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Project No. 1908

L.L. Manske and H. Goetz

Native Range Fertilization with Ammonium Nitrate and Urea

A considerable amount of native range fertilization research has previously been conducted in North Dakota. This fertilization research was conducted by using ammonium nitrate as the source of nitrogen. Most commercial fertilizer suppliers no longer handle ammonium nitrate because of potential storage problems and carry only urea as a source of nitrogen. One purpose of this study was to test if similar rated of ammonium nitrate and urea would give similar results on rangeland. If the results were not similar would there be a relationship between the two sources of nitrogen that could be used to convert previously conducted research data using ammonium nitrate to predict the results using urea on rangelands. Previous range fertilization research has documented an undesirable shift in grass species composition to predominantly cool season species with annual treatments of nitrogen. A second purpose of this study was to test if biennial treatments of nitrogen would reduce the shift of the species composition.


A small plot study that compares fertilization of native range between ammonium nitrate and urea applied annually and biennially was started at the Dickinson Experiment Station in the spring of 1982. The fertilization treatments were 40 and 60 pounds of nitrogen per acre applied annually and biennially, and 100 pounds of nitrogen per acre applied biennially for ammonium nitrate and urea. Each of the three replications contained two control plots of no treatment. The fertilizer was broadcast applied on 4 May 1982-1985 for the annual treatments and in 1982 and 1984 for the biennial treatments.

The data that were collected from these plots were: above ground herbage production, quantitative species composition, soil moisture and soil nutrient content at increments to 48 inches in depth. The above ground herbage production was sampled by clipping to ground level inside 1/4m2 quadrats with the herbage separated into seven categories, cool short, warm short, cool mid, western wheatgrass, warm mid, sedge and forbs. The samples were oven dried at 80oC. The mean herbage production for each category and the total production from each plot were determined for each clipping period. Quantitative species composition data for each plot were collected by the ten pin point-frame method with fifteen hundred points read for each treatment. Soil moisture was collected by the gravimetric method. Soil nutrient samples were collected using the one inch Veihmeyer soil tube. The samples will be analyzed for nutrient content by the soils laboratory at North Dakota State University.

Results and Discussion

Mean total above ground herbage production for the four years of this study are shown in table 1. The herbage production on the unfertilized control plots was generally similar between 3 of the 4 years. The effects of the fertilization was variable between rates and years.

The number of days between fertilization application and the first measurable precipitation was variable between years. The number of days was 3, 2, 33 and 9 for 1982, 1983, 1984 and 1985, respectively. The length of time between application and first precipitation seems to greatly influence the effects of the fertilization treatments. Table 2 shows the mean percentage of herbage production increase for the fertilization treatments compared to the herbage production on the unfertilized control plots. A short period from application to precipitation occurred in 1982 and 1983. A mid and long period occurred in 1984 and 1985. Both the ammonium nitrate and the urea had reduced effects on herbage production increase in 1984-1985.

Ammonium nitrate and urea have not had similar effects on the herbage production at the same rates of treatment. The differences in the effects have not been constant over the years. Volatization of the ammonia in the fertilizer seems to be a problem with broadcast applied fertilizer on grassland. This problems seems to be greatly increased as length of time between application and the first precipitation is increased for both ammonium nitrate and urea. This seems to effect urea to slightly greater extent than ammonium nitrate.

There is a difference in effect on herbage production between ammonium nitrate and urea. This difference is not constant between rates nor years.

Additional research data needs to be collected on this study before definitive conclusions on the differences in the effects of annual vs biennial application on the species composition can be made.

Table 1. Mean Total Above Ground Herbage Production
Treatment lbs of nitrogen/acre 1982 1983 1984 1985 Mean
Control 1124 1148 2386 1112 1443
Ammonium nitrate
40EY 1898 1731 2794 1208 1908
40EOY 1687 1436 2667 1168 1740
60EY 1989 1696 3140 1317 2036
60EOY 1901 1790 2953 1272 1979
100EOY 2360 1664 2945 1238 2052
40EY 1918 1763 2622 1167 1867
40EOY 1606 1370 2549 1044 1642
60EY 1710 1711 2636 1238 1824
60EOY 2073 1584 2584 1044 1821
100EOY 2431 1864 3040 1309 2161
EY = annually

EOY = biennially


Table 2. Mean Percentage of Herbage Production Increase Compared to Unfertilized Control
Treatment lbs of nitrogen/acre 1982-1983 1984-1985 1982-1985
Ammonium nitrate
40EY 60 14 32
40EOY 38 10 21
60EY 62 27 41
60EOY 63 21 37
100EOY 77 20 42
40EY 62 8 29
40EOY 31 3 14
60EY 51 11 26
60EOY 61 5 26
100EOY 89 24 50
EY = annually

EOY = biennially

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