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 third 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 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). 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 1992. Table 2 summarizes the activities that are planned at the site for project year 1993. Lysimeters, both disturbed and undisturbed, have been extensively used to determine water and nitrogen balances in the crop root zone. Neutron attenuation has been used to estimate available water in the disturbed profile lysimeters in order to schedule irrigation treatments. Time Domain Reflectometry (TDR) has been used in the undisturbed profile to measure water contents in the profile on a weekly basis during the growing season and this data will eventually be used to simulate movement of chemicals within the lysimeters. Leachate is collected from these lysimeters on a weekly basis to assess the effect of irrigation on movement of fertilizers and pesticides out of the root zone. A limited number of pesticide analyses were done at the end of September on leachate from the lysimeters.

To complement the leachate data, ground water observation wells are monitored throughout the year to determine nitrogen loading to the ground water. Each monitioring site consists of a cluster of three wells screened at different depths. In addition to the clustered wells, four wells have been installed which enable sampling at six inch intervals in the top four feet of the ground water. Tile drains are also monitored throughout the year to determine nitrogen load and the amount of water flowing in the drains. Pesticide residues were analyzed from tile drains, and from the shallow and medium ground water monitoring wells in the fall of 1992.

The effects of different rates and timing of fertilizers on crop yield are being studied in nitrogen plots within the quarter-section. From these trials, fertilizer best management practices will be developed. Intensive soil sampling has also been done within these plots to look at the effects of applied versus mineralized nitrogen on crop response. To determine a nitrogen mass balance for these plots it is necessary to look at the uptake of nitrogen within the plant, so plant samples were taken at silking and harvest for nitrogen analysis.

Best management practices have been employed on the full quarter-section with respect to fertilizer timing and amounts. Soil samples are taken before planting to determine fertilizer rates to achieve a particular yield goal. Crop phenology is monitored closely and yields are taken which are representative of the entire quarter-section in order to determine how well yield goals have been met.

Table 2 summarizes the proposed activity at the project site for 1993. Activiites will be quite similar to 1992 with some minor changes which reflect experience gained from the past year. With the addition of three more transects of ground water monitoring wells, the number of water samples will increase dramatically and will allow tracking of water constituents on a 660 ft grid. These additional measurements will help us expand our database for simulation modeling. In addition to the increased ground water monitoring, soil sampling for 15N will be conducted in 1993 to determine residence times of N in the undisturbed lysimeters and transport time through the root zone to the tile drains. It is also hoped that 15N can be distinguished from 14N in the plant tissue.

Highlights of 1992 Results.

1. Tile drain flows of water were on average smaller in 1992 than in 1991. Tile drain flows of nitrate-nitrogen, nitrite-nitrogen, ammonium-nitrogen, and total nitrogen at all four manholes was smaller in 1992 than in 1991 with the exception of nitrate in tile drain T01 which was within 1lb of the 1991 total. Nitrate-nitrogen concentrations at all manhole locations were below 10 ppm for 1992 but show an increasing trend of 0.75 ppm/yr with some seasonal increases in late spring to early summer above 10 ppm.

2. Total nitrogen losses below the root zone in the disturbed profile lysimeters was considerably smaller in 1992 than in 1991. On average, the total nitrogen loss was 20.3 lb/acre in 1992, 82.3 lb/ac in 1991, and 35 lb/ac in 1990. Average drainage in the disturbed lysimeters was 5.0 inches in 1992, 4.6 inches in 1991, and 2.7 inches in 1990.

3. A 30% savings in fertilizer-N over the test area average has been realized due to nitrogen plot research. Grain yield versus applied nitrogen relationships are better understood and will allow us to modify current best management practices.

4. The four irrigation management treatments used in 1991 were again used--on different quadrants--in 1992. Less irrigation was applied in 1992 than in 1991, since the site received more rainfall and the season was cooler. The corn grain yield was smaller in 1992 than in 1991 because an early-season frost damaged the crop.

5. A 25% savings in irrigation over the test area average has resulted in the last three years of research at the BMP site. Signicant progress has been made toward refining irrigation sheduling for continuous corn production at the BMP site.

6. Atrazine was detected again in similar concentrations (highest concentration was approximately 5 ppb) and locations as in 1990. Degradation products of atrazine were also sampled in ground water and found to be significantly higher (approx. 30 ppb) than the parent compound. This would suggest that signicantly higher concentrations of atrazine existed in the ground water before our sampling.

7. Potassium concentrations in gravity drainage from the undisturbed lysimeters was found at almost 100 times the concentration of the vacuum extractor drainage. This would suggest that potassium could possible be used as a tracer for to quantify preferential flow at this particular site.

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. 1992. Monitoring leachate losses with large undisturbed profile lysimeters. In Proceedings of North Dakota Water Quality Symposium, Mar. 25-26, 1992. Bismarck, North Dakota.

Knighton, R.E. and W.L. Albus. 1992. Management Systems Evaluation Areas: A study of water quality in the midwest. In Proceedings of North Dakota Water Quality Symposium, Mar. 25-26, 1992. Bismarck, North Dakota.

Olson, J.M. and R.E. Knighton. 1992. Monitoring and stratification of nitrogen in a surficial unconfined aquifer. In Proceedings of North Dakota Water Quality Symposium, Mar. 25-26, 1992. Bismarck, North Dakota.

Steele, D. D., Stegman, E. C., Prunty, L. D., and Knighton, R. E. 1992. Overview of a field study of best management practices for improved irrigation and fertilizer nitrogen use efficiencies. pp. 28-37. In Proc. of the North Dakota Water Quality Symposium, Bismarck, ND. March 25-26, 1992. North Dakota State University Extension Service, Fargo.