N. In the undisturbed profile lysimeters, average leachate NO3ŠN concentrations rose to a maximum of 157 ppm NO3-N in April 1990 and have generally declined since. Average concentrations throughout the 1994 growing season have increased slightly from 1993 values and range between 10-25 ppm NO3-N.

6. Ground water nitrate concentration averages near the top of the surficial aquifer increased after the start of irrigation, reached a peak of about 40-46 ppm NO3-N in June 1991 through May 1992, and have shown a decreasing trend since then. Average concentrations in October 1994 were less than 20 ppm NO3-N. Ground water concentrations have begun to stabilize with small annual fluctuations in concentration. It has taken four cropping seasons after initiation of irrigation to stabilize NO3-N ground water concentrations. NO3-N concentrations are vertically distributed from contact with organic carbon from the soil surface that aids in heterotrophic denitrification.

7. Tile drain nitrate concentration averages have increased from about 2Š3 ppm NO3ŠN at the start of the study to about 4-6 ppm NO3ŠN at the start of the 1991 season and continue to remain at that level. The use of a chloride tracer has identified depression focused recharge as the source of several anomalous spikes in NO3-N in the drain effluent. The presence of subsurface drainage has influenced the stratification of N in the aquifer. The presence of microbes that can denitrify around and in the tile drains along with denitrification in the surface of the aquifer has dramatically reduced concentrations of NO3-N exiting the field in the drainage water.

Derby, N. E. 1997. Depression focused recharge and solute transport to a shallow aquifer in Southeastern North Dakota. M.S. thesis, North Dakota State University.

Hutson, J.L. and R.J. Wagenet. 1992. LEACHM: Leaching Estimation And Chemistry Model. Continuum vol. 2. Vers. 3. Water Resources Institute., Cornell University., Ithaca, NY.

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.

Schindler, Frank. 1996. Redistribution and fate of applied 15N-enriched urea under irrigated continuous corn production. M.S. thesis, North Dakota State University.

Publications

Costa, J.L., R.E. Knighton and L. Prunty. 1994. Model comparison of unsaturated steady-state solute transport in a field plot. Soil Sci. Soc. Am. J., 58:1277-1287.

Derby, N.E., Knighton, R. E. and D. D. Steele. 1994. Temporal and spatial distribution of nitrate nitrogen under best management practices. p. 37-45. In proceedings of North Dakota Water Quality Symposium, Mar. 29-31, 1994. Fargo, North Dakota.

Derby, N.E. and R.E. Knighton. 1995. Depression focused recharge and solute movement to a shallow unconfined aquifer. p. 348. In Agronomy Abstracts. ASA, Madison, WI.

Derby, N. E. 1997. Depression focused recharge and solute transport to a shallow aquifer in Southeastern North Dakota. M.S. thesis, North Dakota State University.

Knighton, R.E. and W.L. Albus. 1995. Temporal variations in nitrogen loading to ground water as affected by cropping system. p. 347. In Agronomy Abstracts. ASA, Madison, WI.

Parker, B.A. and R.E. Knighton. 1995. Modeling soil water and nitrogen in undisturbed lysimeters under irrigated continuous corn production. p. 199. In Agronomy Abstracts. ASA, Madison, WI. Schindler, F.V. and R. E. Knighton. 1994. Redistribution and fate of applied 15N-enriched urea under irrigated continuous corn production. p. 46-56. In proceedings of North Dakota Water Quality Symposium, Mar. 29-31, 1994. Fargo, North Dakota.

Schindler, Frank. 1996. Redistribution and fate of applied 15N-enriched urea under irrigated continuous corn production. M.S. thesis, North Dakota State University.