COOPERATING AGENCIES AND PRINCIPAL LEADERS:

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

Project work began in 1989 to study the effects of Best Management Practices (BMP's) on leachate losses (quantity and quality) from the root zone, to the groundwater and to the subdrain system on a "test" site located on the NW1/4 of section 29 of T. 130 N. and 59 W. in Dickey Co., North Dakota. Project objectives are to:

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.

To complement the leachate data, groundwater observation wells are monitored throughout the year to determine nitrogen loading to the ground water. Each monitoring site consists of a cluster of three wells screened at different depths. In addition to the clustered wells, four wells have been installed this year which will enable sampling at six inch intervals in the top four feet of the groundwater. Tile drains are also monitored throughout the year to determine nitrogen load and the amount of water flowing in the drains. A limited number of well and drain samples were analyzed for pesticides in 1990.

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 1b. (see pdf file) summarizes the proposed activity at the project site for 1991. Activities will be quite similar to 1990 with some minor changes which reflect experience gained from the past year. Sampling of the lysimeters will be intensified with respect to cations, pH and EC. Phenology will also be recorded on the lysimeters this year. These additional measurements will help us expand our database for simulation modeling. Phenology will also be taken on the nitrogen plots for the same reasons. Well and tile drain monitoring will follow the same sampling schedule but cations, pH and EC will be monitored more frequently. The following are highlights of project results:

1. Field instrumentation has been successfully installed and instruments are functioning properly. Both the disturbed and undisturbed lysimeters are proving to be valuable tools in monitoring leachate losses in the root zone. Drainage was significantly higher in the undisturbed lysimeters (2.5 in) vs. the undisturbed lysimeters (13.7 in). This large difference is due to suction used in the undisturbed lysimeters. The drainage in the disturbed lysimeters is similar to that in the dryland undisturbed lysimeters (4.6 in) which indicates that irrigation scheduling has been effective in minimizing drainage in the irrigated quadrants.

2. Approximately 14 lb N/ac were lost as leachate which is a good indicator that irrigation management has been a success. However a large amount of nitrogen (100 lb/ac) was unaccounted for and thought to be due to mineralization. This suggests that N recommendations can be further refined to account for this important pool of organic N.

3. A moderate crop response was shown for N fertilizer. Crop productivity appears to be much higher on the south vs. the north half of the field. Productivity differences will help us better manage fertilizer inputs and reduce the potential for groundwater contamination. Soil differences appear to be chemical in nature and due to accumulation of salt; as the northwest quadrant was a groundwater discharge point before drainage.

4. Groundwater observation wells have shown that N is extremely variable and quite stratified. Nitrate appears to stay at the top of the water table and there is limited mixing in the top 4 ft. Nitrate concentrations at the top of the water table exceeded the drinking water standard by as much as 7.6 times. Seventy-eight percent of the shallow wells (top ft) exceeded the standard and sixty-seven percent of the medium (2 ft below the water table) exceeded the drinking water standard. None of the deep wells (at bottom of confining layer) tested above the 10 ppm nitrate standard.

5. Atrazine was detected in a few shallow wells, lysimeter leachate, and one tile drain. Concentrations were below health standards and in subsequent sampling appeared to be decreasing. Soil samples indicate that the bulk of applied pesticides are remaining in the top foot of the soil profile.

The following is a discussion of methodolgies used and developed, along with results obtained by project objective.

1990 Annual Report in PDF format (760K).

Hanway,J.J. 1963. How a corn plant develops. Iowa Cooperative Service Special Report, 48:3-18.