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.

1. Corn grain yields for the four quadrants at the site averaged 121 bu/ac for the years 1990 to 1995. Yields were 3% above the average irrigated corn yield of 117 bu/ac for other commercial growers of irrigated corn in the Oakes Test Area (OTA) for the same period. Yields were significantly lower in the north half of the field (108 bu/ac average) than the south half of the field (127 bu/ac average).

2. Nitrogen management has resulted in average nitrogen (N) savings of approximately 22% compared to other commercial growers of irrigated corn in the OTA for 1990 to 1995. The six-year average N application at the site has been 119 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 approximately 31% compared to other commercial growers of irrigated corn in the OTA for 1990 to 1995. The irrigation totals for the site averaged 5.27 inches per season, compared to application totals averaging 7.6 inches for other commercial growers of corn in the OTA for the same period.

   Four irrigation scheduling methods were implemented at the site and rotated between quadrants of the field over the study period. The irrigation scheduling methods and average seasonal application totals were: A) scheduling based on tensiometer and infrared canopy temperature measurements, 5.57 inches; B) scheduling based on a water balance method with variations in the allowed depletions of plant-available water, 5.11 inches; C) using a modification of Method B that applied 20% smaller irrigation amounts at each irrigation, 3.97 inches; and D) using estimates of crop water use from the growth model CERES-Maize, 4.62 inches.

   The irrigation scheduling methods did not differ statistically from one another in seasonal irrigation totals nor in their effects on crop yield. Seasonal irrigation totals were significantly affected by the variability in weather from year to year, but not by the quadrant of the field. Residual effects of irrigation scheduling were not present, i.e., irrigation scheduling in a given season did not affect the amount of irrigation water required in the next season nor the yield the next season. Therefore, moisture ÒbankingÓ from one season to the next is not recommended for the climate and soil types at the site. A detailed analysis and discussion of the irrigation scheduling experiment is presented in the Irrigation Management Section.

4. Nitrate-nitrogen concentrations in the ground water rose after the initiation of irrigation in the 1990 season and have declined dramatically since. The increase in nitrate-nitrogen (NO3ÐN) concentrations in the ground water is attributed to increased mineralization of organic N in the soil profile at the onset of irrigation. The decline in NO3ÐN concentrations is attributed to careful irrigation water management, careful nitrogen fertilizer management, and biological denitrification or immobilization in the subsurface drains.

   In the undisturbed-profile lysimeters within the irrigated area, NO3-N concentration averages reached a peak of 157 mg L-1 on 25 April 1990 and decreased to an average of 7 to 8 mg L-1 in mid-October to mid-November 1995.

   In the disturbed-profile lysimeters in the southeast, northeast, and northwest quadrants of the irrigated area, NO3-N concentration averages reached a peak of 87 mg L-1 on 12 June 1991 and decreased to an average of 3 to 4 mg L-1 in mid- October to mid-November 1995.

   In the shallow- and medium-depth ground water wells along two transects (ÒCÓ and ÒGÓ) at the site, NO3-N concentration averages reached a peak of 43 mg L-1 on 18 February 1993 and decreased to an average of 21 to 22 mg L-1 in mid- October to mid-November 1995.

   In the subsurface drain sampling locations for water leaving the site through the drains, NO3-N concentration averages reached a peak of 7 mg L-1 on 2 July 1991 and decreased to an average of 4 to 5 mg L-1 in mid-October to mid- November 1995. Four short-lived increases in NO3-N were detected at these sampling locations and were attributed to bypass flow in the soil profile. For example, the average NO3-N concentration in 1991 was 4 mg L-1 on 1 May, rose to 12 mg L-1 on 8 May, and fell back to 4 mg L-1 on 15 May.

Albus, W., J. Weigel, and H. Sayfikar. 1990. The effect of planting date on irrigated corn in southeastern North Dakota. ND Farm Res. 48(2 Sept./Oct.):22Ð25.

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.

U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Climatic Data Center. 1982. Monthly Norms of Temperature, Precipitation, and Heating and Cooling Degree Days, 1951Ð1980; North Dakota. In Climatography of the U.S., No. 81.

Publications

Steele, D.D., E.C. Stegman, and R.E. Knighton. 1996. Irrigation management for corn in the northern Great Plains. J. Prod. Ag. (In review at journal).

Steele D.D., T.F. Scherer, L.D. Prunty, and E.C. Stegman. 1996. Correction frequencies for four irrigation scheduling methods for corn. Appl. Engr. Agric. (In review as ASAE manuscript number SW-3045.)

Steele, D.D., R.E. Knighton, and E. C. Stegman. 1996. Field-scale water quality under continuous, irrigated corn production in the northern Great Plains. Presented at the 1996 International Meeting of the American Society of Agricultural Engineers at Phoenix, AZ, July 14-18, 1996. Paper No. 96-2020. St. Joseph, MI: ASAE.

Steele D.D., T.F. Scherer, L.D. Prunty, and E.C. Stegman. 1996. Correction frequencies for four irrigation scheduling methods for corn. In Proc. International Evapotranspiration and Irrigation Scheduling Conference. San Antonio, TX, 3-6 Nov. (In press, paper no. 8-15.)

Ray, S.K. 1996. Center pivot system analysis for integrated irrigation and nitrogen management for spatially-varied soils. Ph.D. Dissertation. (In revision after successful defense.)

Steele, D.D., and R.E. Knighton. 1995. Nitrogen and irrigation recommendations for corn in southeastern North Dakota. Crop Production Guide 1996. No. 6, pp. 225-227. North Dakota State University Extension Service, Fargo.

Steele, D.D., and R.E. Knighton. 1995. Research on irrigated corn near Oakes, ND. In: Water Spouts, No. 150 (September). North Dakota State University Extension Service, Fargo.