Illinois Fertilizer
Conference Proceedings
January 25-27, 1993
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Michael J. Mainz and Glenn A. Raines1
The objectives of this project were to determine the amount of nitrate and ammonium remaining in the soil at the 0-1', 1-2', 2-3', 3-4', 4-5' sampling depths following 8 and 11 years of a nitrogen rate study using 2 crop rotation programs at Monmouth and Perry, respectively. Total soil nitrogen levels were the lowest at all depths for the zero nitrogen rate treatments in both rotations and locations. The soil N levels in the zero treatments decreased with depth. Highest nitrogen levels occurred at the highest nitrogen application rates. Crop rotations were only significantly different for the deepest sampling for nitrate at both locations and total N and ammonium N at Perry.
Nitrogen rate studies were started in 1980 and 1982 at Perry and Monmouth, respectively. Both locations have 5 nitrogen rates and two crop rotations. At Perry the rates were 0, 80, 160, 240 and 3201bs N/acre for corn and 0, 30, 60, 90 and 120 for wheat until 1990 when the corn rates were changed to 0, 60, 120, 180 and 240 lbs N/acre. There are blocks of continuous corn, rotation corn, soybeans and wheat grown each year at Perry. Monmouth has nitrogen rates on continuous corn and corn following soybeans. Nitrogen rates have been 0, 60, 120, 180 and 240 pounds per acre. Soils at the 2 locations differ in that those at Perry were formed under forest vegetation while those at Monmouth came from a prairie environment. Nitrogen treatments have not been rotated between plots. Nitrogen has not been applied to the soybeans at either location.
Soil samples were taken in 1 foot increments to a depth of 5 feet prior to
nitrogen applications and planting in 1991. A tractor mounted Giddings hydraulic
probe was used to collect the 3 cores per plot. Only those plots planted to
wheat in the spring of 1991 were not sampled. All soil samples were dried and
then stored until funding was obtained for analysis. The entire sample from
each plot was ground in the spring of 1992, divided and then analyzed by Brookside
Farms Laboratory, Inc. using the "Cadmium reduction" method. Total
inorganic N and NO3-N were analyzed for and then NH4-N was determined by difference.
Nitrate nitrogen levels increased with depth and nitrogen (N) application except at the zero and 60 lb N/acre treatments (Table 3). Below the 3 foot depth nitrate levels accumulated to over 12 ppm and greater. Total inorganic N levels are much higher than expected, especially for rotation corn. Inorganic N concentrations from 10-18 ppm were common even following soybeans. Inorganic N concentrations were consistent at all depths and all nitrogen treatments following soybeans (Table 4). It would appear that one year of soybeans is enough to increase soil nitrate levels in the corn treatments not receiving N and decrease those receiving high rates of N. Soil N levels after soybeans were almost equally distributed between nitrate and ammonium N.
Nitrate nitrogen levels in the surface 3 feet were at or below 10 ppm for all N rates and both rotation programs. Only below the 3 foot depth do the nitrate concentrations change greatly for the rotations and N treatments. It would appear that the corn grown on this study in 1990 did an efficient job of utilizing the N in the top 2 feet of the profile. Corn yields virtually leveled off at the 120 and 60 lb/a N rates for continuous and rotation corn, respectively. This might indicate that additional N was not needed by the plants. Nitrogen accumulations in the soil might also indicate additional N that was not utilized. A conclusion can not be arrived at since this is only one years results.
Soil N concentrations at Perry are much lower than at Monmouth. Most of this difference may be due to differences in organic matter content between the 2 sites, 4.2 % + at Monmouth and 1.6 % at Perry. Nitrate nitrogen makes up approximately a third of the total N found in the soil. Differences between crop rotations, N rates and depths was not very great, with the exception of the 240 lb/a N rate at the 4 & 5 foot depths under continuous corn (Table 6). Having some N applied 2 out of 3 years may have helped to even out the N concentrations. Although the total amount of N following wheat was similar to those values following soybeans at Monmouth (Table 4 & 5). It is unfortunate that all the plots planted to wheat were not sampled to help make soybean to soybean comparisons. But, the N for wheat was already applied and we felt it would complicate the issue.
Corn yields continued to increase as N rates increased to 1201b N /acre for
continuous and 240 lb N/acre for rotation corn at Perry (Table
2). Zero N treatment yields are much lower at Perry than Monmouth. Long
term yields for the zero N rates are 35 and 48 bu/a for continuous and rotation
corn, respectively. Much of this difference is due to the inherent productivity
differences between the soil types at the two locations. Total productivity
between the two locations is minimal when nutrients are provided at optimum
levels and normal weather, rainfall and temperature, are achieved.
These results are for only one year, and that year was following 2 very dry years. Even though above normal precipitation levels occurred in 1990 at both locations. The 44 inches of precipitation at Monmouth and 48 inches at Perry may have been enough to move the N deep into or through the soil profile. There is a short tile line draining the N rate study at Monmouth, but, the exact location and length of it is not known. Tile drainage is not needed in the N rate study at Perry and surface drainage is satisfactory.
Both N rate studies have continued since 1991 and we plan to continue them
as long a possible. Plans are underway to do additional deep soil sampling and
N testing in these existing plots as well as on a few farmers fields, if funding
is acquired. Crop yield response to nitrogen rates has been very consistent
at both locations after the unusual weather years are removed. Yield increases
for the crop rotation is much less at Perry than Monmouth. The uniformity of
soil nitrogen levels may partially explain the difference at Perry. The high
organic matter soils at Monmouth appear to be adding considerably to both crop
yields and soil nitrogen levels.
Table 1: Corn yield response to nitrogen rates in 1990. (Monmouth)
Table 2: Corn yield response to nitrogen rates in 1990. (Perry)
Table 3: Soil nitrogen levels at Monmouth, April 1991
Table 4: Soil nitrogen levels at Monmouth, April 1991. Soybeans Previously
Table 5: Soil nitrogen levels at Perry, April 1991. Wheat Previously
Table 6: Soil nitrogen levels at Perry, April 1991
Mainz, M.J., J.Sutor, T. Tinkham and R. Caulkins. 1983-91. Nitrogen Rate Study. Northwestern Illinois Agricultural Research and Demonstration Center, Report of Research Results.
Raines, G.A., T.E. Hallock and M. Vose. 1981-91. Nitrogen Rate Study. Off Agricultural Research and Demonstration Center, Report of Research Results.
